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A high-precision tunable single-frequency fiber laser (T-SFFL) at 1.5 μm based on self-injection locking is experimentally demonstrated. By virtue of an effective filtering and self-injection locking scheme, a stable single-longitudinal-mode operation of the fiber laser is obtained. The fine wavelength tunability is implemented by stretching a uniform fiber Bragg grating in the self-injection loop, and the laser wavelength is tuned from 1550.28 to 1560.40 nm with a tuning accuracy of less than 54 pm. In the whole tuning range of 10.12 nm, an output power of approximately 5 mW and an optical signal-to-noise ratio of 71 dB are synchronously obtained with this laser system. Additionally, the measured laser linewidth is less than 630 Hz and the relative intensity noise is lower than -149 dB/Hz at frequencies from 0.4 to 7.5 MHz. It is believed that this 1.5 μm high-precision T-SFFL can be a promising candidate for the optical communications system applications.

A graphene/epoxy composite based broadband all-optical tunable fiber microcavity filter is presented. The graphene/epoxy composite based microcavity shows the excellent all-optical controlability. Since the light acts on the graphene/epoxy composite directly, the microcavity has stronger optical Kerr effect and photothermal effect induced by the optical pump. Experimental results show that its wavelength tuning range and tuning step reach 25.54 nm and 832 pm/mW, respectively. It is expected to be applied in the fields of tunable optical filters, optical communication, optical sensors, fiber lasers, and spectrum scanning.

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.

Phase-locked laser arrays have been extensively investigated in terms of their stability and nonlinear dynamics. Specifically, enhancing the phase-locking stability allows laser arrays to generate high-power and steerable coherent optical beams for a plethora of applications, including remote sensing and optical communications. Compared to other coupling architectures, laterally coupled lasers are especially desirable since they allow for denser integration and simpler fabrication process. Here, we present the theoretical effects of varying the spontaneous emission factor $\beta $ , an important parameter for micro- and nanoscale lasers, on the stability conditions of phase-locking for two laterally coupled semiconductor lasers. Through bifurcation analyses, we observe that increasing $\beta $ contributes to the expanding of the in-phase stability region under all scenarios considered, including complex coupling coefficients, varying pump rates, and frequency detuning. Moreover, the effect is more pronounced for $\beta $ approaching 1, thus underlining the significant advantages of implementing nanolasers with intrinsically high $\beta $ in phase-locked laser arrays for high-power generation. We also show that the steady-state phase differences can be widely tuned – up to $\pi $ radians – by asymmetrically pumping high- $\beta $ coupled lasers. This demonstrates the potential of high- $\beta $ nanolasers in building next-generation optical phased arrays requiring wide scanning angles with ultra-high resolution.

Free-space optical communications (FSOCs) are gaining popularity as a promising solution to capacity crunch of aerial and satellite backhaul networks for next-generation mobile communication systems. A major technical challenge associated with such FSOC systems in motion is the pointing, acquisition, and tracking (PAT). To facilitate PAT, it is absolutely necessary to steer the optical beam over a wide angle and also adjust the beam divergence angle adaptively to the link condition and the amount of pointing error. The conventional methods to steer the optical beam and/or to adjust the beam divergence angle rely on mechanical mechanisms. Recently, the optical beam steering technique using variable focus lenses has been proposed and demonstrated. By using an on-axis variable focus lens followed by two decentered variable focus lenses, we can steer the optical beam over a wide range in a non-mechanical fashion. In this paper, we explore the possibility of using variable focus lenses for the realization of beam steering and adaptive beam control for FSOCs. For this purpose, we employ three variable focus lenses, one on-axis lens for adaptive beam divergence control and two decentered lenses for two-dimensional beam steering. We demonstrate the simultaneous beam steering and adaptive beam control capability of this variable focus lens-based system over a 104-m long free-space optical link. We evaluate the maximum beam steering angle and beam quality as we vary the offset distance of decentered variable focus lenses. Also evaluated experimentally is the impact of gravity on the beam quality. Finally, we show that the beam steering and adaptive beam control techniques implemented by variable focus lenses improve the performance of 10-Gb/s FSOC system considerably in the presence of pointing errors.

Ensuring high speed physical layer confidential data exchange in classical optical fiber channels is a critical challenge. In this letter, we experimentally demonstrated a physical secure optical communication system based on temporal spreading-then-random phase encryption scheme for secure transmission of 25 Gb/s intensity-modulated signal. Commercial low cost continuous-wave laser is employed as the optical source, and a chirped fiber Bragg grating followed by a phase modulator is utilized as a two-dimensional encryption module. Successful encryption and decryption of 25 Gb/s confidential data have been achieved by optimizing optical hardware parameters. The demonstrated system can combine the advantages of hardware and digital encryption, exhibiting great potential for providing physical layer security in future high-speed secure optical communication systems.

This paper presents and investigates a dual-hop mixed radio frequency (RF) and underwater optical communication (UWOC) system. In the proposed system, an unmanned aerial vehicle (UAV) such as drone (S) located at low altitude is transmitting data signal towards the destination (D) which is located under water such as a submarine through a decode and forward (DF) relay (R) mounted on a ship over the sea surface. The data signal is transmitted from the UAV towards the relay located on the ship via RF channel modelled by the Nakagamim distributed fading statistics. The relay decodes the received RF data signal and re-transmits it towards the destination via visible light channel modelled by Exponential Generalized Gamma (EGG) distribution. Using the DF relaying protocol, we derive closed form analytical expressions for the outage probability and average bit error rate of the proposed mixed RF-UWOC system. Additionally, UAV optimal altitude analysis has been carried out to find the optimal elevation angle corresponding to the optimal altitude of the UAV where the system performance is maximized. The numerical simulation is carried out to support the performance analysis of the mixed RF-UWOC system and shows the influence of the various channel parameters such as air bubbles, UAV altitude, water salinity variations and scintillation on the end to end performance of the mixed RF-UWOC system.

This present work is about simulating and analysing a Vertical Cavity Surface Emitting Laser (VCSEL) structure used in optical fibre communication systems. In this paper a VCSEL structure made of seven Quantum Wells of Indium Gallium Arsenide Phosphide (InGaAsP) emitting at 1550 nm is simulated. The device is analysed looking at the following characteristics: Direct current current and voltage (IV) characteristics, light power against electrical bias, optical gain against electrical bias, light distribution over the structure, output power and threshold current. Specification of material characteristics, ordinary physical models settings, initial VCSEL biasing, mesh declarations, declaration of laser physical models, their optical and electrical parameters were defined using Atlas syntax. Mirror ratings and quantum wells are the two main parameters that were studied and analysed to come up with structure trends. By determining important device parameters such as proper selection of the emission wavelength and choice of material; a VCSEL with an output power of 9.5 mW was simulated and compared with other structures.

Dynamic control of motion at the molecular level is a core issue in promoting the bottom-up programmable modulation of sophisticated self-organized superstructures. Self-assembled artificial nanoarchitectures through subtle noncovalent interactions are indispensable for diverse applications. Here, the active solar renewable energy is used to harness cholesteric liquid crystal (CLC) superstructure devices via delicate control of the dynamic equilibrium between the concentrations of molecular motor molecules with opposite handedness. Thus, the spectral position and handedness of a photonic superstructure can be tuned continuously, bidirectionally, and reversibly within the entire working spectrum (from near-ultraviolet to the thermal infrared region, over 2 μm). With these unique horizons, three advanced photoresponsive chiroptical devices, namely, a mirrorless laser, an optical vortex generator, and an encrypted contactless photorewritable board, are successfully demonstrated. The sunlight-fueled chirality inversion prompts facile switching of functionalities, such as free-space optical communication, stereoscopic display technology, and spin-to-orbital angular momentum conversion. Motor-based chiroptic devices with dynamic and versatility controllability, fast response, ecofriendly characteristics, stability, and high efficiency have potential to replace the traditional elements with static functions. The inexhaustible natural power provides a promising means for outdoor-use optics and nanophotonics.

Distributed vibration sensing (DVS) utilizes an optical fiber as an array of virtual strain sensors. It can reveal dynamic strain distributions such as seismic events and car traffic, thus giving a new function to existing optical communication fibers. In this work, we use optical frequency domain reflectometry (OFDR) to investigate the dynamic strain distribution along an optical fiber implemented in a deployed aerial optical fiber cable that vibrates with the wind. The OFDR setup is customized for distant location interrogation with a high repetition rate of the probe light and overcomes the OFDR drawbacks of short measurement range and low repetition rate, thus enabling application to the investigation of dynamic strain along a range of telecommunications outside a plant. Sub-1-m spatial resolution measurements revealed that dynamic strain along the optical fiber in an aerial cable depends on the deployment condition. It also provides the deployed optical telecommunication fiber with a function for visualizing the deployment conditions of the telecommunications outside plants.

Silicon nitride (SiN) waveguides with ultra-low optical loss enable integrated photonic applications including low noise, narrow linewidth lasers, chip-scale nonlinear photonics, and microwave photonics. Lasers are key components to SiN photonic integrated circuits (PICs), but are difficult to fully integrate with low-index SiN waveguides due to their large mismatch with the high-index III-V gain materials. The recent demonstration of multilayer heterogeneous integration provides a practical solution and enabled the first-generation of lasers fully integrated with SiN waveguides. However, a laser with high device yield and high output power at telecommunication wavelengths, where photonics applications are clustered, is still missing, hindered by large mode transition loss, non-optimized cavity design, and a complicated fabrication process. Here, we report high-performance lasers on SiN with tens of milliwatts output power through the SiN waveguide and sub-kHz fundamental linewidth, addressing all the aforementioned issues. We also show Hertz-level fundamental linewidth lasers are achievable with the developed integration techniques. These lasers, together with high-Q SiN resonators, mark a milestone towards a fully integrated low-noise silicon nitride photonics platform. This laser should find potential applications in LIDAR, microwave photonics and coherent optical communications., Achieving high output power and low noise integrated lasers is a major challenge. Here the authors experimentally demonstrate integrated lasers from a Si/SiN heterogeneous platform that shows Hertz-level linewidth, paving the way toward fully integrating low-noise silicon nitride photonics in volume using real devices for lasing.

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

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

Semiconductor lasers are widely used in incoherent/coherent optical communications, optical fiber sensing, and lidar due to their small size, high efficiency, and immunity to vibrations. To support the continuous evolution of these high-performance application systems, the noise characteristics of semiconductor lasers play a key role and the noise levels need to be reduced to unprecedentedly low values (such as quantum limit). In this paper, a comprehensive overview on the principles, measurements, and suppressions of semiconductor laser noises are provided. First, we introduce the analysis models and key performance indicators of semiconductor lasers related to noise. Then, different noise measurement systems are investigated for semiconductor lasers and the noise characteristics are fully analyzed. Next, the noise suppression methods towards semiconductor lasers are demonstrated from three aspects: the chip structures, the external cavity optical feedback technology and the driving and controlling circuits. Finally, we summarize the recent advances on the noise measurement and suppression of semiconductor laser, future prospects are also discussed.

In this paper we propose and numerically study a neuromorphic computing scheme that applies delay-based reservoir computing in a laser system consisting of two mutually coupled phase modulated lasers. The scheme can be monolithic integrated in a straightforward manner and alleviates the need for external optical injection, as the data can be directly applied on the on-chip phase modulator placed between the two lasers. The scheme also offers the benefit of increasing the nodes compared to a reservoir computing system using either one laser under feedback or laser under feedback and optical injection. Numerical simulations assess the performance of the integrated reservoir computing system in dispersion compensation tasks in short-reach optical communication systems. We numerically demonstrate that the proposed platform can recover severely distorted 25 Gbaud PAM-4 signals for transmission distances exceeding 50 km and outperform other competing delay-based reservoir computing systems relying on optical feedback. The proposed scheme, thanks to its compactness and simplicity, can play the role of a monolithic integrated hardware accelerator in a wide range of application requiring high-speed real-time processing.

Optical fiber communication has developed rapidly because of the needs of the information age. Here, the variable coefficients fifth-order nonlinear Schrodinger equation (NLS), which can be used to describe the transmission of femtosecond pulse in the optical fiber, is studied. By virtue of the Hirota method, we get the one-soliton and two-soliton solutions. Interactions between solitons are presented, and the soliton stability is discussed through adjusting the values of dispersion and nonlinear effects. Results may potentially be useful for optical communications such as all-optical switches or the study of soliton control.

Spatiotemporal mode-locked (STML) fiber lasers attract great interest owing to their distinctive spatiotemporal characteristics and potential to generate high-energy pulse. Herein, we report an all few-mode fiber figure-eight laser STML by a nonlinear amplifying loop mirror at 1.0 µm. The laser can generate single and multiple pulses at different central wavelengths. In particular, various types of bound-state solitons, such as conventional bound-state solitons and double bound-state solitons, are also achieved and further confirmed by the numerical simulations. The obtained results contribute to further understanding the nonlinear characteristics of STML fiber lasers and such a laser has potential applications in optical communications, especially in information coding.

Optical detection is the basic underlying principle of many optoelectronic systems like image sensors, optical communications, biomedical imaging, motion detection, surveillance, machine vision, etc. Applied research in optoelectronics has invested a lot towards the development of photodetectors with a wide spectral response (UV, visual and IR), as well as narrowband spectrum selective photodetectors for special applications. Spectral discrimination is required for colour-selective detection, but current commercial systems use broadband photodetectors combined with optical filters. This approach increases the complexity of the system and degrades the quality of colour detection. In this article, we explain briefly the basics of photodetectors and a method for tuning the spectral response to achieve filter-free, narrowband photodiodes.

The evolution from analog to digital must be comprehended and specially the implications of the digital world in terms of adaptation of the telecommunication systems. This chapter covers the propagation characteristics of specific telecommunication technologies, that is, optical fiber communications and radiocommunications. The very foundations of telecommunications are the transmission of signals from one point to another. A signal is a mathematical representation of the evolution of a physical quantity concerning some parameters. The main advantage of the Fourier Transform is the opportunity of looking at a signal from the frequency dimension. In telecommunications and computer networks, multiplexing is a method by which multiple analog or digital signals are combined into one signal over a shared medium. Channel Coding is a technique used in digital communications that is focused on the reduction of errors in the receiver side of the systems. Optical communications are based on the transmission of light pulses instead of electrical signals.

The continuing development of consumer electronics, mobile communications and advanced computing technologies has led to a rapid growth in data traffic, creating challenges for the communications industry. Light-emitting diode (LED)-based communication links are of potential use in both free space and optical interconnect applications, and LEDs based on emerging semiconductor materials, which can offer tunable optoelectronics properties and solution-processable manufacturing, are of particular interest in the development of next-generation data communications. Here we review the development of emerging LED materials—organic semiconductors, colloidal quantum dots and metal halide perovskites—for use in optical communications. We examine efforts to improve the modulation performance and device efficiency of these LEDs, and consider potential applications in on-chip interconnects and light fidelity (Li-Fi). We also explore the challenges that exist in developing practical high-speed LED-based data communication systems. This Review examines the development of emerging semiconductor materials—organic semiconductors, colloidal quantum dots and metal halide perovskites—for light-emitting diodes, considering efforts to improve modulation performance and device efficiency, as well as potential applications in on-chip interconnects and light fidelity (Li-Fi).

In this tutorial, we discuss the evolution of the technology deployed for optical interconnects and the trade-offs in the design of low complexity, low power DSP and implementation for direct detect and coherent, pluggable optical modules for data center applications. The design trade-offs include the choice of modulation format, baud rate, optical link design, forward error correction, signal shaping and dispersion compensation.

In this paper, we investigate the performance of a mixed radio-frequency-underwater wireless optical communication (RF-UWOC) system where an unmanned aerial vehicle (UAV), as a low-altitude mobile aerial base station, transmits information to an autonomous underwater vehicle (AUV) through a fixed-gain amplify-and-forward (AF) or decode-and-forward (DF) relay. The analysis accounts for the main factors that affect the system performance, such as the UAV height, air bubbles, temperature gradient, water salinity variations, detection techniques, and pointing errors. Employing the fixed-gain AF and DF relays, expressions for some key performance metrics are derived, e.g., outage probability (OP), average bit error rate (ABER), and average channel capacity. Moreover, in order to get further insights, asymptotic analyses for the OP and ABER are also carried out. Additionally, for the two relaying systems, we derive analytical expressions for the optimal UAV altitude that minimizes the OP. Simulation results show that the UAV altitude influences the system performance and there is an optimal altitude which ensures a minimum OP. Furthermore, it is demonstrated that the diversity order of the fixed-gain AF relaying depends on the RF link and pointing errors, while the diversity order of the DF relaying depends on the detection techniques and pointing errors.

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.

One of the main directions in the development of optical communication systems is associated with the use of optical fiber (ОF) for data reception and transmission. Therefore, manufacturers began to pay special attention to the creation of new brands of OF, improving their optical and operational characteristics. This makes it possible to improve existing optical fiber components that use OF as an active medium. The most widely used are two-wavelength 1 × 2 WDM multiplexers/demultiplexers designed to separate and combine optical carriers with wavelengths of 1310 and 1550 nm, corresponding to the second and third transparency windows of quartz OF. It should be noted that multiplexers and demultiplexers are the same optical devices, which are spectrally selective splitters. Such devices are distinguished by a sufficiently high level of optical characteristics at a relatively low cost of products. However, an analysis of the multiplexers produced in recent years shows that the characteristics of these devices do not sufficiently correspond to the set of modern requirements imposed by most system developers, in particular on permissible values of external influencing factors, insertion loss and the value of optical isolation of channels. Therefore, the development and research of WDM multiplexers with improved optical characteristics is relevant. One of the possible ways of optimizing such devices using new types of OF with resistance to bending losses, of which WDM multiplexers could be made. In this paper, we consider the possibilities of realizing fused single-mode multiplexers/demultiplexers based on combined fiber structures. The technology and equipment for the manufacture of these devices are presented. The optical characteristics of experimental samples of WDM multiplexers are investigated. The results of testing for the effect of temperature are given.

A bidirectional white-lighting wavelength-division-multiplexing (WDM) visible light communication (VLC)–underwater wireless optical communication (UWOC) converged system with an office-level white light illumination of 514 lux and a symmetric downstream/upstream data rate of 150 Gb/s is demonstrated successfully. Red, green, and blue (RGB) laser diodes with two-stage light injection and optoelectronic feedback schemes are operated to provide bidirectional acceptable office-lighting and high-transmission-rate. White light is created/separated by combining/dispersing RGB lights utilizing two cascaded transmission gratings at the transmitting/receiving side. By employing PAM4 modulation and RGB triple-light WDM technique, the transmission rate is enhanced remarkably to 150 Gb/s for downlink/uplink transmission. Acceptable office-lighting (>500 lux) is attained through 3 m plastic optical fiber transport. Additionally, good bit error rate performance of 10−9 and accepted PAM4 eye diagrams are obtained over 10 m free-space transmission with 5 m ocean underwater link. The bidirectional white-lighting WDM VLC–UWOC converged system demonstrated here is beneficial for the development of white-lighting with high-speed optical wireless communications.

Microscale lasers efficiently deliver coherent photons into small volumes for intracellular biosensors and all-photonic microprocessors. Such technologies have given rise to a compelling pursuit of ever-smaller and ever-more-efficient microlasers. Upconversion microlasers have great potential owing to their large anti-Stokes shifts but have lagged behind other microlasers due to their high pump power requirement for population inversion of multiphoton-excited states. Here, we demonstrate continuous-wave upconversion lasing at an ultralow lasing threshold (4.7 W cm−2) by adopting monolithic whispering-gallery-mode microspheres synthesized by laser-induced liquefaction of upconversion nanoparticles and subsequent rapid quenching (“liquid-quenching”). Liquid-quenching completely integrates upconversion nanoparticles to provide high pump-to-gain interaction with low intracavity losses for efficient lasing. Atomic-scale disorder in the liquid-quenched host matrix suppresses phonon-assisted energy back transfer to achieve efficient population inversion. Narrow laser lines were spectrally tuned by up to 3.56 nm by injection pump power and operation temperature adjustments. Our low-threshold, wavelength-tunable, and continuous-wave upconversion microlaser with a narrow linewidth represents the anti-Stokes-shift microlaser that is competitive against state-of-the-art Stokes-shift microlasers, which paves the way for high-resolution atomic spectroscopy, biomedical quantitative phase imaging, and high-speed optical communication via wavelength-division-multiplexing., Upconversion microlasers present a lot of advantages but also require high pumping powers. Here the authors present a high-performing microlaser based on anti-Stokes-shift in upconversion nanoparticles synthesized using a technique of liquid quenching.

Optical fiber Bragg gratings (FBGs) featured with narrowband transmission dips (or reflection peaks) have been maturely employed in technologies of optical communications, lasers and sensors. Here, we report a simple strategy to control the lineshapes of FBG's transmission dip by inserting the FBG in one arm of an all-fiber Mach-Zehnder interferometer (MZI). The transmission dip could be modulated into an asymmetric Fano-like lineshape or a transmission peak, which is controlled by the phase difference between the two arms of the MZI. It works for the uniform, chirped, and phase-shifted FBG. We experimentally verify it with a uniform FBG, showing freely modulated asymmetric Fano-like lineshape with the optical delay line, strain and temperature. Due to the modulation, the maximal slope rate is 49.1 dB/nm, and the Fano parameter q can be tuned from -∞ to +∞. The tunable lineshapes of the FBGs might open up a new window for the applications of traditional FBGs in lasers, communications and sensors.

We numerically demonstrate a feasible way to generate a high-repetition-rate ultrashort soliton train from a dual frequency beat signal on a chip-scale silicon waveguide. A train of well-separated solitons is formed in the designed novel tapered silicon waveguide. Through the self-similar pulse compression, the pulse duration of the input pulse train is compressed from 1.5625 ps to 123.4 fs at the telecomm wavelength. Besides, the pulse propagation consists of two stages: pulse shaping and pulse compression, where the raised-cosine pulse train is evolved into the hyperbolic secant pulse train and further realize an efficient self-similar compression. The results deepen our understanding of nonlinear propagation in silicon waveguides, and open the possibility of high-repetition-rate pulse trains functionalities for ultrahigh-capacity optical communication and micro-machining in a monolithic CMOS platform.

Data rates in optical fiber networks have increased exponentially over the past decades and core-networks are expected to operate in the peta-bit-per-second regime by 2030. As current single-mode fiber-based transmission systems are reaching their capacity limits, space-division multiplexing has been investigated as a means to increase the per-fiber capacity. Of all space-division multiplexing fibers proposed to date, multi-mode fibers have the highest spatial channel density, as signals traveling in orthogonal fiber modes share the same fiber-core. By combining a high mode-count multi-mode fiber with wideband wavelength-division multiplexing, we report a peta-bit-per-second class transmission demonstration in multi-mode fibers. This was enabled by combining three key technologies: a wideband optical comb-based transmitter to generate highly spectral efficient 64-quadrature-amplitude modulated signals between 1528 nm and 1610 nm wavelength, a broadband mode-multiplexer, based on multi-plane light conversion, and a 15-mode multi-mode fiber with optimized transmission characteristics for wideband operation., Space division multiplexing solutions are one way to increase future fiber information capacity. Here, the authors show peta-bit/s transmission in a standard-diameter, multimode fiber enabled by combining several practical multiplexing technologies.

The development of optical fiber technology has facilitated the technological innovation in optical fiber communication and sensing systems over the past decades. Among all the fiber sensing technologies, distributed optical fiber sensing (DOFS) has attracted great research interests and has been extensively investigated. In optical fiber communication systems, optical parameters such as intensity, phase, polarization, or frequency are modulated to realize data transmission, while for DOFS they are employed to measure the distributed physical parameter variation along the sensing fiber. Due to the similarities shared by optical fiber communication systems and DOFS systems, optical communication techniques, including coherent detection, polarization diversity and multicarrier signaling have been widely used in the DOFS to improve the sensing performance. In this article, principles of coherent detection, polarization diversity and multicarrier signaling are introduced and their applications in phase sensitive optical time domain reflectometry and Brillouin optical time domain analyzer are reviewed. A newly proposed unidirectional forward transmission based DOFS is also presented.

Vortex beams have attracted much attention in recent years due to unique features of the phase or polarization singularity in the center part of beams. Various applications have been explored by the vortex beams including optical communication, optical tweezer, etc . Especially, the vortex beams for optical sensing applications have emerged. Compared with the traditional Gaussian beams, the vortex beams enable the optical sensing with the degree of freedom by controlling the spin and orbital phase and polarization. In this review article, we have discussed the theory of polarization and phase vortices, and then summarized the vortex beam generation in optical fiber and their sensing applications. It is hoped that the article can intrigue further research interest and development in fiber vortices for sensing applications.

Vectorial holography has gained a lot of attention due to the promise of versatile polarization control of structured light for enhanced optical security and multi-channel optical communication. Here, we propose a bifunctional metasurface which combines both structural color printing and vectorial holography with eight polarization channels towards advanced encryption applications. The structural colour prints are observed under white light while the polarization encoded holograms are reconstructed under laser illumination. To encode multiple holographic images for different polarization states, a pixelated metasurface is adopted. As a proof-of-concept, we devise an electrically tunable optical security platform incorporated with liquid crystals. The optical security platform is doubly encrypted: an image under white light is decrypted to provide the first key and the corresponding information is used to fully unlock the encrypted information via projected vectorial holographic images. Such an electrically tunable optical security platform may enable smart labels for security and anticounterfeiting applications., The authors present a bi-functional metasurface, combining structural color printing observed under white light and polarization encoded It is appropriate. vectorial holography. A pixelated design is used encode multiple holographic images, and they demonstrate an electrically tunable optical security platform.

Electro-optic modulation based on a graphene nanoelectromechanical system (NEMS) with superlubricity is proposed and systematically theoretical investigated. We demonstrate that the superlubricity greatly improve the performance of photoelectric modulators based on graphene NEMS due to its extremely low coefficient of friction. The modulation voltage of graphene NEMS electro-optic modulation with superlubricity can be reduced to 200 mV, which is 1–3 orders of magnitude larger lower than that of the traditional electro-optical modulator, giving rise to a dramatic reduction of the power consumption of the modulator by approximately 3 orders of magnitude. The modulation response speed can reach nanoseconds, which is 4 orders of magnitude higher than the speed of traditional mechanical electro-optic modulation. At the same time, this modulator has a very wide modulation wavelength range and is not sensitive to the angle of incident light. Two-dimensional material devices, incorporated with mechanical modulation and superlubricity, will have important applications in optoelectronics and optical communication.

In order to generate high quality regular optical vortex array (OVA), we present an experimental method for generating OVA using phase only liquid crystal spatial light modulator (LC-SLM) assisted two gratings. In the scheme, holograms of two grating are displayed on the screen of two LC-SLMs respectively; the diffraction optical fields are captured by a CCD camera. The simulated and experimental results show that the regular OVA can be generated by using double diffraction gratings. The generated OVAs have a constant topological charge of ±1. The method can provide a useful pathway to produce regular OVA for some applications in optical communication, particle trapping and optical metrology.

Microresonators show great potential as interlayer routing solutions for multilayered three-dimensional (3D) photonic communication networks. New techniques are needed for the convenient and in situ manipulation and immobilization of glass microspheres into functional structures. Herein, near-infrared (NIR) and ultraviolet (UV) lasers were used as optical tweezers to precisely arrange silica microspheres and UV-initiated immobilization in a 3D space. The NIR laser was used to trap targeted microspheres, and the UV laser was focused to immobilize the trapped microspheres in 3-methacryloxypropyltrimethoxysilane (MOPS) in ∼6 s. Optical force spectroscopy was performed using the optical tweezers to measure individual bond strength. Next, functional triangular pedestals were designed to flexibly control the gap space for vertical router applications in 3D photonic networks. Thus, the designed UV–NIR dual-beam optical tweezer system can be used to assemble arbitrary functional 3D structures, making it a valuable tool for microfabrication, photonics, and optical communication applications.

The transfer matrix method (TMM) is deployed to determine the reflectance spectra of Octonacci photonic structures. First, the structures are designed using the TiO2 and SiO2 slabs materials. This design allows the obtainment of limited high reflectors for some optical communication wavelengths and for both TE and TM polarizations. After that, the superconductor YBa2Cu3O7 (YBCO) and the silica slabs replace the previous materials in Octonacci structures. This modification permits to extend the omni-directional reflectance bands for both polarizations. The iteration number of the Octonacci sequence has an important effect on these bands. Later the geometric thickness of the photonic structure is optimized by changing the reference wavelength λ0 and omnidirectional high reflectors that cover all optical communication wavelengths (650, 850, 1300 and 1550 nm) are obtained. In addition, for these wavelengths, a tiny effect of the ambient temperature is noticed. These omnidirectional high reflectors can find application in glass (GFO) and plastic (PFO) fiber optics and may be used in sensing applications.

We report the design and fabrication of a high-speed GeSn normal-incidence p-i-n photodetector. To realize high-speed detection in all telecommunication bands, we optimize the Sn content in the absorption layer, the absorption-layer thickness, and the device size. The responsivity of the 18-μm-diameter device at 1550 nm reaches 0.32 A/W with an extended cutoff wavelength of 1700 nm and a 3-dB bandwidth as high as 28 GHz under −3 V bias, clear open eye diagrams are also obtained under zero bias at 1630 nm. All the results indicate that the device has a significant potential for applications in Si-based optical telecommunication in all telecommunication bands.

In this paper we present a review focused on Space Division Multiplexing (SDM) technology. A summary of the most recent works on innovation in the efficiency of SDM as well as its application in data transmission is described. SDM is a technology that has improved the capacity of optical communication systems. Combined with other optical technologies has significantly increased the capacity of information that is sent through an optical fiber.

The existing pulsed laser technologies and devices are mainly in the infrared spectral region below 3 μm so far. However, longer-wavelength pulsed lasers operating in the deep mid-infrared region (3-20 μm) are desirable for atmosphere spectroscopy, remote sensing, laser lidar, and free-space optical communications. Currently, the lack of reliable optical switches is the main limitation for developing pulsed lasers in the deep mid-infrared region. Here, we demonstrate that topological semimetal antimonene possesses an ultrabroadband optical switch characteristic covering from 2 μm to beyond 10 μm. Especially, the topological semimetal antimonene shows a very low saturable energy fluence (only 3-15 nJ cm-2 beyond 3 μm) and an ultrafast recovery time of ps level. We also demonstrate stable Q-switching in fiber lasers at 2 and 3.5 μm by using topological semimetal antimonene as passive optical switches. Combined with the high environmental stability and easy fabrication, topological semimetal antimonene offers a promising optical switch that extends pulsed lasers into deep mid-infrared region.

Optical communication either in free space wireless mode or optical fiber mode is much preferred for high data transmission rate in the range of 100 GHz or few THz. Implementation of OFDM in fiber helps to simplify the dispersion compensation but nonlinearity in fiber material will become a major challenge. This Chapter is review and literature survey about the development and possibilities for OFDM in optical fiber communication systems. It presents the basic features of OFDM and its impact on the mitigation of optical fiber impairments.

Optical fiber sensing technology has developed rapidly since the 1980s with the development of the optical fiber and fiber optical communication technology. It is a new type of sensing technology that uses light as a carrier and optical fiber as a medium to sense and transmit external signals (measurands). Distributed fiber optical sensors (DFOS) can continuously measure the external physical parameters distributed along the geometric path of the optical fiber. Meanwhile, the spatial distribution and change information of the measured physical parameters over time can be obtained. This technology has unmatched advantages over traditional point-wise and electrical measurement monitoring technologies. This paper summarizes the state-of-the-art research of the application of the distributed optical fiber sensing technology in geo-engineering in the past 10 years, mainly including the advantages of DFOS, the challenges in geo-engineering monitoring, related fundamental theoretical issues, sensing performance of the optical sensing cables, distributed optical fiber monitoring system for geo-engineering, and applications of optical fiber sensing technology in geo-engineering.

Optical orbital angular momentum (OAM), carried by optical vortices, is a fundamental property of light that grabs broad interests. The detection of OAM modes, including fractional OAM is of great importance in diverse fields. Here, we firstly propose and develop the limited integer-component measurement method to determine the fractional topological charge (TC) of OAM states. This method indicates that a 2-integer-mode responsive device could be applied for the detection of fractional TC. An orthogonal long-period fiber grating (OLPFG) element is used as a fractional OAM TC probe to verify the Applicability. We experimentally demonstrate the fractional TC detection, ranging from −1 to 0, and recognize different fractional OAM modes with the minimum TC interval of 0.01. This scheme provides a concise, precise, continuous, and fiber-compatible fractional TC detection method that might have great potential in micro-detection, optical communication, quantum information, and chiral sensing applications.

Few-mode fiber is a significant component of free-space optical communication at the receiver to obtain achievable high coupling efficiency. A theoretical coupling model from the free-space optical communication link to a few-mode fiber is proposed based on a scale-adapted set of Laguerre-Gaussian modes. It is found that the coupling efficiency of various modes behaves differently in the presence of atmospheric turbulence or random jitter. Based on this model, the optimal coupling geometry parameter is obtained to maximize the coupling efficiency of the selected mode of few-mode fiber. The communication performance with random jitter is investigated. It is shown that the few-mode fiber has better bit-error rate performance than single-mode fiber, especially in high signal-to-noise ratio regimes., 8 pages, 8 figures

Self-powered ultraviolet photodetectors offer great potential in the field of optical communication, smart security, space exploration, and others; however, achieving high sensitivity with maintaining fast response speed has remained a daunting challenge. Here, we develop a titanium dioxide-based self-powered ultraviolet photodetector with high detectivity (≈1.8 × 10

Recently discovered extraordinary optical nonlinearities in epsilon-near-zero (ENZ) materials open a new realm of ultra-energy-efficient, all-optical switching devices for future optical communication and computation. In this paper, we propose a sub-micron, sub-pico-second, femto-joule level all-optical switch (AOS) using hybrid plasmonic-silicon waveguides driven by high mobility transparent conductive oxides (HMTCOs) such as cadmium oxide. Our analysis indicates that the ENZ-induced nonlinear optical effect is greatly enhanced by the high free carrier mobility in the telecom wavelength region. We propose an electrically tunable AOS device which is precisely biased at the ENZ condition, or the high-loss “OFF” state. Then the AOS device can be switched to the “ON” state with an unprecedented modulation strength of 15.9 dB/μm and a rapid switching time of 230 fs at the cost of an ultralow switching energy of 13.5 fJ. By defining a comprehensive metric using the product of device size, switching energy and switching time, the proposed ENZ-enabled device shows superior performance than any existing on-chip AOS device. We envision that such HMTCO-driven AOS device can be integrated with silicon photonic integrated circuits to realize on-chip optical signal processing and computation with ultra-low energy and ultra-high bandwidth.

Orbital angular momentum (OAM) of light provides a new dimension to increase the communication capacity. The compact and miniaturized devices are preferred because of the advantages in reliability and easy integration. In this work, a quarter-ring-shaped phase-gradient metasurface (QR-PGM) is proposed to sort various propagating waves into fully separated waveguide channels according to their OAM states. The principle is based on focal spot shifting arising from the constructive interference of surface plasmon polaritons with azimuthal phase modulated by the vortex beam. A thorough analysis of the SPP focusing properties was also carried out, which suggests the superiority of quarter-circular arc in OAM sorting (compared with half-circular arc). Focusing efficiency of the QR-PGM reaches to 25%, owing to dense sampling of incident light and unidirectional excitation of SPPs. By coupling spots to waveguides, the wide band on-chip sorting was demonstrated. In the broad wavelength band from 1.3 to 1.6 μm, the extinction ratio of each waveguide port keeps above 3 dB. The proposed structure is compact, efficient, wavelength-division-multiplexing-compatible, and easy to integrate with other on-chip devices. It will be a promising element for high capacity optical communication systems.

Driven by narrow-linewidth bench-top lasers, coherent optical systems spanning optical communications, metrology and sensing provide unrivalled performance. To transfer these capabilities from the laboratory to the real world, a key missing ingredient is a mass-produced integrated laser with superior coherence. Here, we bridge conventional semiconductor lasers and coherent optical systems using CMOS-foundry-fabricated microresonators with record high $Q$ factor over 260 million and finesse over 42,000. Five orders-of-magnitude noise reduction in the pump laser is demonstrated, and for the first time, fundamental noise below 1 Hz$^2$ Hz$^{-1}$ is achieved in an electrically-pumped integrated laser. Moreover, the same configuration is shown to relieve dispersion requirements for microcomb generation that have handicapped certain nonlinear platforms. The simultaneous realization of record-high $Q$ factor, highly coherent lasers and frequency combs using foundry-based technologies paves the way for volume manufacturing of a wide range of coherent optical systems., Comment: 19 pages, 11 figures

In power-limited trans-oceanic submarine systems, the electrical-to-optical (E/O) power conversion efficiency determines the amount of optical signal power generated by repeaters, which governs the cable capacity. In contrast to conventional submarine systems, recent single mode fiber spatial division multiplexing (SDM) systems operate at a lower channel power and support a larger number of optical fibers. Moreover, pump sharing technology is used in SDM systems to enhance cable capacity and system reliability, where a group of pump lasers are combined to feed a group of fiber pairs. The repeater E/O power conversion efficiency is directly related with cable capacity, as well as capacity per power and cost per capacity analysis. Therefore, it is important to understand the characteristics of repeater E/O efficiency. We developed a model to analyze the repeater E/O efficiency in submarine SDM systems. Experimental measurement data of pump lasers and numerical simulation results of Erbium doped fiber amplifiers (EDFAs) were used as input information to the model to analyze repeater E/O efficiency in various system designs. Based on the E/O efficiency model results, we investigated cable capacity using the Gaussian noise (GN) model. Moreover, cable capacity per power was calculated and compared based on three different power metrics: (i) electrical supply power, (ii) pump optical power and (iii) EDFA output power. With the aid of the repeater E/O efficiency model, one can analyze the efficiency of submarine systems using the direct metric of cable capacity per electrical supply power.

This paper designs a 1 × 2 switchable dual-mode optical 90° hybrid device on the silicon-on-insulator (SOI) platform for the mode division multiplexing hybridized coherent transmission systems in optical communication. Our proposed hybrid uses various 2 × 2 multimode interference (MMI) couplers, symmetric Y-junctions, and thermo-optic phase shifters. The suggested hybrid device working principle is proved on theoretical analysis about the multimode interference and the transfer matrix relation. The optimization of geometrical parameters and metallic micro-heaters is executed through the numerical simulation method. The proposed hybrid coupler expresses lots of optical performance advantages, with an insertion loss lower than 2.5 dB, a common-mode rejection ratio (CMRR) better than −24 dB, and phase error smaller than 4° in the 50-nm wavelength bandwidth of the third telecom window for both two TE modes. Besides, the device is proven large geometrical tolerances in terms of width and height tolerances larger than ±50 nm and ±6 nm in the 1.5-dB variation limit of transmission, respectively. In addition, the proposed device attains relatively low power consumption under 75 mW and an ultrafast switching time below 10 μs. Such advantages of good performances make the device a promising potential for broadband and intra-chip MDM-hybridized coherent optical communication systems and photonic integrated circuits.

This work utilizes the modified Attenuated Total Reflection (ATR) configuration, to detect minute refractive index changes near the sensing surface. In the proposed ATR configuration, the presence of the graphene layer increases the interaction with bio-analyte by adsorbing the biomolecules and the presence of a thin silicon layer helps to enhance the sensitivity of the proposed device. The use of aluminum as the plasmonic metal serves an economical value as well as compatibility with the optoelectronic devices. All the geometrical parameters of the layers over the base index prism are engineered for maximum sensitivity and narrow linewidth in the optical communication band using the transfer matrix method. The stacking of silicon-graphene layers over the thin metal-coated glass prism leads to the maximum sensitivity of 200°/RIU and figure of merit of 95.23 RIU−1 at the wavelength of 1550 nm. To demonstrate the proposed device as a bio-sensor, rodent urine is considered as the analyte under test to detect the changes in the varying concentration of Leptospira bacterium. The proposed plasmonic device opens a new window for the detection of biomolecular interactions in the optical communication band.