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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.

With high-speed space optical crosslink being a reality, the construction of an optical satellite network as part of a larger integrated space-terrestrial network is now feasible. This paper explores the architecture implications of the invention of such a radical technology building block. Not only can the satellite network performance and cost undergo quantum-leap improvements but also such a network can have profound transforming effects on space system architectures and data network user applications.

In this work, a modified square photonic crystal fiber (MS-PCF) architecture is exposed with ultra-high negative dispersion for communication window. The validation of the model is successfully performed by applying an efficient full-vector finite element method (FV-FEM) with anisotropic perfectly matched layers (PMLs) for precise simulation of PCFs. Additionally, waveguide dispersion engineering is accomplished by tuning the structural parameters of the MS-PCF. From the numerical investigation, negative dispersion behavior permits remarkable suppression rather than positive dispersion. It offers the high negative dispersion of −2357.54 ps/nm/km and Kerr nonlinearity (γ) of 74.68 W−1 km−1 simultaneously at the operating wavelength, λ = 1550 nm. Nevertheless, the designed fiber ensures the mono mode operation in the entire band of interest from λ = 1340 nm to λ = 1580 nm. MS-PCF with these outstanding optical performances has distinguished potency to be practiced as a dispersion compensating fiber in optical communication systems.

Optical communication has been employed in a wide range of applications, including the terrestrial, submarine, inter-satellite, and even space communication. It is particularly successful in fiber-based communication networks that vastly reshape modern life through the Internet. With the intensified activities such as undersea resource exploration, ecosystem monitoring, and recreation, underwater is an exciting new arena for optical wireless communication (OWC). In this paper, we review the recent progress of underwater and water-air OWC systems. Channel characterization, communication system design, and performance investigations are given. Critical limitations and effective mitigation methods to overcome the influence of bubbles and waves are presented. We also address the current issues for proper performance comparison under different wave conditions. With further research in channel modeling, device innovation, and system design optimization, practical and robust underwater and water-air OWC systems can be realized.

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.

Low noise optical amplifiers play a vital role in optical communications and signal processing. Recently, there has been a pursuit for compact, waveguide-based, parametric amplifiers which employ the four-wave mixing process relying on the 3rd order nonlinearity, (3), of the material. Here, we present an analytic model for the gain and noise of phase-sensitive parametric amplifiers based on nonlinear optical waveguides, which includes the impact of the linear loss of the waveguide. We provide insights into the importance of this loss for the gain, but more importantly also for the amplifier noise figure. In particular, we study waveguides based on Si3N4 and find that a gain of 28 dB with a 0.8 dB noise figure is feasible in a 3 m long waveguide having a loss of 1.5 dB/m. We finally investigate the impact of the Si3N4 waveguide cross section on the dispersion and the nonlinear coefficient for the improvement of PSA performance.

A novel VCSEL array for high-efficiency, high-speed, and high-brightness performance is demonstrated. In contrast to the traditional VCSEL arrays, which have several independent VCSEL cavities in parallel, the novel array structure has additional passive optical waveguides connecting each cavity. In addition, Zn-diffusion and oxide-relief structures are adopted for each single element of the array to obtain the high-brightness (single-mode; SM) output and relax the RC-limited bandwidth. Comparison is made to the traditional reference array. Although the values of the oxide-relief apertures are close to each other, the novel demonstrated arrays exhibit a higher wall plug efficiency, larger maximum output power, and better eye-opening for high-speed data transmission, when both of their output optical spectra are quasi-(SM) with close narrow divergence angle values (FWHM: ∼6°). The superior performance of the demonstrated array for (quasi-) SM operation can be attributed to the dilution of the photon density in the SM output pattern from each VCSEL unit through the connections of passive waveguide. Furthermore, it also enhances the coherence between the neighboring VCSEL emitters, minimizing their interference noise which occurs under large signal modulation. This novel 940 nm VCSEL array has good potential to serve as a light source in free-space optical communication.

We present a numerical analysis of noise performance improvement of the erbium-doped fiber amplifier by flatting the mode field intensity distribution within the interaction region of erbium ions. Three different refractive index types of erbium-doped fiber were used to study the effect of the pump mode intensity distribution on noise performance. The results show that taking advantage of the depressed refractive index erbium-doped fiber which has a flat mode distribution in the fiber core, the maximum reduction of nearly 0.53 dB for noise figure was achieved across the full C-band. Based on the center depressed refractive index profile, the noise figure was further decreased by about 0.1 dB by reducing the doping radius to 0.71 μm. Finally, maintaining the same gain level of ∼38.3 dB, a NF reduction of ∼0.63 dB was realized by introducing the center depressed refractive index profile and narrowing the erbium doping region. It is suggested that our investigation shows great potential for improving the noise performance of the erbium-doped fiber amplifier.

Pulse position modulation (PPM) is a key technology for deep space optical communication (DSOC) system to improve the data transmission rate. To reach optimum rate, the modulation parameters of PPM are required to be analyzed. The rate can be improved by choosing appropriate modulation orders and the initial pulse width. In this paper, the meteorological statistical data of our experimental location are analyzed. Then, the analysis formula of the cloud scattering and atmospheric turbulence influence on PPM communication rate are given. The cloud particles are measured through aircraft detector, simulation analysis is carried out by using the measured data of aircraft detector. Finally, the influence on the communication rate of different cloud physical thickness are analyzed.

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.

Vertical cavity surface emitting laser VCSEL is currently the main solution for many technological aspects, ultrafast optical interconnecting, Gigabit Ethernet, etc. In this paper we present the simulation results by using Optiwave™ software version 7, of the effects of optical mode confinement factor on the modulation properties)which inspected by eye diagram of the received signals)of the vertical cavity surface emitting laser VCSEL, with the range (8-20)Gbps of pseudo random bit sequence PRBS. The quality of the VCSEL modulation have been inspected by time domain signals, spectrums and eye diagram. Simulation results appeared an improvement in the characteristics of received bit sequences of (8, 10, 12.5, 16 and 20)Gbps bit rates, represented by the rising the value of quality factor QF (1.77 to 4.81) versus increasing the value of optical mode confinement factor Γ(0.2 to 0.5) respectively, and a decreasing in jitter time of superimposed traces of eye pattern and well opining eye pattern. And in the corresponding, the bit error rates BERs of the received signals have been decreased, with rising the value of mode confinement factor Γ of the laser at constant modulation index and constant temperature of the laser. Also, the VCSEL’s modulation response differences with different bitrates, causes different values of QF and BER for individual value of mode confinement factor Γ.

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.

Recently, Low Earth orbit (LEO) satellite-based systems have attracted tremendous attention and various technologies have been developed for payload miniaturization and optical communications. In addition, mega constellation architectures are expected to be deployed with LEO satellites for global broadband networks. In this paper, we present a thorough analysis of mega constellation architecture in terms of a change in the number of visible satellites and antenna steering capability to investigate the impact of increase in the constellation size and adoption of optical inter-satellite links (ISLs). The network architecture is evaluated with respect to satellite antenna steering capability and the satellite visibility considering the very narrow beam divergence of optical communications. We analyze the impact of a change in relative positions among the satellites due to continuous satellite movement in the constellation. The results offer guidelines for designing a novel visibility matrix using a time-varying satellite topology. This could defuse the problem of conventional studies using fixed visibility matrices. The proposed time-varying visibility matrix achieves better performance than previous pre-assigned links in terms of end-to-end link distance and hop count of LEO satellite networks.

In today’s world, radio receiver system is a prevailing wireless technology in that the major part is Low Noise Amplifier (LNA) which widely used to improve weak signals in many applications with millimeter and radio frequency waves such as optical communication, multimode transceivers and measurement instrumentations. The real drawbacks of LNA is that it fails to maintain specific properties in critical conditions like as minimum power consumption, provide low noise figure, input matching and linearity. Additionally, promoted by various application demands, design methods and control methods must require to improve performance of LNA. The performance of LNA can be improved by adding extra components in basic circuit by proper arrangement for millimeter and radio frequency waves. The review paper provides information about design methodology, optimization techniques and control techniques. The different design of LNA is reviewed and analyzed such as 3-stage near-mm Wave LNA, 5-stage near-mm Wave LNA, common-gate amplifier, shunt-feedback amplifier, Resistor-terminated common-source amplifier, Traditional inductor-less amplifiers, cascode connection and double common source. This review paper also provides the information about design circuit diagram. The performance improvement of LNA can be achieved with the help of different techniques and our review based on optimization and control techniques with parameter tuning. Finally, the direction for the future study is presented based on review analysis of LNA.

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.

Optical communication systems have evolved over the years from simple intensity modulation and direct detection systems to those involving modulation of amplitude, phase, polarization and transverse modal profile. This article provides a brief tutorial review of the different modulation schemes used in the state-of-the-art optical communication systems and the futuristic trends in this direction to improve the data rates and spectral efficiency. The additional challenges with the advanced modulation schemes are discussed and some experimental results related to the demonstration of high-speed communication with such advanced modulation schemes are presented.

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 )

Pockels cell is used for the processing of light in the field of optical communication and information processing. It is used for phase and amplitude modulation of light using polarized light as a carrier signal. A polarized incident light passes through electro-optic material, and by using the nonlinear property of the electro-optic material, the light is modulated as per the requirement. Here a study is done to show the massive reduction in the intensity of central frequency of the carrier light if multi-passing technique (multi-feedback) is adopted. In this paper, the authors show the significant number of passing (feedback) for such reduction in the intensity of central frequency and this number of passing (feedback) considerably increases the power of the sideband frequencies. The whole scheme is supported by MATLAB simulation. As the biasing signal information lies only in the sideband frequency, not in the carrier frequency, indirectly the increase in the power of the sideband frequencies strengthens the modulation information to be sent for communication by the carrier light wave having the central frequencies. This is the reason for increasing the sideband intensity by decreasing the intensity of the central frequency using multi-feedback mechanism.

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.

Hollow-core fibers offer a range of beneficial properties for high-speed optical communication applications, including low latency, low chromatic dispersion and nonlinearity. Based on a system employing a ~5-km span of hollow-core nested antiresonant nodeless fiber (NANF), we demonstrate in this paper, penalty-free Nyquist 4-ary pulse amplitude modulation transmission relative to the back-to-back at 80, 100 and 112 Gb/s over the S+C+L-bands. Furthermore, using multi-carrier direct-detection optical orthogonal frequency division multiplexing, we show that compared to a standard single-mode fiber of a similar length, the NANF exhibits a significantly better bit error rate (BER) performance at 1550 nm and offers more than 20% capacity enhancement. Consequently, up to 138.09-Gb/s capacity has been achieved at a BER threshold of 3.8×10-3 after ~5-km transmission. We conclude that the use of NANF offers a promising solution for achieving simultaneously high capacity and low latency in future short-reach optical interconnects.

Since optical links are easily blocked by obstacles in the environment, they have been considered difficult to directly perform wireless communications. However, reconfigurable intelligent surfaces (RISs), as a new type of digital coding meta-materials, can significantly improve the coverage of optical communication by establishing new links. We propose a controllable multi-branch wireless optical communication system based on optical RISs. By setting up multiple optical RISs in the environment, multiple artificial channels are built to improve the system performance and to reduce the outage probability. In this paper, we investigate three factors affecting channel coefficients, including beam jitter, RIS jitter, and obstruction probability. We derive closed-form probability density function of channel coefficients, asymptotic average bit-error rate (BER), and the outage probability for systems with multiple branches. Our analysis reveals that the probability density function contains an impulse function, which causes irreducible error rate and outage probability floors. Based on our numerical results, the BER and outage probability floor of the multi-branch system are significantly reduced compared with the single direct path system. Therefore, the optical RIS assisted multi-branch wireless communication is a promising solution against obstacles of optical channel.

This paper explores the effects of sunlight on using a low-cost off-the-shelf silicon solar panel as an optical wireless communication (OWC) receiver. A receiver circuit structure has been proposed to maximize simultaneous energy harvesting and data communication performance. An equivalent circuit model of the solar panel for simultaneous energy harvesting and wireless optical communication is discussed. By using the solar panel model, the effects of varying sunlight conditions on the performance of the model as an OWC receiver are estimated. Furthermore, an experimental setup is developed to study the effects and verify the simulated estimations. The experimental setup consists of a 3.5 m wireless optical link with a full Transmission Control Protocol and Internet Protocol (TCP/IP) network stack. The system uses DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) to use the available communication bandwidth efficiently. A 940 nm low-cost off-the-shelf laser device along with an off-the-shelf off-axis-parabolic mirror is used as the transmitter. The maximum user throughput achieved over the air is 28.3 Mb/s while simultaneously harvesting energy using the maximum power point tracking (MPPT) technique. The peak power harvested with simultaneous communication is 4.5 W. The harvested energy is stored in a 38 Wh lithium-ion (Li-ion) battery.

In this article, an antiresonant nodeless hollow core fiber having nested hybrid cladding elements is proposed without having large distance between core and jacket capillary. The presented anisotropic construction (elliptical nesting in circular tube) with optimized curvature factor, strut thickness, and gap between adjacent tubes lead to extremely low loss over wide band compared to existing structures (circular, circular nested, elliptical, elliptical nested). The results show the lowest confinement loss of 0.0007 dB/km at 1.06 $\mu$ m with maintaining a loss of less than 0.003 dB/km over 670 nm (0.90 $\mu$ m to 1.57 $\mu$ m) bandwidth. In addition, the lowest surface scattering loss of 0.01 dB/km is achieved along with better bending stability and effective single mode operation. The proposed fiber may have potential opportunity in optical communication systems for its low-loss transmission over wideband region.

Free-space optical (FSO) systems are able to offer the high data-rate, secure, and cost-efficient communication links required for applications such as wireless front- and backhauling for 5G and 6G communication networks. Despite the substantial advancement of FSO systems over the past decades, the requirement of a line-of-sight connection between transmitter and receiver remains a key limiting factor for their deployment. In this paper, we discuss the potential role of intelligent reflecting surfaces (IRSs) as a solution to relax this requirement. We present an overview of existing optical IRS technologies; compare optical IRSs with radio-frequency IRSs and optical relays; and identify various open problems for future research on IRS-assisted FSO communications.

An ultracompact photonic crystal channel-drop filter based on a square-shaped dual-loop resonator configuration is proposed in this paper. Four coarse wavelength-division multiplexing (CWDM) channels at 1550 nm, 1570 nm, 1590 nm, and 1610 nm can be dropped with high transmission efficiency simultaneously. The device size of the proposed photonic crystal filter can be reduced to about 296 μm2 because the resonator acts as a channel splitter and dropper at the same time. Furthermore, the two cascaded resonator rings have the same dimension parameters, such as lattice constant and rod radius, which facilitates device fabrication. By simply tuning the refractive index of selected phase change material rods, specific dropping wavelengths can be obtained. The proposed phase-change photonic crystal channel drop filter will have important applications in future photonic integrated circuit-based optical communication systems. The device configuration also provides an important reference for the design of reconfigurable photonic switches and routers.

Photonic reservoir computing (RC) enables us to introduce artificial neural networks (ANNs) as a deployable hardware-based processing unit beyond the von Neumann architecture. Its unique approach to consider only the output layer weights as adaptive, reduces training complexity and enables the use of ANNs in time-sensitive areas like optical communications. In this paper, we numerically investigate and evaluate the requirements of a photonic RC using an active silicon micro-ring resonator as a photonic integrated circuit (PIC) based reservoir system to compensate for transmission impairments such as chromatic dispersion and nonlinear effects occurring in optical transmission systems. We compare the performance of this RC with results from digital signal processing using Kramers-Kronig reception of distorted PAM-4 symbols from a 56 GBaud WDM transmission experiment over 100 km uncompensated SSMF.

Optical vortex beams have attracted significant research interest owing to their potential for application in optical communication and imaging. In this study, we demonstrated devices with electric...

Integrated transceivers with electro-optic modulation characteristics are valuable for free-space optical communications and sensing. We propose an AlInGaAs multiple quantum well (MQW) transceiver with electro-optic modulation characteristics over a broad spectral range. Two identical AlInGaAs MQW diodes on a single wafer are used to transmit and receive optical signals and provide obvious electro-optic modulation for broad-spectrum light. The photocurrent modulation ratio reaches 13.9 and 11.3 for white light and 1550 nm infrared light, respectively, with varying bias voltages. The transceiver can identify environmental changes and forward electrical signals with different frequencies in the form of superimposed optical signals.

Underwater wireless optical communication (UWOC) has been proposed to provide high-rate data services by exploiting the ample optical spectra. However, the underwater scenario presents a hostile environment for wireless optical signal propagation due to the various channel effects, such as absorption, scattering and turbulence. Furthermore, link misalignment (LM) between the optical transmitter and receiver caused by the turbulent water waves degrades the achievable system performance. All the aforementioned factors make the information recovery a challenging task for UWOC systems, especially for long-distance data transmissions. In this letter, we introduce a deep learning (DL) based misalignment-robust blind receiver (MBR) to recover the received data in a multiple-input multiple-output (MIMO) UWOC system, where a convolutional neural network (CNN) is used to formulate the signal characteristics in model training, a CNN combiner is utilized for characteristic analysis and combination, and a CNN demodulator is applied to recover the transmitted information. Evaluation results demonstrate that a reliable performance is achievable by the proposed DL-MBR scheme in UWOC scenarios when a relatively large LM occurs.

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.

The performance of directly-modulated lasers (DMLs) is severely impaired by nonlinear behaviour when operating at high symbol rates. We propose a new linearization method for DML-based transmitters which can significantly reduce nonlinearity. This method, named the “Stretched A” (StrA) method, relies on the generation of an approximation to the ideal modulating current that generates a linear optical output waveform. In Part I of this work, the theoretical framework of the proposed method is presented and detailed simulation studies illustrate its implementation and demonstrate the benefits it offers. Although the method is applicable to any type of DML, the simulation studies presented herein focus on optical links based on vertical-cavity surface-emitting lasers (VCSELs) as these comprise the vast majority of short-reach optical links. Part II of this work presents the proof-of-principle experimental demonstration of this new linearization method and discusses its possible implementations using either analog or digital electronics.

The self-collimation of light through Photonic Crystals (PCs) due to their optical properties and through a special geometric structure offers a new form of beam steering with highly optical control capabilities for a range of different applications. The objective of this work is to understand self-collimation and bending of light beams through bio-inspired Spatially Variant Photonic Crystals (SVPCs) made from dielectric materials such as silicon dioxide and common polymers used in three-dimensional printing like SU-8. Based upon natural PCs found in animals such as butterflies and fish, the PCs developed in this work can be used to manipulate different wavelengths of light for optical communications, multiplexing, and beam-tuning devices for light detection and ranging applications. In this paper, we show the optical properties and potential applications of two different SVPC designs that can control light through a 90-degree bend and optical logic gates. These two-dimensional SVPC designs were optimized for operation in the near-infrared range of approximately 800–1000 nm for the 90-degree bend and 700–1000 nm for the optical logic gate. These SVPCs were shown to provide high transmission through desired regions with low reflection and absorption of light to prove the potential benefits of these structures for future optical systems.

An efficient omnidirectional CubeSat data crosslink is imperative to ensure the success of resource-intensive advanced CubeSat missions. In this article, we present a feasibility study of wireless technologies in high-speed CubeSat crosslink design. We study the power consumption, pointing requirement, and antenna requirement of each technology to implement an omnidirectional communicator. We also investigate the performance limit of the state-of-the-art wireless technologies considering the realizable link parameters. The achievable data rate and communication distance are studied thoroughly for different communication systems. The analyses show that an optical communication link is capable of delivering more than two orders of magnitude higher data throughput than that of microwave links in an omnidirectional platform. However, the study shows that due to the size and power restriction, a performance crossover region exists where the performance of a microwave channel exceeds the performance of the optical channel. The crossover distance and crossover data rate are studied thoroughly with different system configurations and modulation formats to assess the maximum reach of wireless technologies in a CubeSat crosslink.

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.

Optical Spatial mode-division multiplexing that exploits the new few-mode fiber (FMF) technology is a promoted solution for the new optical communication systems. We work on the multilayers method of designing the new optical communication systems FMF. These systems suffer essentially from differential mode delay. In this article, we implement the multilayers method of designing an arbitrary fiber profiles with our own Matlab code and we proposed a fiber profile design with a full control of differential mode delay regions in the C-and L-bands, for six linearly polarized modes circulating in FMF with the cited method.

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.

Plasmonic chiral metamaterials have attracted broad research interest because of their potential applications in optical communication, biomedical diagnosis, polarization imaging, and circular dichroism spectroscopy. However, optical losses in plasmonic structures severely limit practical applications. Here, we present the design concept and experimental demonstration for highly efficient subwavelength-thick plasmonic chiral metamaterials with strong chirality. The proposed designs utilize plasmonic metasurfaces to control the phase and polarization of light and exploit anisotropic thin-film interference effects to enhance optical chirality while minimizing optical loss. Based on such design concepts, we demonstrated experimentally optical devices such as circular polarization filters with transmission efficiency up to 90% and extinction ratio >180, polarization converters with conversion efficiency up to 90%, as well as on-chip integrated microfilter arrays for full Stokes polarization detection with high accuracy over a broad wavelength range (3.5-5 μm). The proposed design concepts are applicable from near-infrared to Terahertz regions via structural engineering.

Graphene-based photodetectors have attracted significant attention for high-speed optical communication due to their large bandwidth, compact footprint, and compatibility with silicon-based photonics platform. Large-bandwidth silicon-based optical coherent receivers are crucial elements for large-capacity optical communication networks with advanced modulation formats. Here, we propose and experimentally demonstrate an integrated optical coherent receiver based on a 90-degree optical hybrid and graphene-on-plasmonic slot waveguide photodetectors, featuring a compact footprint and a large bandwidth far exceeding 67 GHz. Combined with the balanced detection, 90 Gbit/s binary phase-shift keying signal is received with a promoted signal-to-noise ratio. Moreover, receptions of 200 Gbit/s quadrature phase-shift keying and 240 Gbit/s 16 quadrature amplitude modulation signals on a single-polarization carrier are realized with a low additional power consumption below 14 fJ/bit. This graphene-based optical coherent receiver will promise potential applications in 400-Gigabit Ethernet and 800-Gigabit Ethernet technology, paving another route for future high-speed coherent optical communication networks., Graphene-based photodetectors have many advantages for applications. Here, the authors demonstrate a high-speed optical coherent receiver for optical communications based on graphene-on-plasmonic slot waveguide photodetectors.

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.

We demonstrate the fabrication of a broadband mode converter (MC) operating at 2 μm waveband based on long-period fiber gratings (LPFGs) written in the two-mode fiber (TMF) by CO2 laser. The proposed MC offers a 10-dB bandwidth of 58 nm, making it suitable for high-speed broad-band optical communication system at 2 μm waveband. The maximum conversion efficiency reaches 98.89% at wavelength of 2 μm. The torsion, strain, bending, and polarization characteristics of the broadband MC were measured experimentally. The torsion sensitivity of the LPFGs was measured to be 1.32 nm/(rad/m) at 2 μm waveband, which was almost three times higher than that of the grating with the same order mode coupling at 1.55 μm waveband. The proposed broadband MC can function as not only a promotion in fiber communication system but also a high sensitivity torsion sensor in fiber sensing system.