Electronic Bottleneck Research Articles

High-Precision Photonics-Assisted Two-Step Microwave Frequency Measurement Combining Time and Power Mapping Method.

Photonics-assisted methods for microwave frequency measurement (MFM) show great potential for overcoming electronic bottlenecks and offer promising applications in radar and communication due to their wide bandwidth and immunity to electromagnetic interference. In common photonics-assisted MFM methods, the frequency-to-time mapping (FTTM) method has the capability to measure various types of signals, but with a trade-off between measurement error, measurement range, and real-time performance, while the frequency-to-power mapping (FTPM) method offers low measurement error but faces great difficulty in measuring signal types other than single-tone signals. In this paper, a two-step high-precision MFM method based on the combination of FTTM and FTPM is proposed, which balances real-time performance with measurement precision and resolution compared with other similar works based on the FTTM method. By utilizing high-speed optical sweeping and an optical filter based on stimulated Brillouin scattering (SBS), FTTM is accomplished, enabling the rough identification of multiple different signals. Next, based on the results from the previous step, more precise measurement results can be calculated from several additional sampling points according to the FTPM principle. The demonstration system can perform optical sweeping at a speed of 20 GHz/μs in the measurement range of 1-18 GHz, with a measurement error of less than 10 MHz and a frequency resolution of 40 MHz.

Three-Soliton Interactions and the Implementation of Their All-Optical Switching Function

As a key component in all-optical networks, all-optical switches play a role in constructing all-optical switching. Due to the absence of photoelectric conversion, all-optical networks can overcome the constraints of electronic bottlenecks, thereby improving communication speed and expanding their communication bandwidth. We study all-optical switches based on the interactions among three optical solitons. By analytically solving the coupled nonlinear Schrödinger equation, we obtain the three-soliton solution to the equation. We discuss the nonlinear dynamic characteristics of various optical solitons under different initial conditions. Meanwhile, we analyze the influence of relevant physical parameters on the realization of all-optical switching function during the process of three-soliton interactions. The relevant conclusions will be beneficial for expanding network bandwidth and reducing power consumption to meet the growing demand for bandwidth and traffic.

Microwave photonics frequency measurement with improved accuracy based on an artificial neural network.

Photonics-assisted techniques for microwave frequency measurement (MFM) show great potential for overcoming electronic bottlenecks, with wild applications in radar and communication. The MFM system based on the stimulated Brillouin scattering (SBS) effect can measure the frequency of multiple high-frequency and wide-band signals. However, the accuracy of the MFM system in multi-tone frequency measurement is constrained by the SBS bandwidth and the nonlinearity of the system. To resolve this problem, a method based on an artificial neural network (ANN) is suggested, which can establish a nonlinear mapping between the measured two-tone signal spectra and the theoretical frequencies. Through simulation verification, the ANN optimized frequencies within the range of (0.5, 27) GHz of the MFM system show 79%, 76%, 70%, 44% reduction in errors separately under four spectral signal-to-noise ratios (SNR) conditions, 20dB, 15dB, 10dB, 0dB, and the frequency resolution is improved from 30MHz to 10MHz.

Compact hybrid silicon nitride and lithium niobate nano-film photoelectronic reversible logic gate

Photoelectronic hybrid logic operation improves digit circuit efficiency without any additional photoelectric conversion, especially a photoelectronic reversible logic gate may reduce energy dissipation. In this paper, a compact photoelectronic reversible logic gate is proposed based on a hybrid silicon nitride and lithium niobate nano-film waveguide. Tow Mach-Zehnder modulators are cascaded together to construct the main part of the compact photoelectronic reversible logic gate. The whole length of the gate is only 4.4mm, one hundredth of the length of the common proton exchange lithium niobate modulator. By operating at the wavelength of 1.55μm, the proposed Mach-Zehnder modulator only requires 4.9V voltage to complete a full cross-coupling, which is well compatible with CMOS technology. It is demonstrated that at the wavelength range of 1.4μm to 1.6μm, the average insertion loss is 0.6dB, the minimum crosstalk is -47dB, and the maximum extinction ratio is 41dB; in the voltage range of 4V to 6V, the average insertion loss is 0.63dB, the minimum crosstalk is -26dB, and the maximum extinction ratio is 22dB. These features indicate that the photoelectronic reversible logic gates have good performances, bringing the photoelectronic logic gates into a new design parameter space and providing a possible solution for easing the electronic bottleneck.

Slot-Waveguide Based All-Optical RF Spectrum Analyzer

All-optical radio-frequency spectrum analyzers (AORFSAs) with ultrabroad bandwidth break the electronic bottleneck and provide an efficient frequency analysis means for ultrafast optical signals in communications, signal generation and processing systems. Here, we propose and experimentally demonstrate an AORFSA built on the cross-phase modulation effect in a 50 cm long CMOS-compatible photonic slot-waveguide. The waveguide has a 100 nm thick thin-film core of fused silica that is sandwiched by two 750 nm thick cladding layers of high-index doped silica, which shows optimized dispersion and comparable nonlinear characteristics. The measured 3 dB bandwidth of the proposed slot-waveguide-based AORFSA has a three-fold increase over the conventional channel waveguide having the same dimension and length. The sensitivity and wavelength- and polarization-dependence properties are investigated, confirming the proposed waveguide as a versatile platform for frequency analysis of ultrafast optical signals, such as Kerr microcombs with hundreds of GHz or even THz mode spacing.

Gain optimization and data modeling of S-band of Tm-doped fiber amplifier based on genetic algorithm

At present, fiber amplifiers are indispensable in the field of communication, Erbium-doped fiber amplifiers (EDFA) are currently more mature fiber amplifiers, but because of electronic bottlenecks, they have approached saturation in recent years. Thus, the study and application of fiber amplifiers doped with other rare earth elements has become a new goal at present. At the same time, expanding the available bandwidth of the fiber amplifier to a higher or lower direction has also become a major task. This article discusses the gain of thulium-doped fiber amplifiers at 1400 nm – 1450 nm (S-band) and uses the genetic algorithm to optimize the fiber length and doping concentration to find the optimal solution, this article also analyzes the change in gain at different fiber lengths and doping concentrations. The results show that the fiber length is 56.2705 meters, and the doping concentration is 59.9502 ×1024 per square meter, at which the gain reaches the peak is 65.19. The results show that the thulium-doped fiber amplifier (TDFA) in this band has good amplification characteristics, and it can be meticulously studied based on this method in the future to obtain more accurate results. It can also be solved using other algorithms, such as Quantum Genetic Algorithms.

TiN/Ti3C2 Heterojunction Microfiber-Enhanced Four-Wave Mixing-Based All-Optical Wavelength Converter

As a novel nanomaterial, the TiN/Ti3C2 heterojunction has been demonstrated to possess exceptional optoelectronic properties, offering significant potential for applications in fields such as communication, optical sensors, and image processing. The rapid evolution of the internet demands higher communication capacity and information processing speed. In this context, all-optical wavelength conversion, a pivotal technique in all-optical signal processing, holds paramount importance in overcoming electronic bottlenecks, enhancing wavelength utilization, resolving wavelength competition, and mitigating network congestion. Utilizing the idle light generated through the four-wave mixing (FWM) process accurately mimics the bit patterns of signal channels. This process is inherently rapid and theoretically capable of surpassing electronic bottlenecks with ease. By placing an optical filter at the fiber output end to allow idle light passage while blocking pump and signal light, the output becomes a wavelength-converted replica of the original bitstream. It has been verified that TiN/Ti3C2 heterojunction-coated microfiber (THM) exhibits outstanding third-order nonlinear coefficients. Building upon this, we achieved a THM-enhanced FWM all-optical wavelength converter, resulting in a ~4.48 dB improvement in conversion efficiency. Compared to conventional high-nonlinear fibers, this compact device significantly reduces fiber length and can be easily integrated into current high-speed optical communication networks. It demonstrates broad prospects in the realms of all-optical signal processing, robotic applications, ultra-high-speed communication, and beyond.

Review of 2 × 2 Silicon Photonic Switches

With the advent of 5G, artificial intelligence (AI), Internet of Things (IoT), cloud computing, Internet plus, and so on, data traffic is exploding and higher requirements are put forward for information transmission and switching. Traditional switching requires optical/electrical/optical conversions, which brings additional power consumption and requires the deployment of large amounts of cooling equipment. This increases the cost and complexity of the system. Moreover, limited by the electronic bottleneck, electrical switching will suffer from many problems such as bandwidth, delay, crosstalk, and so on, with the continuous reduction in device footprint. Optical switching does not require optical/electrical/optical conversions and has lower power consumption, larger capacity, and lower cost. Silicon photonic switches received much attention because of their compatibility with the complementary metal-oxide-semiconductor (CMOS) process and are anticipated to be potential candidates to replace electrical switches in many applications such as data center and telecommunication networks. 2 × 2 silicon photonic switches are the basic components to build the large-scale optical switching matrices. Thus, this review article mainly focuses on the principle and state of the art of 2 × 2 silicon photonic switches, including electro-optic switches, thermo-optic switches, and nonvolatile silicon photonic switches assisted by phase-change materials.

Self-synchronized temporal-spectral characterization system for revealing ultrafast fiber laser dynamics

Due to the electronic bottleneck limited real-time measurement speed of common temporal-spectral detection and the particle-like nature of optical soliton enabled nonrepeatable transient behaviors, capturing the ultrafast laser pulses with unknown times of arrival and synchronously characterizing their temporal-spectral dynamic evolution is still a challenge. Here, using the Raman soliton frequency shift based temporal magnifier and dispersive Fourier transform based spectral analyzer, we demonstrate a self-synchronized, ultrafast temporal-spectral characterization system with a resolution of 160 fs and 0.05 nm, and a recording length above milliseconds. The synchronized nonlinear process makes it possible to image full-filled temporal sub-picosecond pulse trains regardless of their arrival times and without extra pump lasers and photoelectric conversion devices. To demonstrate the significance of this improvement, a buildup dynamic process of a soliton laser with a complex breakup and collisions of multisolitons is visually displayed in the spectral and temporal domains. The soliton dynamic evolution processes observed by our characterization system are in one-to-one correspondence with the numerical simulation results. We believe this work provides a new multidimensional technique to break the electronic bottleneck to gain additional insight into the dynamics of ultrafast lasers and nonlinear science.

Broadband Microwave Photonic Channelizer with 18 Channels Based on Acousto-Optic Frequency Shifter

A microwave photonic channelizer can achieve instantaneous reception of ultra-wideband signals and effectively avoid electronic bottleneck; therefore, it can be perfectly applied to a wideband radar system and electronic warfare. In channelization schemes based on an optical frequency comb (OFC), the number of comb lines usually depends on that of the sub-channels. In order to improve the utilization rate of the comb lines of OFC, we propose a scheme to shift the frequency of OFC by using an acousto-optic frequency shifter (AOFS), which can obtain three times the number of sub-channels of the comb lines of an OFC. In order to simplify the experiment, only a three-line OFC is used in the experiment. A three-line local oscillator (LO) OFC is frequency-shifted up and down by two AOFSs, and nine optical LO signals with different frequencies are obtained, thereby realizing the simultaneous reception of eighteen sub-channels. The proposed scheme enjoys a large number of sub-channels and minimal channel crosstalk. Experimental results demonstrate that a 9-GHz bandwidth RF signal covering 10–19 GHz is divided into 18 sub-channels with a sub-bandwidth of 500 MHz. The image rejection ratio of the sub-channels is about 23 dB, and the spurious-free dynamic range (SFDR) of the receiver can reach 98 dB·Hz2/3.

A Microwave Photonic Channelized Receiver With Self-Interference Cancellation

Microwave photonic channelized receiver can break through the electronic bottleneck, improve the throughput of satellite payload, and is expected to be widely used in broadband satellite communications. To solve the self-interference problem in the full-duplex satellite relay system, a microwave photonic channelized receiver with a self-interference cancellation (SIC) function is proposed in this paper. The equal interval division of broadband radio frequency (RF) signals is realized through polarization multiplexing technology and optical frequency shifting technology. In addition, by constructing a reference interference signal and matching the delay and amplitude in the optical domain, the self-interference signal is eliminated to avoid the receiver blockage caused by interference leakage. Theoretical derivation and experiment research are carried out, and a wideband signal with 3-GHz bandwidth is down-converted to six sub-channels with a frequency range of 0.5 GHz–1 GHz. Under the single-tone test, the isolation between sub-channels exceeds 31 dB, and the SIC depth exceeds 40 dB. When the sub-channels carry the 16quadrature amplitude modulation (QAM) signals with the bandwidth of 50 MHz, the SIC depth over 26 dB is achieved, and the error vector magnitude (EVM) is 7.6%. Under the two-tone test, the SFDR of the sub-channel is 93.5 dB.Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> .

Research and Simulation of OCDM Switch Layer Based on 2D WDM-Optical Code Switching Structure

Optical Communication is widely used in military and civilian backbone network communication, but due to the limitation of “electronic bottleneck”, the ability of network nodes to process information and optical layer data transmission capacity is seriously mismatched, which directly causes optical cross connectors in optical nodes. The number of ports carried has skyrocketed. In order to improve the processing speed of network nodes, this paper studies the four-layer multi-granularity switching system of optical fiber, wavelength band, wavelength, and optical code, and finally builds a complete OCDMA system through simulation software, simulates multi-user simulation, and successfully realizes The encoding and decoding process is analyzed, and the performance simulation and analysis of the core switching module of the four-layer multi-layer optical switching system-OCDM switching module are carried out, and the feasibility and superiority of the selected system are verified.

Microwave photonic multiform microwave frequency shift keying signal generator.

A photonic approach to realizing multiform microwave frequency shift keying (FSK) signal generation is proposed and demonstrated. In the scheme, a commercial dual-polarization quadrature phase shift keying modulator (DP-QPSKM) is employed to generate two orthogonally-polarized signals containing specific optical sidebands, and a subsequent Sagnac loop structure govern the interference results of these two signals. From a theoretical analysis, when the modulators are properly biased, microwave FSK signal with fixed double relationship or flexibly tunable subcarrier frequencies can be obtained, and high frequency multiplication can be realized in the meantime. Furthermore, a photonic-optimized coherent demodulation structure is designed to recover the binary coding data, which can effectively avoid the electronic bottleneck. Simulation has been performed to investigate the mechanism and the discussions about the robustness to non-ideal parameters including DC bias, phase shift and polarization angle are also given. In the proof-of-concept experiment, microwave FSK signal with subcarrier frequencies of 2/4, 2.2/3.8, 2.4/3.6, 2.6/3.4, 2.8/3.2 GHz are generated, and the correct binary coding data is successfully recovered with the aid of simulation platform. The simulation and experimental results can verify the feasibility of the proposed multiform microwave FSK signal generator, which may find applications in modern radar and communication systems.

Ultrafast and real-time physical random bit extraction with all-optical quantization

Optical chaos generated by perturbing semiconductor lasers has been viewed, over recent decades, as an excellent entropy source for fast physical random bit generation (RBG) owing to its high bandwidth and large random fluctuations. However, most optical-chaos-based random bit generators perform their quantization process in the electrical domain using electrical analog-to-digital converters, so their real-time rates in a single channel are severely limited at the level of Gb/s due to the electronic bottleneck. Here, we propose and experimentally demonstrate an all-optical method for RBG where chaotic pulses are quantized into a physical random bit stream in the all-optical domain by means of a length of highly nonlinear fiber. In our proof-of-concept experiment, a 10-Gb/s random bit stream is successfully generated on-line using our method. Note that the single-channel real-time rate is limited only by the chaos bandwidth. Considering that the Kerr nonlinearity of silica fiber with an ultrafast response of few femtoseconds is exploited for composing the key part of quantizing laser chaos, this scheme thus may operate potentially at much higher real-time rates than 100 Gb/s provided that a chaotic entropy source of sufficient bandwidth is available.

High-performance linear frequency-modulated signal generation based on optically injected semiconductor laser with dual-loop optoelectronic feedback

&lt;sec&gt;Linear frequency-modulated (LFM) waveforms have numerous applications in high-resolution radar detection, high-speed wireless communication, and high precision measurement. The generation of LFM microwave signals based on conventional electronic technologies is limited in their center frequency and bandwidth, which are usually less than a few gigahertz. Fortunately, the inherently large bandwidth offered by photonic technology is very hopeful of breaking through the electronic bottleneck. A variety of photonics-based approaches to generating the LFM waveforms have been reported, including the frequency-to-time mapping method and the external modulation method. However, these solutions suffer poor tunability or expensive RF sources. In recent years, the LFM waveform generation based on optically injected semiconductor lasers (OISLs) has attracted increasing attention. By introducing a low-speed electrical signal to control the period-one (P1) dynamics of an OISL, the LFM waveforms with a large bandwidth are generated. Nonetheless, the generated microwave signal has poor spectral purity, which restricts its many practical applications.&lt;/sec&gt;&lt;sec&gt;In this work, a high-performance microwave LFM waveform generation scheme based on an OISL with dual-loop optoelectronic feedback is proposed and demonstrated experimentally. In this scheme, the optical injection strength of an OISL is controlled first by a triangular-like voltage signal to generate LFM waveforms with a large bandwidth. Then, the quality of the generated LFM signal is comprehensively improved by introducing a delay-matched dual-loop optoelectronic feedback structure. Based on the Fourier domain mode locking principle (FDML) and the self-injection locking technique, both a short-delay optoelectronic feedback loop and a long-delay optoelectronic feedback loop are introduced to simultaneously improve the spectral purity and phase stability of the generated LFM signals. In the proof-of-concept experiment, by analyzing the spectral quality and phase deviation of the generated LFM signal, a comb contrast of 40 dB, a comb linewidth of 1 kHz, and a phase deviation ∆&lt;i&gt;φ&lt;/i&gt; of less than π/3 are simultaneously obtained. In addition, the parameters such as bandwidth and center frequency of the generated LFM signal generated can be flexibly tuned, and an LFM signal with a large bandwidth up to 8 GHz (18–26 GHz) is generated in the experiment. The proposed scheme features a simple and compact structure, high spectral quality and flexible tuning, thus may find applications in broadband radar and high-speed communication systems.&lt;/sec&gt;

Microwave Photonic Channelizer With Large Instantaneous Bandwidth Based on AOFS

The microwave photonic channelizer can convert the RF signal into the optical domain for transmission and procession, effectively avoiding the limitation of electronic bottleneck, and realizing the instantaneous reception of ultra-wideband signal or multi-frequency signals, which can be perfectly applied to radar system and electronic warfare. In this paper, a microwave photonic channelizer based on dual-output image-reject mixer is proposed, both the signal path and the local oscillator path are divided into three paths by using an optical coupler. An acousto-optic frequency shifter (AOFS) is used by the optical local oscillator to shift the frequency to the left and right and then enters the image rejection mixer with the signal path. Finally, a 6 GHz bandwidth RF signal is divided into six subchannels with a bandwidth of 1 GHz to achieve simultaneous reception. This scheme needs no optical frequency comb and doubles the channelization efficiency, the image rejection ratio of the sub-channels is about 22 dB, and the spurious-free dynamic range of the system can reach 103.2 dB·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> .

All-Optical Graphene Oxide Modulator Based on Phase-Shifted FBG

An all-optical graphene oxide modulator based on phase-shifted FBG is proposed and experimentally proved to overcome the electronic bottleneck. The phase-shifted FBG is formed by tapering and the surface of nanofiber is covered with graphene oxide film to adjust the phase-shift. In order to reduce the complexity of production and improve the practicability, graphene oxide aqueous solution is used to produce the film on the surface of nanofiber. Experimental results show that the graphene oxide can obtain different phase shifts in phase-shifted FBG by changing the pump intensity. The extinction ratio of the proposed modulator can reach up to 1.1 dB. Besides, the experimental result of transmission spectrum is consistent with the simulated result. With its narrow band-stop characteristics, multiple modulators can be cascaded to achieve the wavelength division, which takes full advantage of low-loss. Due to the ultra-fast and broadband response of graphene, the theoretical rate of the modulator can reach 200 GHz. Therefore, the modulator has broad applications in ultra-high-speed all-optical networks.

Biased Balance Detection for Fiber Optical Frequency Comb Based Linear Optical Sampling

Linear optical sampling (LOS) is a powerful technique to circumvent the electronic bottleneck arising in optical modulation analyzer (OMA). To extend the range of operation wavelength for the LOS-based OMA, the fiber optical frequency comb (FOFC) is proposed to replace the narrowband mode-locked fiber laser (NMFL) as an optical sampling source. However, this procedure reduces the signal-to-noise ratio (SNR), due to the constraints of the unideal response of balanced photodetector (BPD) and the limited power per FOFC tone. Here, we investigate the biased balance detection (BBD) scheme to overcome such issue. Our simulation results show that, the characterization performance of the FOFC-based LOS with the help of the BBD scheme is almost the same as that of the NMFL-based LOS, when the PDM-QPSK/16QAM/64QAM signals are set as the signal under test (SUT). Meanwhile, we find that the dynamic range of SUT input power is determined by the BPD imbalance and the FOFC power. By increasing either the average power of the FOFC from 4 to 10 mW or the imbalance of the BPD from 1.03 to 1.04, we can enhance the dynamic range of SUT input power by 8.8 mW and 6.6 mW, respectively. Finally, we develop the equipment and experimentally verify the BBD scheme by a precise characterization of 32 GBaud PDM-QPSK signal.

Optical domain despreading method of optical time-domain reflectometer using spread spectrum technology

The advantages of optical time-domain reflectometer (OTDR) using spread spectrum technology are analyzed briefly. For the shortcomings of spread spectrum OTDR in traditional despreading method, the concept of optical domain multiplier is first proposed, i.e., the most important multiplication operation in despreading is realized by modulating the phase of Mach–Zehnder modulator before photoelectric conversion. The proposed two methods of despreading in optical domain overcome the electronic bottleneck of correlative despreading in electrical domain, and solve the various restrictions on the application of high-speed spreading code in OTDR. Simulations verify the correctness and feasibility of the two methods.

RF Self-Interference Cancellation for Radio-Over-Fiber Link Based on Dual Phase Modulation in Sagnac Loop

The in-band full-duplex (IBFD) systems can send and receive data simultaneously in the same frequency band. Although the electromagnetic interference among RF channels can be released using radio over fiber (RoF) links, the receiving antenna is susceptible to the signal leakage from adjacent transmitting antennas. Due to the electronic bottlenecks, traditional RF self-interference cancellation (SIC) systems have some problems, such as low operating frequency, narrow transmission bandwidth, and electromagnetic interference, which seriously reduces the communication performance. In this paper, a photonic RF SIC system based on dual-phase modulation in a Sagnac loop is proposed to further increase the resistance to electromagnetic interference of the IBFD systems. Based on the principle of polarization multiplexing, the damaged received signal and local interference signal are modulated on two beams of a light wave with orthogonal polarization states. The received interference signal can be canceled by polarization adjustment. In the experiment, a single- frequency interference cancelation depth of 45 dB is achieved in the proposed photonic SIC system over the operating frequency range of 5-20 GHz. Also, a demonstration of cancellation for modulated interference with a center frequency of 10 GHz and bandwidths of 20, 30, and 50 MHz is carried out.