Single Sideband Signal Research Articles

New Negentropy Optimization Schemes for Blind Signal Extraction of Complex Valued Sources

Blind signal extraction, a hot issue in the field of communication signal processing, aims to retrieve the sources through the optimization of contrast functions. Many contrasts based on higher-order statistics such as kurtosis, usually behave sensitive to outliers. Thus, to achieve robust results, nonlinear functions are utilized as contrasts to approximate the negentropy criterion, which is also a classical metric for non-Gaussianity. However, existing methods generally have a high computational cost, hence leading us to address the problem of efficient optimi- zation of contrast function. More precisely, we design a novel reference-based contrast function based on negentropy approximations, and then propose a new family of algorithms (Alg. 1 and Alg. 2) to maximize it. Simula- tions confirm the convergence of our method to a separat- ing solution, which is also analyzed in theory. We also vali- date the theoretic complexity analysis that Alg. 2 has a much lower computational cost than Alg. 1 and existing optimization methods based on negentropy criterion. Finally, experiments for the separation of single sideband signals illustrate that our method has good prospects in real-world applications.

Dynamic range improvement of broadband microwave photonic links using a linearized single-sideband modulator

A novel linearized single-sideband modulator is proposed and demonstrated to generate optical single-sideband (OSSB) signal and improve the dynamic range of microwave photonic links. The modulator is composed of a dual-electrode Mach–Zehnder modulator (DEMZM) lying on the top branch and a phase shifter (PS) lying on the bottom branch. By optimizing the optical power split ratio of the linearized modulator and the phase shift of the PS, the third-order inter-modulation distortion (IMD3) can be efficiently suppressed while the second-order distortion components are eliminated simultaneously. It is a multi-octave linearization technique which can be applied for broadband systems. Simulation results show that, the linearized modulator can provide a spurious-free dynamic range (SFDR) of 130dB for a bandwidth of 1Hz at the received optical power of 2dBm assuming shot noise is the dominant noise contribution, which is 22dB higher than the conventional DEMZM. The effects of the finite extinction ratio of modulator, the phase deviation of PS and the dispersion of fiber on the linearization performance are also investigated.

Optimum Bias Point in Broadband Subcarrier Multiplexing With Optical IQ Modulators

This paper develops a theoretical analysis of the tradeoff between carrier suppression and nonlinearities induced by optical IQ modulators in direct-detection subcarrier multiplexing systems. The tradeoff is obtained by examining the influence of the bias conditions of the modulator on the transmitted single side band signal. The frequency components in the electric field and the associated photocurrent at the output of the IQ modulator are derived mathematically. For any frequency plan, the optimum bias point can be identified by calculating the sensitivity gain for every subchannel. A setup composed of subcarriers located at multiples of the data rate ensures that the effects of intermodulation distortion are studied in the most suitable conditions. Experimental tests with up to five QPSK electrical subchannels are performed to verify the mathematical model and validate the predicted gains in sensitivity.

A single sideband radio-over-fiber system with improved dynamic range incorporating a dual-electrode dual-parallel Mach–Zehnder modulator

A novel single sideband (SSB) radio-over-fiber (ROF) system based on a dual-electrode dual-parallel Mach–Zehnder modulator (DE-DPMZM) is proposed, in which the Mach–Zehnder modulator (MZM) is used to produce a single sideband signal and the dual-parallel structure is used to suppress the third-order intermodulation distortion (IMD3) to improve the spurious-free dynamic range (SFDR) of the ROF system. A theoretical analysis is given and simulation experiment is carried out. The results show that the proposed scheme can improve 25dB in SFDR which is up to 127.854dBHz2/3 compared with the conventional SSB ROF system. In addition, the single sideband modulation can extend the transmission distance of optic signal.

The Dual-Electroabsorption Modulated Laser, a Flexible Solution for Amplified and Dispersion Uncompensated Networks Over Standard Fiber

We propose here a monolithically integrated dual RF access electroabsorption-modulated laser called D-EML for the generation of optical single-sideband signal for both nonreturn to zero and orthogonal frequency division multiplexing formats. The benefits of optical single-sideband over double sideband in terms of resilience against chromatic dispersion effects are presented for high-bit rate intensity modulation/direct detection transmissions over standard single mode fiber in the C-band. Both simulation and experimentation exhibit transmission distance enhancement in the case of dual modulation of the D-EML, i.e., in optical single-sideband configuration, making this optical source an interesting solution because of its low-cost, low-size, and reasonable-power consumption.

Accuracy improvement of optical vector network analyzer based on single-sideband modulation.

An approach to suppress the measurement errors induced by the high-order sidebands of the optical single-sideband (OSSB) signal in the OSSB-based optical vector network analyzer (OVNA) is proposed and experimentally demonstrated. An analytical model for studying the measurement errors of the OSSB-based OVNA is established. Results show that the measurement errors introduced by the high-order sidebands can be obtained by suppressing the optical carrier in the OSSB signal. By subtracting these errors from the ordinary frequency responses measured by the OVNA, accurate frequency responses can be achieved. A proof-of-concept experiment is performed. The magnitude and phase responses of a fiber Bragg grating are measured with good coincidence by the OSSB signals with different modulation indices.

Simple ku‐band radio over fiber system with high‐dispersion tolerance using a polymer‐based microring resonator filter

AbstractThis article presents an optical single sideband (SSB) signal generation in radio over fiber system using a polymeric microring resonator as an optical notch filter, alleviating the fiber chromatic dispersion‐induced carrier fading problem. With this technique, optical SSB radio frequency (RF) signal with a RF frequency of 14.35 GHz carrying 40‐Mbps quadrature phase shift keying vector signal is generated. This signal is transmitted over 25‐km standard single‐mode fiber successfully, and the received signal error vector magnitude is 5.8% rms. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1129–1133, 2014

Performance improvement of double-sideband signals in radio-over-fiber links utilizing pre-distortion method

In this paper, we investigate the optimal carrier-to-sideband ratio (CSR) for optical double-sideband (DSB) signals in radio-over-fiber (RoF) transmission. A pre-distortion method based on spectral shaping is proposed to optimize the signal CSR and eliminate the dispersion-induced power fading. A 12 GHz RoF transmission over 29 km standard single mode fiber (SSMF) is experimentally demonstrated which reveals that pre-distorted DSB has a 4.4 dB improvement over the one without pre-distortion, and 1.2 dB sensitivity advantage over single sideband (SSB) both with optimal CSR. The pre-distortion method is also applied to multi-channel transmission. The multi-channel experiment shows that for all channels the dispersion-induced power fading effects can be simultaneously mitigated and the pre-distorted DSB signals have ~1 dB sensitivity improvement over the SSB signals.

Simultaneous monitoring of first-order polarization mode dispersion and chromatic dispersion based on RF power detection technique

We propose a novel technique for independent and simultaneous monitoring of first-order polarization mode dispersion (PMD) and chromatic dispersion (CD). For PMD monitoring, radio frequency (RF) power is detected after asymmetric filtering by a band-stop filter (BSF). The RF tone power ratio (PR) of the double sideband (DSB) to the single sideband (SSB) signal components is utilized for CD monitoring. We discuss the performance for 80Gb/s NRZ-DQPSK signal by simulation. Simultaneous monitoring of 246.7ps/nm CD with a 22.3dB dynamic range (DR) and 50ps differential group delay (DGD) with a 42.7dB DR can be realized at 10GHz detection band. When only CD is monitored, the detection frequency can be further decreased to 5GHz, where the monitoring range (MR) is 356ps/nm and DR is 30.5dB. The influences of other parameters, such as the BSF offset, the bandwidths of BSF and electrical-band-pass-filter (EBPF), the filter shape, and the modulation rate and format, are investigated in the paper.

Tunable multi-tap microwave photonic filter with complex coefficients using a dual-parallel Mach–Zehnder modulator

We propose and demonstrate a tunable multi-tap microwave photonic filter (MPF) with complex coefficients. It is based on addition of carrier suppressed single sideband (CS-SSB) signal and phase-controllable optical carrier. Instead of using the technique of optical filtering, the CS-SSB signal is generated by a dual-parallel Mach–Zehnder modulator (DPMZM) in our scheme. Frequency tuning of the filter is achieved by changing the phase of the optical carrier, which can be controlled by a variable optical delay line (VDL). The proposed structure features high flexibility and wideband RF response, and the experimental results demonstrate that it can be tuned continuously over one free spectral range (FSR) without changing the spectral shape of the filter.

An Ultra-Wideband Microwave Photonic Phase Shifter With a Full 360$^{\circ}$ Phase Tunable Range

A novel photonic approach to the implementation of an ultra-wideband microwave phase shifter is proposed and experimentally demonstrated. In the proposed system, a single-sideband (SSB) signal is sent to a polarization-maintaining fiber Bragg grating (PM-FBG), which has two spectrally separated transmission notches along the fast and the slow axes. By locating the optical carrier along the fast axis at the transmission notch, the optical carrier in the SSB signal is removed. At the output of the PM-FBG, two orthogonally polarized optical signals, one with the optical carrier and the sideband, the other with only the sideband, are obtained. The two orthogonal signals are then sent through a variable retardation plate (VRP) to a polarizer and then detected by a photodetector. By controlling the VRP to introduce a tunable phase difference between the two orthogonally polarized SSB signals, a microwave signal with a tunable phase shift is generated. A theoretical analysis is developed, which is validated by an experiment. A microwave phase shifter with a full 360° phase shift over a frequency range from 10 to 40 GHz is demonstrated.

A Novel Approach to Realizing SSB Modulation With Optimum Optical Carrier to Sideband Ratio

A novel approach to realizing single sideband (SSB) modulation with optical carrier to sideband ratio (OCSR) of 0 dB, which is optimum for maximizing the transmission performance of a radio-over-fiber system, is proposed and experimentally demonstrated based on a strong optical injection-locked distributed feedback (DFB) laser. Tunable OCSR with optimum value of 0 dB is achieved by tuning the injection ratio and the detuning frequency precisely. A simulation is carried out to confirm the optimum OCSR. Gain properties of the DFB laser under strong optical injection are also measured for the first time to our knowledge. Doubled frequency of the LO signal is obtained without any filter. The generated optical SSB signal of 20 GHz is transmitted over 60-km single-mode fiber experimentally; results show it is almost not affected by the fiber chromatic dispersion.

A Study on the Demodulation of Four Single Sideband Signals in Multi-carrier Systems

A Study on the Demodulation of Four Single Sideband Signals in Multi-carrier Systems

Ultracompact ring resonator microwave photonic filters based on photonic crystal waveguides

We design two microwave photonic filters (notch filter and bandpass filter) based on silicon on insulator (SOI) photonic crystal waveguides for a 60 GHz single-sideband signal radio-over-fiber (ROF) system. By perturbing the radii of the first two rows of holes adjacent to the photonic crystal waveguide, we obtained a broad negligible dispersion bandwidth and a corresponding constant low group velocity. With the slow light effect, the delay line of filters can be significantly reduced while providing the same delay time as fiber based delay lines. The simulation results show that the delay-line length of the notch filter is only about 25.9 μm, and it has a free spectral range of 130 GHz, a baseband width (BW) of 4.12 GHz, and a notch depth of 22 dB. The length of the bandpass filter is 62.4 μm, with a 19.6 dB extinction ratio and a 4.02 GHz BW, and the signal-to-noise ratio requirement of received data can be reduced by 9 dB for the 10(-7) bit-error ratio. Demonstrated microwave photonic crystal filters could be used in a future high-frequency millimeter ROF system.

Optical up-converted single-sideband generation using intensity modulators and fiber gratings

A novel method is proposed for optical up-converted single-sideband (OSSB) signal generation in radio over fiber links, which can realize optical carrier reuse synchronously. The OSSB signal is generated in order to overcome the fiber dispersion problem by using two intensity modulators in combination with fiber gratings. With this up-conversion technique, a 25 GHz OSSB radio frequency signal is generated by mixing an intermediate frequency signal (5 GHz) and low frequency local oscillator signal (10 GHz). The signal is transmitted over 25 km standard single-mode fiber successfully. And the received signal error vector magnitude is 5.8% root mean square, with eye diagram widely open.

Performance optimization of radio-on-fiber systems employing erbium doped fiber amplifier for optical single sideband signals considering intermodulation distortion

The performances of radio on fiber (RoF) systems with a dual-electrode Mach-Zehnder modulator and an erbium-doped fiber amplifier (EDFA) are optimized by numerical equations including the third order intermodulation (IM3) as well as amplified spontaneous emission (ASE) noise. We investigate a signal-to-noise-and-distortion ratio (SNDR) considering fiber dispersion with respect to an input signal power and an EDFA gain in both noise-dominant and third order intermodulation (IM3)-dominant cases. We also verify that the numerical analysis results are well matched with those of a commercial simulator, VPItransmissionMaker. In the analysis results, the optimum input signal power for the maximum SNDR of a RoF system with EDFA was reduced over 8 dB compared with that without EDFA. The dramatic reduction of IM3 power at a receiver was resulted from this decrement of input signal power. Thus, the maximum SNDR of the system with EDFA was obtained over 17 dB at 40 km fiber compared with that of the system without EDFA. In addition, the results showed that the SNDR was efficiently improved by EDFA in the noise-dominant case, while the SNDR improvement was negligible by EDFA in the IM3 dominant case.

Optical single sideband modulation of 60-GHz radio over fiber (ROF) system using ultra compact photonic crystal ring-shaped channel drop filter

An ultra compact photonic crystal (PC) ring-shaped channel drop filter (RSCDF) is proposed to generate single side band (SSB) signal for 60GHz ROF system. This PC-RSCDF contains a bus waveguide, a resonant cavity, a ring-shaped waveguide (RSW) and a coupled cavity output waveguide. The notch depth and notch bandwidth of CDF can get 98% and 0.4nm respectively by inducing RSW and shifting the center defect rod of cavity and the rod around the cavity. Then, a method of fine tuning the resonant frequency of PC-RSCDF is proposed by adjusting the radius of insensitive rods which have weak coupling interaction with the light and the sensitivity of structure can be decreased, and the resonant frequency can be shifted to the sideband frequency of double side band (DSB) signal accurately. Finally, a 60GHz ROF SSB modulation system is demonstrated by using designed PC-RSCDF that can filter lower or upper sideband by changing its structure parameters. The extinction ratio (ER) of lower and upper sideband can get 20.9dB and 18.6dB respectively.

Received Power performance in downlink architecture of Radioover-Fiber Transmission system using OSSB Techniquedue to chromatic dispersion and laser linewidth

The In this paper, we studied the RoF system and analyzed the received power performance in downlink architecture of RoF system. The RoF system employs a Mach-Zehnder modulator (MZM) and a phase shifter to externally generate an optical single sideband (OSSB) signal since the OSSB signal is tolerable for power degradation due to a chromatic fiber-dispersion effect. The received power performance is analyzed by calculating a factor called Power Penalty. It is shown that Power penalty is increased exponentially as the differential delay increased with the distance due to chromatic dispersion with the change in laser linewidth

Active stabilisation of single drive dual‐parallel Mach‐Zehnder modulator for single sideband signal generation

Presented is a study on a single-drive dual-parallel Mach-Zehnder modulator implementation as a single sideband suppressed carrier generator. High values of both extinction ratio and sidemode suppression ratio were obtained at different modulation frequencies over the Cband. In addition, a stabilisation loop had been developed to preserve the single sideband generation over time. © The Institution of Engineering and Technology 2013.

Perfectly Orthogonal Optical Single-Sideband Signal Generation Based on Stimulated Brillouin Scattering

We experimentally demonstrate a perfectly orthogonal optical single-sideband signal generation technique using stimulated Brillouin scattering. By using both the Brillouin gain and loss, a perfectly orthogonal optical single-sideband signal is achieved. In addition, the modulation depth of the single-sideband signal is adjustable by separately tuning the gain and loss for the optical carrier.