Modulated Optical Signal Research Articles

Modulation of propagating surface plasmons

The diffraction limit of light greatly limits the development of conventional optical devices, which are difficult to be miniaturized and integrated with high density. Surface plasmons, electromagnetic modes at the metal-dielectric interface, can concentrate light into deep subwavelength dimensions, enabling the manipulation of light at the nanometer scale. Surface plasmons can be used as information carrier to transmit and process optical signals beyond the diffraction limit. Therefore, nanodevices based on surface plasmons have received much attention. By modulating surface plasmons, the modulation of optical signals at nanoscale can be realized, which is important for the development of on-chip integrated nanophotonic circuits and optical information technology. In this article, we review the modulations of propagating surface plasmons and their applications in nano-optical modulators. The wave vector of propagating surface plasmons is very sensitive to the dielectric function of the metal and the environment. By tuning the dielectric function of the metal and/or the surrounding medium, both the real and imaginary part of the wave vector of surface plasmons can be modified, leading to the modulation of the phase and propagation length of surface plasmons and thereby modulating the intensity of optical signals. We first introduce the basic principles of different types of modulations, including all-optical modulation, thermal modulation, electrical modulation, and magnetic modulation. The all-optical modulation can be achieved by modulating the polarization and phase of input light, pumping optical materials, changing the dielectric function of metal by control light, and manipulating a nanoparticle by optical force to modulate the scattering of surface plasmons. The modulation based on thermal effect depends on thermo-optic materials and phase-change materials, and the temperature change can be triggered by photothermal effect or electrical heating. For electrically controlled modulation, Pockels electro-optic effect and Kerr electro-optic effect can be employed. Electrical modulation can also be realized by controlling the carrier concentration of semiconductors or graphene, using electrochromatic materials, and nanoelectromechanical control of the waveguide. The modulation of surface plasmons by magnetic field relies on magneto-optic materials. We review recent research progresses of modulating propagating surface plasmons by these methods, and analyze the performances of different types of plasmonic modulators, including operation wavelength, modulation depth or extinction ratio, response time or modulation frequency, and insertion loss. Finally, a brief conclusion and outlook is presented.

Demodulation of optical eigenvalue modulated signals using neural networks

Demodulation of optical eigenvalue modulated signals using neural networks

直接探测系统中两种单边带光信号调制与恢复方法的研究

直接探测系统中两种单边带光信号调制与恢复方法的研究

All-optical modulation format conversion from PSK to ASK based on phase-sensitive amplification

With the development of the optics communication system and optical signal modulation technology, the amplitude-shift keying (ASK) and phase-shift keying (PSK) are both used in different optical communication sub-networks. In this paper, a novel all-optical modulation format from PSK to ASK based on phase-sensitive amplification is proposed and demonstrated. Using the nonlinear interference of the single-pump phase-sensitive amplification, the signal wavelength can be preserved while the modulation format is conversed. The proposed scheme provides the flexible intermediate node interface transformation in future optical networks.

Wideband optical vector network analyzer based on polarization modulation

We propose a polarization modulator (PolM) -based optical vector network analyzer (OVNA) with extended measurement bandwidth. The combined use of the PolM, a polarization controller (PC) and a polarizer performs phase-and-intensity hybrid modulation of optical signal with double-sideband (DSB) modulation. The ratio between phase and intensity modulations is controlled by the PC, leading to different modulation formats. The frequency response of a device-under-test (DUT) can be obtained by processing the results of two measurements under two arbitrarily different modulation formats. The significance of this work lies in that the measurement of a DUT with bandpass response can be simply achieved, which is a huge challenge for the conventional single-sideband (SSB)-based OVNAs. In addition, the measurement bandwidth is doubled compared with the conventional SSB-based OVNA. Moreover, the PolM-based OVNA can avoid the bias drifting problem using conventional Mach–Zehnder modulator (MZM)-based scheme. The proposed method is theoretically and experimentally demonstrated. A proof-of-concept experiment is carried out and a DUT with bandpass response is successfully measured using the proposed scheme.

All-optical DNA variant discovery utilizing extended DV-curve-based wavelength modulation.

This paper presents a novel optical processing approach for exploring genome sequences built upon an optical correlator for global alignment and the extended dual-vector-curve (DV-curve) method for local alignment. To overcome the problem of the traditional DV-curve method for presenting an accurate and simplified output, we propose the hybrid amplitude wavelength polarization optical DV-curve (HAWPOD) method, built upon the DV-curve method, to analyze genome sequences in three steps: DNA coding, alignment, and post-analysis. For this purpose, a tunable graphene-based color filter is designed for wavelength modulation of optical signals. Moreover, all-optical implementation of the HAWPOD method is developed, while its accuracy is validated through numerical simulations in LUMERICAL FDTD. The results express that the proposed method is much faster than its electrical counterparts.

160-GBd (320-Gb/s) PAM4 Transmission Using 97-GHz Bandwidth Analog Multiplexer

We demonstrate the transmission of a single-polarization four-level pulsed amplitude modulation (PAM4) optical signal over 10-km single-mode fiber at the gross bit rate of 320 Gb/s and the net data rate of 266.7 Gb/s. A digital-preprocessed analog-multiplexed digital-to-analog converter with a 97-GHz bandwidth analog multiplexer module enables us to generate the Nyquist-shaped PAM4 signal at the high baud rate of 160 Gbd.

Analysis of amplification in a fiber ring resonator with a fabry‐perot cavity

AbstractThe placement of an Erbium‐doped Fiber Amplifier and a Fabry‐Perot cavity inside a fiber ring resonator can generate a sinusoidal modulation in the optical signal obtained. The characterization of this behavior is achieved by changing the length of the Fabry‐Perot cavity, which acts as a sensing device. A theoretical model of the optical signal modulation obtained with such configuration is also presented.

Experimental demonstration of 4-PAM for high-speed indoor free-space OW communication based on cascade FIR-LMS adaptive equalizer

Inter-symbol interference (ISI) is one of the key problems that seriously limit the transmission data rate in optical communication system. To eliminate ISI and further improve the system performance, we design a specific cascade finite impulse response-least mean square (FIR-LMS) equalizer. To the best of our knowledge, it is the first time this kind of equalizer is employed for high-speed indoor free-space optical wireless (OW) communication system. After LD driver printed circuit board (PCB) validated the design, a special miniaturized and inexpensive LD, and a spatial photodetector are employed at the transmitter and receiver, respectively. Based on these, we experimentally investigate the scheme of 4-pulse amplitude modulation (4-PAM) optical signal combined with cascade FIR-LMS adaptive equalizer in an indoor free-space OW communication system. The convergence performance between LMS and FIR-LMS is compared, the bit error rate (BER) performances of FIR, LMS and FIR-LMS equalizer at different propagation distances are also demonstrated. With the utility of the proposed equalizer, the OW communication system can successfully achieve the bit rate 10 Gbit/s transmission over 500 cm indoor free-space link distance. The BER significantly below the 7% forward error correction (FEC) limit of 3.8×10−3, which is lower than LMS by more than an order of magnitude.

Dual-Output Mach–Zehnder Modulator for Optical Access Networks

ABSTRACTThis paper employs dual-output Mach–Zehnder Modulator (MZM) for optical access networks without optical filters. Light waves generated from multiple laser sources are multiplexed and fed into dual-output MZM. Biasing the dual-output MZM at null point generates central carriers in one output port and first-order sidebands in another output port. Reflective semiconductor optical amplifier modulates both the central carriers and sidebands with wired and wireless data, respectively. The modulated optical signals are combined by polarization beam splitter and transmitted through 25-km single-mode fiber. The performance of the proposed scheme is proved by clear eye-diagrams and great bit error rate (BER) curves. Moreover, the power penalty at the BER of 10-9 is less than 1 dB for both wired and wireless signals. Therefore, the proposed system simultaneously transmits wired and wireless signals.

Observation of guided acoustic-wave Brillouin scattering noise and its compensation in digital coherent optical fiber transmission.

We describe the first observation of guided acoustic-wave Brillouin scattering (GAWBS) phase noise in a digital coherent optical fiber transmission. GAWBS noise, which is a forward lightwave generated by thermally excited vibration modes in a cylindrical fiber structure, occurs coherently not only in a signal at a single carrier frequency, but also in modulated wide-band optical signals. Since the signal-to-GAWBS-noise ratio is independent of signal power, it has caused problems in various fields including quantum optics. We point out that GAWBS noise exists even in a digital coherent transmission system such as quadrature amplitude modulation (QAM) and degrades the transmission performance since the phase noise is inevitably included within the bandwidth of the transmitted data. We propose two analogue and one digital method to compensate for the GAWBS noise and demonstrate improved performance in a QAM digital coherent transmission.

Experimental demonstration of a 16.9 Gb/s link for coherent OFDM PON robust to frequency offset and timing error

Due to its merits of flexible bandwidth allocation and robustness towards fiber transmission impairments, coherent optical orthogonal frequency division multiplexing (CO-OFDM) technology draws a lot of attention for passive optical networks (PON). However, a CO-OFDM system is vulnerable to frequency offsets between modulated optical signals and optical local oscillators (OLO). This is particularly serious for low cost PONs where low cost lasers are used. Thus, it is of great interest to develop efficient algorithms for frequency synchronization in CO-OFDM systems. Usually frequency synchronization proposed in CO-OFDM systems are done by detecting the phase shift in time domain. In such a way, there is a trade-off between estimation accuracy and range. Considering that the integer frequency offset (IFO) contributes to the major frequency offset, a more efficient method to estimate IFO is of demand. By detecting IFO induced circular channel rotation (CCR), the frequency offset can be directly estimated after fast Fourier transforming (FFT). In this paper, circular acquisition offset frequency and timing synchronization (CAO-FTS) scheme is proposed. A specially-designed frequency domain pseudo noise (PN) sequence is used for CCR detection and timing synchronization. Full-range frequency offset compensation and non-plateau timing synchronization are experimentally demonstrated in presence of fiber dispersion. Based on CAO-FTS, 16.9 Gb/s CO-OFDM signal is successfully delivered over a span of 80-km single mode fiber.

A hybrid WDM ring–tree topology delivering efficient utilization of bandwidth over resilient infrastructure

This paper proposed a hybrid WDM ring---tree topology which employs spectrally efficient 60 Gbps non-return-to-zero/polarization shift keying optical orthogonal modulated signals. The reconfigurable optical add/drop multiplexers, optical cross-connects and semiconductor optical amplifiers are utilized to make hybrid ring---tree architecture. Each optical add/drop multiplexer node is connected to tree topology to further increase the number of users. The main contribution of the proposed spectrally efficient hybrid optical network is to support the maximum number of users within limited bandwidth for future communication networks. Also, the proposed resilient ring---tree architecture has advantages such as high optical node density and bandwidth/spectral efficiency as compared to conventional packet-switched optical access network.

湍流信道下光空间调制信号的压缩感知检测

湍流信道下光空间调制信号的压缩感知检测

A Simple Technique for Triangular Waveform Generation based on a Dual-Polarisation Modulator

A new microwave photonic topology for generating a triangular waveform is presented. The concept is based on incoherent summation of two intensity modulated optical signals to generate the first- and third-order harmonic frequency components with the same amplitude and phase as that of an ideal triangular waveform. The proposed triangular waveform generator has a very simple and low-cost structure as it only requires the Mach Zehnder modulator in a conventional fiber optic link to be replaced by an integrated dual-polarization modulator driven by two 90° phase difference RF signals. It also has a widely tunable repetition rate, low insertion loss, and a stable performance. Experimental results demonstrate a triangular waveform with a tunable microwave-frequency repetition rate and a root mean square error value of <;0.049 when comparing with an ideal triangular waveform. The stability of the proposed triangular waveform generator is also examined experimentally.

Secured RoF segment in subterahertz range providing independent optical modulation of radiochannel frequency characteristics and phased antenna array beamsteering parameter

Design principles are proposed for a secure subterahertz RoF segment providing independent optical modulation by radiochannel frequency characteristics and a phased antenna array beamsteering parameter. A design scheme of the RoF segment for the W-range is proposed. The results obtained include co-transmission of two modes (one of which is polarized), radio channel frequency properties control, orbital angular momentum signal shaping, co-transmission of a modulated optical signal and a polarized signal and orbital angular momentum signal. Simulation is carried out for signals with a given spin-orbit state based on a Hamiltonian approach. Results of a phase-amplitude filter calculation are presented.

Wide-angle absorption of visible light from simple bilayers.

Color-selective absorption of light is a very significant operation used in numerous applications, from photonic sensing and switching to optical signal modulation and energy harnessing. We demonstrate angle-insensitive and polarization-independent absorption by thin bilayers comprising ordinary bulk media: dielectrics, semiconductors, and metals. Several highly efficient designs for each color of the visible spectrum are reported, and their internal fields' distributions reveal the resonance mechanism of absorption. The proposed bilayer components are realizable, since various physical or chemical deposition methods can be used for their effective fabrication. The absorption process is found to exhibit endurance with respect to the longitudinal dimension of the planar structure, which means that the same designs could be successfully utilized in non-planar configurations composed of arbitrary shapes.

Thermomechanically Tunable Infrared Metamaterials Using Asymmetric Split-Ring Resonators

We demonstrate a nanoelectromechanical systems-based tunable infrared metamaterial formed with an array of Au/Si bilayer split-ring resonators having two asymmetric arms. The wider arm of the resonator is anchored on the substrate, while the thinner one is free to bend in vertical direction by varying temperature. The bending of the thin arm changes the air gap between the two arms, and thus modulates the optical resonance modes of the resonator. The presented tunable metamaterial has an ultra-small footprint size and provides a relatively large optical signal modulation at 3.6- $\mu \text{m}$ wavelength.

NEMS-Based Infrared Metamaterial via Tuning Nanocantilevers Within Complementary Split Ring Resonators

Dynamic control of the electromagnetic properties of metamaterials requires wide modulation bandwidth. Tunable metamaterials with large tunability and fast speed are thus highly desirable. Due to the small dimensions, subwavelength meta-atoms or resonant elements that constitute a metamaterial in the mid-to-near-infrared (IR) wavelength range are often not easy to be tuned at a high rate of several tens of megahertz (MHz). Here, we report on a nanoelectromechanical systems (NEMS)-based tunable IR metamaterial realized by unique embedding of nanocantilevers into complementary split ring resonators (c-SRRs) suspended over individual wells. The optical field confined in the air gap of the c-SRR is strongly influenced by electrostatically induced mechanical deflection of the nanocantilever, thus modulating the reflection spectrum of the metamaterial. With the easy-to-implement tunable meta-atom design, the IR metamaterial with 800-nm-long cantilevers provides an ultrahigh mechanical modulation frequency of 32.26 MHz for optical signal modulation at a wavelength of 2.1 $\mu \text{m}$ , and is rather easy to manufacture and operate. We envision a compact, efficient, and high-speed electrooptic modulation platform in the IR region using this NEMS tunable metamaterial technology. [2017–0012]

Microwave Photonic Frequency Tripler Based on an Integrated Dual-Parallel Modulator Structure

A new technique for tripling the frequency of a microwave signal is presented. It is based on an integrated dual-parallel Mach–Zehnder modulator, which generates two orthogonally polarised RF modulated optical signals with different modulation indexes, and a polarisation-dependent optical attenuator. The photodetector output fundamental RF components generated by the two orthogonally polarised RF modulated optical signals have the same amplitude but an opposite phase, which are cancelled, leaving the frequency tripled microwave signal and the unwanted fifth order harmonic. The new frequency tripler has a simple structure, a wide bandwidth, and a high electrical spurious suppression ratio. Experimental results are presented demonstrating three times frequency multiplication of different-frequency microwave signals with electrical spurious suppression ratio of over 20 dB. The phase noise and the stability performance of the frequency tripler are also investigated experimentally.