Electrical Filter Research Articles

Opto-Mechanical Interactions in Multi-Core Optical Fibers and Their Applications

Optical fibers containing multiple cores are being developed towards capacity enhancement in space-division multiplexed optical communication networks. In many cases, the fibers are designed for negligible direct coupling of optical power among the cores. The cores remain, however, embedded in a single, mechanically-unified cladding. Elastic (or acoustic) modes supported by the fiber cladding geometry are in overlap with multiple cores. Acoustic waves may be stimulated by light in any core through electrostriction. Once excited, the acoustic waves may induce photo-elastic perturbations to optical waves in other cores as well. Such opto-mechanical coupling gives rise to inter-core cross-phase modulation effects, even when direct optical crosstalk is very weak. The cross-phase modulation spectrum reaches hundreds of megahertz frequencies. It may consist of discrete and narrow peaks, or may become quasi-continuous, depending on the geometric layout. The magnitude of the effect at the resonance frequencies is comparable with that of intra-core cross-phase modulation due to Kerr nonlinearity. Two potential applications are demonstrated: single-frequency opto-electronic oscillators that do not require radio-frequency electrical filters, and point-sensing of liquids outside the cladding of multi-core fibers, where light cannot reach.

Fine Tunable PT-Symmetric Optoelectronic Oscillator Based on Laser Wavelength Tuning

A fine tunable parity-time symmetric optoelectronic oscillator (PT-OEO) based on laser wavelength tuning is proposed and experimentally demonstrated. In the PT-OEO, an intensity modulator (IM) and a dispersion compensating fiber (DCF) are merged into the loop. Tuning the laser wavelength leads to a reconfigurable dispersion-induced power fading, serving as rough tunable oscillation mode selection. Meanwhile, to implement a fine-mode selection, parity-time symmetry breaking is introduced. Consequently, a fine tunable PT-OEO is achieved without using a high quality-factor (Q-factor) electrical filter. Experiment shows that the frequency of the generated signal can be tuned from 20.34 to 19.49 GHz with a step of 203 MHz, when the laser wavelength is manipulated from 1545 to 1565 nm. The phase noise is evaluated as −116.1 dBc/Hz @ 10-kHz offset frequency.

Signal Processing Criteria Based on Electro-Optic Filters for Fiber Optic Access Transceiver Systems

Abstract The study outlines the different types of electro-optic filters that are used in fiber optic access transceiver systems. These filters are classified into the electrical filter in the receiver side and optical filters are located between fiber optic and transmitter. The optical filters are, namely, Fabry Perot, Gaussian, and Bessel filters. While electrical filters that are namely low pass Bessel, low pass Gaussian, and low pass squared raised cosine roll-off filters. The study emphasizes the important criteria in the employment of electro-optic filters in this system for signal fast processing. The Fabry Perot optical filters in addition to low pass squared raised cosine roll-off filters are clarified the best-obtained results in the comparison with other proposed filters.

Photonic generation of frequency-doubled microwave waveform based on a PDM-MZM modulator

A novel and simple photonic approach for frequency-doubled microwave waveforms generation based on a polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is proposed and experimentally demonstrated. The PDM-MZM is driven by a local oscillation (LO) signal through a 90 degree hybrid coupler. One sub-modulator of the PDM-MZM is biased at the peak transmission point and the other sub-modulator is biased at the null transmission point. The optical signals from the two arms are polarization multiplexed at the output of the PDM-MZM and then injected into a photodetector (PD) for photoelectrical conversion. By properly controlling the amplitudes of the LO signal, the triangular and square waveforms with a repetition rate twice the frequency of the LO signal can be generated. This scheme has features of compact, low-cost structure and simple operation. Simultaneously, the frequency of the generated waveform can be tuned over a wide bandwidth since there is no optical or electrical filter involved.

Microwave multi-frequency measurement based on an optical frequency comb and a photonic channelized receiver.

A new method, to the best of our knowledge, to measure frequencies of received microwave signal based on an optical frequency comb (OFC) and a photonic multi-channel receiver is proposed and simulated. The measurement system mainly includes a seed laser, an OFC generator composed of two cascaded Mach-Zehnder modulators, a frequency shifter, an intensity modulator, a wavelength-division demultiplexer, photodiodes (PDs), and electrical filters. Two sets of beat signals need to be obtained in the measurement process. By analyzing the two sets of beat signals, multiple frequency components of the microwave signal can be measured at a time. The validity of the proposed scheme is verified by VPI simulation software. It is shown that microwave frequencies within dozens of gigahertz can be precisely measured, and factors affecting the frequency measurement range are also studied.

A Monolithically Integrated Laser-Photodetector Chip for On-Chip Photonic and Microwave Signal Generation

An Indium-phosphide-based monolithically integrated photonic chip comprising of an amplified feedback laser (AFL) and a photodetector was designed and fabricated for on-chip photonic and microwave generation. Various waveforms including single tone, multi-tone, and chaotic signal generation were demonstrated by simply adjusting the injection currents applied to the controlling electrodes. The evolution dynamics of the photonic chip was characterized. Photonic microwave with frequency separation tunable from 26.3 GHz to 34 GHz, chaotic signal with standard bandwidth of 12 GHz were obtained. An optoelectronic oscillator (OEO) based on the integrated photonic chip was demonstrated without using any external electrical filter and photodetector. Tunable microwave outputs ranging from 25.5 to 26.4 GHz with single sideband (SSB) phase noise less than −90 dBc/Hz at a 10-kHz offset from the carrier frequency were realized.

Photonic generation of frequency-doubled triangular waveforms based on a dual parallel Mach–Zehnder modulator

We propose a photonic approach to generating frequency-doubled triangular waveforms using a dual-parallel Mach–Zehnder modulator (DPMZM). Most previous modulator-based schemes require additional processing of optical sidebands using filters or a dispersive element. In our work, optical processing of optical components is no longer necessary. The triangular waveforms with a repetition rate twice the frequency of the applied microwave signal can be directly generated by properly setting the bias and driven signal of the DPMZM. Since there is no additional optical processing, the proposed structure is cost effective. The repetition rate of the generated waveform is freely tunable over a wide bandwidth since there is no optical or electrical filter involved. The proposed approach is theoretically analyzed and experimentally demonstrated. Triangular waveforms with the repetition rates of 6, 8, and 10 GHz are successfully generated.

Progress in Optoelectronic Oscillators

An optoelectronic oscillator (OEO) generates a spectrally pure and ultra-stable radio frequency signal from a continuous wave laser source (Yao et al. 2004). In a conventional electrical oscillator, the energy storage capacity is limited, which compromises stability of the signal. To address this issue, Yao and Maleki invented the optoelectronic oscillator in 1996. This novel oscillator uses low-loss optical fiber to extend the length of the oscillator and thereby increases the amount of energy that can be stored (Madjar & Tibor 2006). Due to this additional energy storing component in the system, the purity and stability of the signal increase significantly. Following their invention, many modifications have been made over the years to improve the frequency stability of OEOs (lower phase noise and timing jitter). This review article discusses some of those key developments and then introduces some ongoing work devoted to understanding the impact of using electrical filters with Q >109.

High-Speed Light Sources in High-Speed Optical Passive Local Area Communication Networks

Abstract This study outlines the high-speed light sources in high-speed passive optical local area communication networks. Directly modulated laser measured is selected as a light source for data rate transfer of 40 Gb/s for propagation range up to 20 km. Optical output power after fiber-optic cable is measured. Signal power amplitude, Q-factor, and data error rates after the receive side are also measured. Hybrid optical amplifier, optical filters, and electrical filters are used for upgrading the network performance operation efficiency. The study assured that the optical communication network can be extended to 20 km distance with data rates of 40 Gb/s with achieving maximum Q-factor of 14.98 and minimum data rates of 3.55 ×10–51.

Modelling cascaded caloric refrigeration systems that are based on thermal diodes or switches

Solid state cooling based on caloric materials has a large potential, because there is no need for fluid refrigerants. The state of the art system approach relies on a heat transfer fluid, which is pumped back and forth through a regenerator of caloric material. This system approach has fundamental limitations regarding the cycle frequency. Different system approaches are considered. One is the utilization of fast thermal diodes or switches. The aim of this work is to provide a universal model to describe a cooling system based on caloric materials using thermal diodes or switches. The heat capacitance of the caloric material is defined to be constant, allowing a lumped elements representation. An analytical model based on an analogy to an electrical low pass filter is introduced. The analytical model is compared with good agreement to lumped elements simulations and measurement data from the literature. It is shown, that the newly introduced cut-off frequency as merit for the potential cycle frequency is proportional to the heat transfer coefficient of the diodes/switches in flux direction and inverse proportional to the length scale of the caloric material in heat flux direction. Different heat transfer mechanisms are discussed as basis for such thermal diodes and switches in combination with different caloric effects. To increase the cycle frequency compared to state of the art systems, latent heat transfer is a promising candidate for all caloric effects, whereas for example a dry press contact for a magnetocaloric system presents many challenges.

A Microwave Optoelectronic PLL Synthesizer Based on Optical Comb Reference

A tunable high-resolution synthesizer based on optoelectronic phase locked loop is proposed for the generation of microwave and mmWave frequencies. Optical modulation, frequency division, and phase locking processes are deployed to generate a tunable lower frequency exhibiting suppressed phase noise. Moreover, a dense tunable optical comb locked to the widely spaced reference is produced. A suite of microwave and mmWave frequencies in multiple frequency bands emerges from the beating of the generated optical frequency components and optical or electrical filtering may isolate the frequency bands of interest. The phase noise of the synthesized frequencies depends on the optical power of the input reference comb. The experimental evaluation, including Allan deviation and phase noise measurements, prove the high stability performance of the proposed scheme.

Laser-induced electrical signal filtering by multilayer reduced graphene oxide decorated with Au nanoparticles.

Nanoscale plasmonic particles represent a crucial transformation on optical and electronic properties exhibited by advanced materials. Herein are reported remarkable interferometric optical effects with dependence on polarization for filtering or modulating electronic signals in multilayer nanostructures. Metallic nanoparticles were incorporated in randomly distributed networks of reduced graphene oxide by an in-situ vapor-phase deposition method. The polarization-selectable nonlinear optical absorption contribution on the photoconductivity of reduced graphene oxide decorated with gold nanoparticles was analyzed. Nanosecond pulses at 532 nm wavelength were employed in a two-wave mixing experiment to study photoconduction and nonlinear optical absorption in this nanohybrid material. The ablation threshold of the sample was measured in 0.4 J/cm2. Electrochemical impedance spectroscopy measurements revealed a capacitive response that can be enhanced by gold decoration in carbon nanostructures. A strong two-photon absorption process characterized by 5 × 10-7 m/W was identified as a physical mechanism responsible for the nonlinear photoconductive behavior of the nanostructures. Experimental shift of 1 MHz for the cutoff frequency associated with an electrical filter function performed by the sample in film form was demonstrated. Moreover, amplitude modulation of electronic signals controlled by the polarization of a two-wave mixing experiment was proposed. All-optical and optoelectronic nanosystems controlled by multi-photonic interactions in carbon-based materials were discussed. The key role of the vectorial nature of light in two-wave mixing experiments is a fascinating tool for the exploration of low-dimensional systems.

Simple frequency-tunable optoelectronic oscillator using integrated multi-section distributed feedback semiconductor laser.

A novel approach to realizing an optoelectronic oscillator (OEO) based on an integrated multi-section (IMS) distributed feedback (DFB) laser is proposed and experimentally demonstrated. Our scheme adopts the method of direct modulation and a built-in microwave photonic filter (MPF), making the structure simpler and more flexible than an external modulator and electrical bandpass filter (EBPF). The IMS-DFB laser, which can overcome the drawbacks of using discrete lasers, is the key device in the scheme. Further, the two DFB sections, which are fabricated by Reconstruction Equivalent Chirp (REC) technique, are injected mutually. The SSB phase noise of the generated signal at the frequency of 20.3 GHz is -115.3 dBc/Hz@10kHz and -92.9 dBc/Hz@1kHz. The sidemode suppression ratio (SMSR) is 60.94 dB, which is a 40 dB improvement over a single loop. Furthermore, we demonstrate that the phase noise improves about 8 dB at the frequency offset of 1 kHz, when employing 13 km and 5.4 km fibers as the dual loop. The simple and compact structure, which consists of an IMS-DFB laser with high wavelength controlling accuracy and low process requirement, is a promising development for OEO integration.

Wideband tunable up-converting optoelectronic oscillator based on gain–loss compensation technology and stimulated Brillouin scattering

An optically wideband tunable up-converting optoelectronic oscillator (OEO) based on stimulated Brillouin scattering and gain–loss compensation is demonstrated and theoretically analyzed. In the proposed structure, Brillouin narrowband filter technique is implemented by introducing two pump lights with the frequency interval twice the Brillouin frequency shift (vb). The overlapping of the gain and the loss spectrum is used to realize a wideband tunable OEO. As a consequence, the tunability of the wideband of the output microwave signal at $$f_{m} + 2v_{b}$$ from 22.4 to 61.4 GHz can be realized by changing the signal under testing from 1 to 40 GHz. In addition, the transfer function of the system is given and the single sideband (SSB) phase noise is also evaluated theoretically. And the theoretical simulated the SSB phase noise is − 116.1 dBc/Hz at the 10 kHz offset when the fm = 25 GHz. Not only the OEO can convert a low-frequency IF signal to a high-frequency signal without introducing any high-Q electrical filter, but the frequency of the output signal is high enough and widely tunable. Because of the high frequency tunable capacity, the up-converting OEO might have a potential application in radar communication and millimeter wave generation systems.

MONITORING THE AFR OF THE INFORMATION SIGNAL FILTER OF A FLUX-GATE MAGNETOMETER ON THE EXAMPLE OF A SINGLE LINK BUTTERWORTH FILTER

The content of this paper relates to the field of monitoring the parameters of a magnetic field (MF) meter with a MF a fluxgate sensor. The article directly discusses the control method for the amplitude frequency response (AFR) of the second harmonic filter of an EMF fluxgate meter. The purpose of the work is to minimize the workplace (WP) equipment for magnetometer monitoring. We suggest an AFR monitoring method based on three readings. As an input signal source, while monitoring an AFR filter, we suggest the use of a WP fluxgate meter. The fluxgate meter is installed in a magnetic screen. The method consists in generating the filter input signal using the magnetometer. The essence of the suggested method is to analyze the AFR symmetry. As the base filter, we use a second-order Butterworth filter with a narrowband symmetric AFR. The effect of the electrical element filter ratings is systematized in the form of a correspondence table: an electric element – an AFR parameter. We present the AFR sufficiency control analysis in terms of its symmetry. The AFR monitoring, in terms of its symmetry, has been supplemented with the Kр(f0) monitoring using the personal computer. We demonstrate the peculiarities of using a fluxgate meter as an input signal source. We derived the ratio of the magnetometer electronic part parameters that affect the accuracy (discreteness) of the filter’s input signal generation. We present an algorithm with a description of the magnetometer operation in the AFR monitoring mode.

Photonic generation of background-free binary phase-coded microwave pulses.

We report a photonic scheme to generate background-free frequency-doubled binary phase-coded microwave pulses. The key component is a dual-polarization dual-parallel Mach-Zehnder modulator that is used to realize phase modulation and carrier-suppressed double second-order sideband modulation at two orthogonal polarization states, respectively. The π phase jump of the frequency-doubled phase-coded microwave pulse is dependent on the polarity of the coding signal rather than its amplitude. Besides, the generated microwave pulses are free from the baseband-modulated signals, because the optical power launched to a photodetector (PD) keeps constant all the time. Since no electrical or optical filters are involved, the photonic generator can ensure a broad operation bandwidth and wide tunability. Our scheme is theoretically analyzed and experimentally verified. The 4Gb/s at 16GHz and 7Gb/s at 28GHz background-free frequency-doubled phase-coded microwave pulses have been successfully generated.

Tunable optoelectronic oscillator working in the Ku band

An improved tunable optoelectronic oscillator (OEO) based on a dual-parallel Mach–Zehnder (MZ) modulator embedded with a sub-MZ modulator is designed and experimentally demonstrated for Ku band applications. Single-mode oscillator operation is achieved with a single feedback loop and without any electrical filters, which improves the tunability of the proposed OEO. The microwave power expression at the output of photodetector is developed using the well-known Taylor series expansion method to calculate the electrical spectrum and accumulated dispersion (ps nm−1) of the dispersive element (linearly chirped fiber Bragg grating). Phase noise is also examined, which allows us to conclude that our proposed oscillator is suitable for optical wireless communication, radar and phase array antenna applications. Furthermore, its application as a strain and temperature sensor is investigated and it is found to have maximum strain sensitivity (Kε) of 58.75 MHz με−1 and temperature sensitivity (KT) of 1.752 GHz °C−1.

Photonic Generation of Ultra-Wideband Signal by Truncating a Continuous Wave into a Pulse

We propose and demonstrate a background-free millimeter-wave (MMW) ultra-wideband (UWB) signal generator using a dual-polarization dual-parallel Mach–Zehnder modulator. The MMW-UWB signal is generated by truncating a continuous-wave (CW) radio-frequency (RF) signal into an RF pulse. The upper dual-parallel Mach–Zehnder modulator (DPMZM1) is properly set to act as a phase modulator, while the lower DPMZM2 is well biased to generate a carrier-suppressed double-sideband (CS-DSB) modulated signal. By shifting the phase of the optical carrier through DPMZM1, a CW RF signal is truncated into a pulse one in a photodetector (PD). The baseband frequency components and local oscillator signal are well suppressed, since the optical power sent to the PD is constant. Moreover, there is no optical or electrical filters involved, which ensures a broad operation bandwidth and wide tunability. The proposed scheme is theoretically analyzed and experimentally verified. The generated background-free UWB signal at an RF carrier frequency of 26 GHz meets well the Federal Communications Commission spectral mask for outdoor UWB systems.

Twin-SSB-OFDM Transmission Over Heterodyne W-Band Fiber-Wireless System With Real-Time Implementable Blind Carrier Recovery

We experimentally demonstrate a heterodyne W-band fiber-wireless system using a twin single-side-band orthogonal frequency division multiplexing (Twin-SSB-OFDM) transmission scheme with low-cost electrical filters. The transmission scheme is proposed to halve the required sampling rate of the baseband receiver. Moreover, since the W-band signal generation is based on optical heterodyne with nonideal laser sources, there is a time-varying carrier frequency offset (CFO) in the system. To mitigate the CFO effect and simultaneously realize down-conversion, a blind carrier recovery method is proposed and validated in the system. The experimental results show that after 22-km SSMF transmission and 1-m wireless transmission, the system can achieve a 40.07 Gb/s data rate with a bit-error-ratio (BER) below 3.8 × 10−3 when using a two-channel 12-GSa/s arbitrary waveform generator (AWG) as transmitter and two emulated 12-GSa/s baseband receivers. In addition, by setting the AWG at 5-GSa/s and using a 5-GSa/s real-time field programmable gate array (FPGA)-based receiver, an additional experiment is carried out by implementing the proposed method in the real-time receiver. Although the frequency swing of the intermediate frequency (IF) carrier of the received signal is up to ∼300 MHz, the system can also achieve a relatively stable transmission performance. The additional experiment further verifies the effectiveness and practical feasibility of the proposed carrier recovery method and the Twin-SSB-OFDM transmission scheme.

Optical Communication Using Linear Sums of Optical Receiver Modes: Proof of Concept

We demonstrate the feasibility of an optical communication system that transmits linear sums of optical receiver modes (ORMs) as optical signals called ORM signals. The ORMs are inherent modes of conventional direct-detection optical receivers for wavelength-division multiplexing systems. Two lowest order ORMs are used to build ORM signals having distinct received voltage waveforms from each other. The optical receiver used has a Fabry–Perot filter as its optical filter and a fourth-order Bessel filter as its electrical filter. With these filters, corresponding ORMs are evaluated numerically and the ORM signals are generated using digital-to-analog converters. The received voltage waveforms after the receiver electrical filter are in good agreement with our analysis.