Optical Signal Generation Research Articles

Adaptive generation of optical single-sideband signal with dually modulated EML

The optical single sideband (SSB) transmitter based on dual modulation of an electro-absorption modulation laser (D-EML) has attracted considerable attention for its capability of monolithic integration and high output power. A model-based modulation method has been developed recently for generating high-quality optical SSB signals with this D-EML scheme. However, this method requires accurate characterization of the EML’s chirps and pre-compensation for frequency responses of all-optical/electrical components, as well as the path difference between two driving signals. This imposes notable requirements on the transmitter characterization in practical applications. In this paper, we propose an adaptive method to approach the required responses of the pre-compensation filters for this optical SSB transmitter. This method avoids cumbersome device characterization and shows great resilience to the variation of system parameters. By using the proposed adaptive method, we generate a 56 Gb/s optical SSB orthogonal frequency-division multiplexed signal with the sideband suppression power ratio exceeding 21 dB. It is convenient with this method to switch the devices, i.e., directly modulated laser (DML) or electro-absorption modulator (EAM), to be pre-compensated for the optical SSB signal generation. Moreover, this method exhibits good tolerance to the path delay (±15 ps) between DML and EAM, as well as modulation depth. We also successfully transmit this signal over 80 km long standard single-mode fiber.

Microfluidic Chip-Assisted Upconversion Luminescence Biosensing Platform for Point-of-Care Virus Diagnostics.

Epidemics caused by multiple viruses continue to emerge, which have brought a terrible impact on human society. Identification of viral infections with high sensitivity and portability is of significant importance for the screening and management of diseases caused by viruses. Herein, a microfluidic chip (MFC)-assisted upconversion luminescence biosensing platform is designed and fabricated for point-of-care virus detection. Upconversion nanoparticles with excellent stability are successfully synthesized as luminescent agents for optical signal generation in the portable virus diagnostic platform. The relevant investigation results illustrate that the MFC-assisted virus diagnostic platform possesses outstanding performance such as good integration, high sensitivity (1.12 pg mL-1), ease of use, and portability. In addition, clinical sample test result verifies its more prominent virus diagnostic properties than commercially available rapid test strips. All of these thrilling capabilities imply that the designed portable virus diagnostic platform has great potential for future virus detection applications.

Theoretical Demonstration of Improved Performance in Multi-Channel Photonic RF Signals Based on Optical Injection Locking of Optical Comb and Array Lasers

Multi-channel radio frequency (RF) signal generation, facilitated by photonic technology, offers significant potential for generating coherent signals with a high frequency and low phase noise, providing multifunctional capabilities across diverse platforms, including RF and photonic systems. Traditional methods for multi-channel photonic RF signal generation typically entail the integration of diverse optical components, such as filters and amplifiers. However, this integration often results in compromises related to power efficiency, cost-effectiveness, and implementation simplicity. To address these challenges, we propose a novel method for generating multi-channel photonic RF signals based on optical injection locking technology. This approach eliminates the necessity for traditional optical components, leading to a substantial enhancement in the performance of photonic RF signals. We present the design of an optical injection locking-based multi-channel photonic RF signal generation schematic and theoretically evaluate its Signal-to-Noise Ratio (SNR) and eye pattern performance for data modulation using the Lumerical INTERCONNECT simulator. Our results reveal a significant 1.3-dB and 3.6-dB enhancement in SNR for 30-GHz and 60-GHz signals, respectively. Furthermore, we observed an improved communication performance, as evidenced by enhanced eye patterns in 3-Gbps data transmission compared to passive photonic RF signal generation methods.

16QAM optical signal generation scheme based on weighted optimal Euclidean distance.

A two-dimensional signal constellation scheme for binary uniform memoryless source transmission in optical fiber channels is studied in this paper. In geometric shaping (GS), optimization algorithms are usually used to change the overall position of constellation points while maintaining the probability of constellation points unchanged. Different optimization functions are used to allocate the position of constellation symbols, thereby improving constellation performance. A 16 quadrature amplitude modulation (QAM) optical signal generation scheme based on weighted optimal Euclidean distance is proposed in this paper. In order to obtain the best constellation diagram and increase the shaping gain, the weighted optimal Euclidean distance that can minimize the bit error rate (BER) over multiple iterative optimizations is used as the objective function. On the one hand, the proposed 16QAM optical signal generation scheme based on weighted optimal Euclidean distance always outperforms the uniform square 16QAM and the uniform circle 16QAM schemes in the back to back (BTB) transmission. On the other hand, after analyzing the simulation demonstration in a 50GBaud coherent optical communication system over 3000km, results demonstrate that the optical signal to noise ratio (OSNR) performance of this system is better than that of the uniform square 16QAM and the uniform circle 16QAM, which is improved by 0.52dB and 0.85dB, respectively. In addition, the proposed 16QAM system increases the transmission distance by 989km and 741km, respectively, compared to the other two systems. The performance confirms that the proposed novel 16QAM scheme, to the best of our knowledge, can effectively improve the reliability and transmission distance. Therefore, the proposed scheme has a certain development prospect in the future long-distance transmission of high-speed optical fiber communication.

A review on machine learning-powered fluorescent and colorimetric sensor arrays for bacteria identification.

Biosensors have been widely used for bacteria determinationwith great success. However, the "lock-and-key" methodology used by biosensors to identify bacteria has a significant limitation: it can only detect one species of bacteria. In recent years, optical (fluorescent and colorimetric) sensor arrays are gradually gaining attention from researchers as a new type of biosensor. Theycan acquire multiple features of a target simultaneously, form a feature pattern, and determine the bacteria species with the help of pattern recognition/machine learning algorithms. Previous reviews in this area have focused on the interaction between the sensor array and bacteria or the materials used to make the sensors. This review, on the other hand, will provide researchers with a better understanding of the field by discussing fluorescent and colorimetric sensor arrays based on the mechanism of optical signal generation. These sensor arrays will be compared based on the identified species. Finally, we will discuss the limitations of these sensor arrays and explore possible solutions.

Cascaded optically injection-locked semiconductor laser, rate equations analysis, frequency response, and its application for complex optical signal generation.

In this paper, we introduce the concept of the cascaded optically injection-locked (OIL) semiconductor laser and present its novel rate equations. Then, the new locking range for this configuration has been obtained by mathematical demonstration. Subsequently, we modified a new adjustment for the detuning frequencies (Δ f i n j ) of the cascaded OIL system as well as the linewidth enhancement factors (α) values. Utilizing these tunings, improvements in the steady-state photon number and the phase modulation (PM) range become possible. Afterward, we define the generation of the complex optical signal area and extract the transfer function for investigating the frequency response of the cascaded system. The simulations have been performed once with identical α values and once with the various α values in the slave laser (SL) stages. We conclude that these novel proposed adjustments, combined with a strong injection ratio (Rinj) of 15 dB and a high bias current, can significantly broaden the bandwidth near 700 GHz while maintaining the fair gain available up to 180 GHz. Further, the generation of complex optical signal areas has been boosted for high-quality complex modulation applications. Eventually, we exhibit a novel approach for generating different α values in the SL stages by applying managed temperature variations in the experimental setup of the cascaded system, regardless of employing similar SLs.

Distortion managed directly modulated on-off keying signal transmission for 10 Gbps visible light communications using electrical filtration

Abstract In this research, a communication system that uses visible light as a carrier and is designed for high-throughput interior applications. In order to lower the overall system cost, this work uses intensity modulation at the transmitter and direct detection with electrical filtering at the receiver. Various low-pass filtration techniques (Gaussian, Butterworth, Bessel, and Chebyshev) have been proposed in his paper to mitigate the effect of channel distortion in visible light communication (VLC) systems. The achieved transmission range is up to 3 m in addition to the supported data rate of 10 Gbps with a bit error rate of less than 10−9. Simulations are carried out using optisystem software that includes PRBS OOK optical signal generation at LED output in the transmitter, VLC channel, and APD with LPF in the receiver.

Scheme to eliminate the time shift of code edges based on the optimal transmission point of a DP-MZM.

To eliminate the time shift of code edges on a single-sideband (SSB) modulation signal transmission in a radio-over-fiber (RoF) system, a new, to the best of our knowledge, SSB modulation scheme based on an optimal transmission point for a double-parallel Mach-Zehnder modulator (DP-MZM) is proposed. The scheme is based on DP-MZM to realize the separation of the carrier and the +1st-order sideband at the optimal transmission point, and the baseband signal modulates the 2.5Gb/s data signal to the +1st-order sideband of the SSB signal; then, the carrier and the +1st-order sideband are transmitted with a carrier-to-sideband ratio of 0dB. Theoretical analysis shows that compared to the traditional SSB-modulated optical millimeter-wave signal generation scheme this scheme completely solves the problem of the time shift of code edges caused by dispersion. The simulation results show that the improved SSB modulation scheme has a Q factor of 23.362, the minimum bit error rate is 4.207×10-127 at 73.453km, and the eye diagram is still very clear. Under the premise of meeting the basic requirements of communications, the maximum communications distance can reach 135km, which is 270% of the transmission distance of a traditional SSB modulation model.Thus, the system performance has been greatly improved.

Fiber-terahertz-fiber bridge system in the 355-GHz band using a simple optical frequency comb and a photonics-enabled receiver.

This Letter demonstrates a high-speed fiber-terahertz-fiber system in the 355-GHz band using stable optical frequency comb generation and a photonics-enabled receiver. At the transmitter, a single dual-drive Mach-Zehnder modulator is employed to generate a frequency comb by driving the modulator under an optimal condition. At the antenna site, a photonics-enabled receiver consisting of an optical local oscillator signal generator, a frequency doubler, and an electronic mixer is used to downconvert the terahertz-wave signal to the microwave band. Simple intensity modulation and a direct detection method are used for transmitting the downconverted signal to the receiver over the second fiber link. To demonstrate the proof of concept, we transmitted a 16-quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing signal over a system consisting of two radio-over-fiber links and a 4 m wireless link in the 355-GHz band and achieved a line rate of 60 Gb/s. We also successfully transmitted a 16-QAM subcarrier multiplexing single-carrier signal over the system and achieved a capacity of 50 Gb/s. The proposed system can facilitate the deployment of ultra-dense small cells in high-frequency bands in beyond-5G networks.

Optical Processes behind Plasmonic Applications.

Plasmonics is a revolutionary concept in nanophotonics that combines the properties of both photonics and electronics by confining light energy to a nanometer-scale oscillating field of free electrons, known as a surface plasmon. Generation, processing, routing, and amplification of optical signals at the nanoscale hold promise for optical communications, biophotonics, sensing, chemistry, and medical applications. Surface plasmons manifest themselves as confined oscillations, allowing for optical nanoantennas, ultra-compact optical detectors, state-of-the-art sensors, data storage, and energy harvesting designs. Surface plasmons facilitate both resonant characteristics of nanostructures and guiding and controlling light at the nanoscale. Plasmonics and metamaterials enable the advancement of many photonic designs with unparalleled capabilities, including subwavelength waveguides, optical nanoresonators, super- and hyper-lenses, and light concentrators. Alternative plasmonic materials have been developed to be incorporated in the nanostructures for low losses and controlled optical characteristics along with semiconductor-process compatibility. This review describes optical processes behind a range of plasmonic applications. It pays special attention to the topics of field enhancement and collective effects in nanostructures. The advances in these research topics are expected to transform the domain of nanoscale photonics, optical metamaterials, and their various applications.

Generation of optical UWB signals based on combined bright solitons

We investigate the generation of ultra-wide band (UWB) signal in all optical domain based on combined bright solitons by numerical method. The combined solitons with ultra-wideband characteristics can be obtained by multiple bright solitons. The power spectrum can be modulated by pulse interval, pulse width and phase difference of combined bright solitons to satisfy with the Federal Communications Commission (FCC) spectrum mask. Meanwhile, the transmissions of combined bright solitons in single-mode fibers are discussed. The fiber loss and dispersion effects have the influence on the transmissions of combined bright solitons. In order to eliminate dispersion effects, the stable transmission of signals in dispersion decreasing fibers is proposed.

Nonlinear Optical Signal Generation Mediated by a Plasmonic Azimuthally Chirped Grating

Plasmonic gratings are simple and effective platforms for nonlinear signal generation since they provide a well-defined momentum for photon-plasmon coupling and local hot spots for frequency conversion. Here, a plasmonic azimuthally chirped grating (ACG), which provides spatially resolved broadband momentum for photon-plasmon coupling, was exploited to investigate the plasmonic enhancement effect in two nonlinear optical processes, namely two-photon photoluminescence (TPPL) and second harmonic generation (SHG). The spatial distributions of the nonlinear signals were determined experimentally by hyperspectral mapping with ultrashort pulsed excitation. The experimental spatial distributions of nonlinear signals agree very well with the analytical prediction based on photon-plasmon coupling with the momentum of the ACG, revealing the "antenna" function of the grating in plasmonic nonlinear signal generation. This work highlights the importance of the antenna effect of the gratings for nonlinear signal generation and provides insight into the enhancement mechanism of plasmonic gratings in addition to local hot spot engineering.

Evaluation and analysis of optically injection-locked semiconductor laser characteristics for optical complex signal generation

In this paper, we present an investigation of the optical injection-locked parameters which utilize an approach to creating optical complex signals using optically injection-locked (OIL) semiconductor lasers. Subsequently, we discuss the impact of the OIL parameters on the locking map, manufacturing the corresponding complex signal area, pole-zero diagram, and frequency response of the system. The steady-state analysis of the rate equations indicates that changing OIL parameters can result in simultaneous optical AM and PM of the OIL laser while preserving the injection locking state. Based on the simulation results, we found that using strong R inj and high negative Δfinj (which are mandatory for generating high-quality complex modulation) along with α = 3; can improve the performance in producing complex signal area as well as the frequency response, while using other settings does not lead to the development of both. Therefore, we achieve the maximum generated complex signal area and the -3dB frequency by using an adjusted parameter value for the system, which results in a faster modulation speed and higher quality of the optical complex modulation.

Transmission of 120 Gbaud QAM With an All-Silicon Segmented Modulator

Segmenting a silicon modulator can substantially increase its electro-optic bandwidth without sacrificing modulation efficiency. We demonstrate a segmented silicon IQ modulator and experimentally explore both modulator design and operating point to optimize systems trade-offs in coherent detection. An electro-optic bandwidth of greater than 40 GHz is measured for a 4-mm-long segment, and greater than 60 GHz for a 2-mm-long segment. We evaluate optical transmission experimentally at 120 Gbaud for 16-ary quadrature amplitude modulation (QAM) and 32QAM. The segments are operated in tandem with identical data at each segment. We present an experimental method to align data timing between the segments. Through the optimization of segment biasing and linear compensation, we have achieved a bit error rate (BER) of 16QAM well below the 20% forward error correction (FEC) threshold ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2\times 10^{-2}$</tex-math></inline-formula> ). Adding nonlinear pre-compensation allows for 32QAM with a BER below the 24% FEC threshold ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$4.5\times 10^{-2}$</tex-math></inline-formula> ), enabling a net rate of 483 Gbs per polarization. The modulator can also be operated as an optical digital analogy converter for complex optical signal generation, for which 100 Gbs is achieved for a proof of concept.

Effect of High Frequency Gain on the Performance of Optical Costas Loop in Face of Loop Delay

Objectives: Optical costas loops (OCLs) are widely used in optical communication as homodyne receivers. Due to use of different electronic counterparts and fibre optic cable inherent loop delay always presents in the system. The steady state behaviours of optical costas loop are highly affected by the presence of loop delay. Different nonlinear behaviours may be observed due to presence of delay. There are two main objectives of this article. Firstly, how OCL can be operated as stable receiver up to some large value of loop delay by using a proportional plus integrating type loop filter (LF). Secondly, how a controlled chaotic optical signal can be generated from OCL by choosing the system parameters in correct manner. Methods: To investigate system behaviours of OCL both analytical and numerical methods have been used. Stability analysis of OCL has been done by Routh-Hurwitz method. From stability analysis, it is possible to predict the stable and unstable behaviour of the OCL in presence of delay and how system stability can be improved by high frequency gain value of LF. Numerical methods have also been used to solve the nonlinear equation of OCL to observe real time behaviours. Findings: Analytical findings show that loop stability can be improved by increasing the value of high frequency gain of LF. For large value of loop delay, chaotic oscillation of phase error may be observed in OCL. The chaotic oscillation can also be controlled by high frequency gain with certain extent value of loop delay. All the numerical findings have been properly verified with numerical results. Novelty: This article describes how effects of loop delay can be controlled to run OCL in steady as well as in unsteady state. From designer’s point of view this study would be helpful to choose correct values of system parameters to improve the performance of OCL in optical communication. It also gives the idea for generation of chaotic optical signal, which is used in secured communications. Keywords: Optical Costas loop; Optical Phase locked loop Phase detector; Loop filter; Nonlinear dynamics; and optical communications

A Novel System for Quasi-Continuous THz Signal Transmission and Reception.

This paper presents a novel system for generating and receiving quasi-continuous (QC) TeraHertz (THz) waves. A system design and theoretical foundation for QC-THz signal generation are presented. The proposed QC-THz system consists of commercially available photo-conductive antennas used for transmission and reception of THz waves and a custom-designed QC optical signal generator, which is based on a fast optical frequency sweep of a single telecom distributed-feedback laser diode and unbalanced optical fiber Michelson interferometer used for a high-frequency modulation. The theoretical model for the proposed system is presented and experimentally evaluated. The experimental results were compared to the state-of-the-art continuous-wave THz system. The comparison between the continuous-wave THz system and the proposed QC-THz system showed the ability to transmit and receive QC-THz waves up to 300 GHz. The upper-frequency limit is bounded by the length of the used Michelson interferometer. The presented design of THz signal generation has a potential for industrial application because it is cost-efficient and can be built using commercially available components.

Wavelength-Tunable Optical Two-Tone Signals Generated Using Single Mach-Zehnder Optical Modulator in Single Polarization-Mode Sagnac Interferometer

We demonstrate 60 GHz separation optical two-tone signal generation at arbitrary C-band wavelengths without involving complicated optical wavelength filtering. By utilizing a polarizer, the selective suppression of undesired low-order optical sidebands has been proven and optimized based on model analysis. By utilizing this scheme in conjunction with the optimized parameters, more than 20 dB of suppression of undesired optical sidebands have been successfully achieved over a 40 nm wavelength range. This scheme allows us to generate optical two-tone signals at the desired wavelength.

A Filterless Generation of Optical Millimeter Wave Signal Based on Frequency 16-Tupling Using Cascaded Polarization Modulators

Millimeter wave (MMW) frequencies are becoming vital as they bolster a large number of applications requiring higher data rates. In this paper, we have demonstrated a frequency multiplication technique based on external modulation for a 160 GHz MMW signal generation. The proposed scheme which uses a four-stage cascaded structure of polarization modulators proves to be a lucrative solution since the selected modulation index of 2.826 is phenomenally low. A precise choice of phase shifts between the cascaded stages ensures two eighth-order peaks spaced 160 GHz apart. This technique renders Radio Frequency Spurious Suppression Ratio and Optical Sideband Suppression Ratio of 45 and 65 dB, respectively. Simulation results are verified from a mathematical standpoint. The requirement of a Radio Frequency Local Oscillator with a higher frequency has been eliminated by a higher value of frequency multiplication factor.

SNR Enhancement of up to 9.5 Db Utilizing Four-Wave Mixing for Angle-Modulated Analog Optical Links

Angle modulation, such as phase and frequency modulation (FM/PM), has recently attracted attention for improving the fidelity of analog optical links. This is because angle modulation can enhance the signal-to-noise ratio (SNR) of the original analog message simply by increasing the modulation index or the bandwidth. However, direct generation of a broadband optical angle-modulated signal is not necessarily easy. On the other hand, there is an indirect generation method, where a narrowband angle-modulated signal is first generated and then converted to a broadband signal with the help of nonlinear devices. This method is often used in FM radio systems, but few reports are available on the optical implementation of this indirect method. In this paper, therefore, we propose the optical implementation by using four-wave mixing (FWM) in an optical fiber. Since an optical fiber naturally has a third-order nonlinearity (i.e., the Kerr effect), it should be possible to use fiber nonlinearity for the optical implementation of the indirect method to increase the bandwidth of an optical angle-modulated signal. We propose two types of FWM-based methods. In the first type, an angle-modulated signal is injected into a dispersion-shifted fiber (DSF) with an unmodulated pump wave. Consequently, one of the idlers generated via the FWM has a double modulation index, and the SNR of the original signal can be enhanced by 6 dB. In the second type, the input becomes a conjugate pair of an angle-modulated signal. Consequently, the idler has a threefold modulation index, and therefore, this type enhances the SNR by 9.5 dB. We experimentally confirmed the concept. The results showed that the modulation index can actually be increased almost threefold, and the idler can enhance the SNR of the original signal by approximately 8.8 dB.

A March to Shape Optical Artificial Olfactory System toward Ultrasensitive Detection of Improvised Explosives

Improvised explosives (IEs) have been frequently used in explosion‐based terrorist attacks, and have aroused widespread concerns from governments to academic societies. Due to the fact that IEs mostly exist as solids, there is a pressing demand for sensors to adapt to acquire the information from the solid state. Chemical sensors usually comprise with probes designed based on the chemical properties of the analytes, and generate signals through specific chemical interactions, which would not be affected by the state of the target substance. Colorimetry and fluorescence, known for their intuitionistic (recognizable by human eyes), portable (independent of large‐scale analytical equipment), highly specific, sensitive, and environmental interference‐free characteristics, are commonly adopted optical chemical detection methods in materials analysis and environmental monitoring. Based on this, the exploration of optical artificial olfactory system, which mimics the working principle of natural olfactory system and acquires sensing signal by optical methods, has emerged to be a promising tool for IEs detection. Here, the basic working principle and the necessary components of optical artificial olfactory system are recommended, including probe molecule, array composition, pattern recognition and device construction. The potential development direction employing molecular recognition of IEs, generation, and acquisition methodology of optical signals are also prospected.