SSB Modulation Research Articles

Analysis of Transmission Characteristics with Improved Modulation Formats Based on ROF Coherent System

Abstract Radio over Fiber (RoF) is one of the solutions to the “last mile” because of its bandwidth advantage offered by fiber and the mobility and flexibility of wireless systems. In this paper, the transmission performance of DSB, SSB and OCS with three modulation formats is established, and a new single-sideband modulation single-mode optical fiber transmission model is proposed, and simulated analysis is done to the system. In this paper, 40 GHz millimeter-wave signal was generated by external modulation, and the received signal is received by coherent demodulation. In this paper, Matlab and VPI are used for combine programming simulation, DCF method was used to compensate the chromatic dispersion. Through the analysis of dispersion performance, Q value and bit error rate, we can see that the modified SSB modulation has the best transmission performance for 120 km links.

High performance photonic microwave frequency down-conversion using a dual-drive dual-parallel Mach-Zehnder modulator

ABSTRACTPhotonic microwave frequency down-conversion based on carrier suppression single sideband (CS-SSB) modulation via an integrated dual-drive dual-parallel Mach-Zehnder modulator (DP-MZM) is proposed. The MZM on the up path of the DP-MZM is used to generate SSB modulation signal, while the MZM on the bottom path of the DP-MZM is unmodulated. By adjusting the amplitude and phase of the unmodulated optical carrier, two optical carriers are cancelled out, which improves the performance of the system with reduced local oscillator (LO) power and large suppression of mixing spurious sidebands. The frequency down-conversion approach is theoretically analyzed and verified by simulation. Simulation results show that the power of frequency down-conversion signal is at least 39 dB higher than that of the mixing spurious sidebands. Besides, 9.5 dB gain, 2.8 dB noise figure (NF) and 1.9 dB spurious-free dynamic range (SFDR) improvements can be obtained compared with the previous OCS modulation frequency down-conversion scheme while the required LO power is 10 dB, 5 dB and 5 dB lower than that of the OCS modulation scheme, respectively.

Millimeter-wave band optical single-sideband modulator using array-antenna-electrode and polarization-reversed structures with asymmetric Mach–Zehnder waveguide

The radio-over-fiber (RoF) technology is effective in millimeter-wave (MMW) wireless systems for future broadband massive mobile communication. In constructing MMW RoF systems, a device for converting MMW signals into lightwave signals is important. In particular, a conversion device for optical single-sideband (SSB) modulation is rather attractive since the signal fading caused by the chromatic dispersion effect of an optical fiber does not occur. We have proposed a new optical SSB modulator using array-antenna-electrode and polarization-reversed structures with an asymmetric Mach–Zehnder waveguide for MMW band RoF systems. By introducing polarization-reversed structures in electro-optic modulators, it is possible to control the optical modulation phase arbitrarily. Therefore, by combining with an asymmetric Mach–Zehnder waveguide, we can obtain the SSB optical modulation in the MMW band without an external power supply. In the experiment, SSB modulation characteristics and the switching of enhanced sidebands were successfully demonstrated in the 60 GHz band.

Digital chromatic dispersion pre-management for SSB modulation direct-detection optical transmission systems

Recently, single-side-band (SSB) modulation direct detection (DD) based optical transmission systems have attracted great interest due to their capability of electronic chromatic dispersion (CD) compensation. In this paper, we investigate the digital chromatic dispersion pre-management for optical SSB signals which are generated by radio frequency (RF) tone based on I/Q modulator and optical carrier based dual-drive Mach–Zehnder modulator (DDMZM) with DD at the C-band via numerical simulations. The impact of CD, self-phase modulation (SPM) and phase-to-amplitude noise on such a SSB DD optical transmission system with I/Q modulator based virtual carrier assisted, and the DDMZM based optical carrier are investigated. The simulation results have successfully demonstrated the transmission of a 224-Gb/s Nyquist 16-ary quadrature amplitude modulation (16QAM) signal over 75-km standard single mode fiber (SSMF) with bit error rate (BER) less than 3.8 × 10−3 in a SSB-DD system by using digital CD pre-management. It is shown that the SPM induced impairment can be optically mitigated by the residual positive CD of the SSMF link.

Proposal and performance analysis on the PDM microwave photonic link for the mm-wave signal with hybrid QAM-MPPM-RZ modulation

A polarization division multiplexed (PDM) microwave photonic link for the millimeter (MM)-wave signal with hybrid modulation scheme is proposed in this paper, which is based on the combination of quadrature amplitude modulation, multi-pulse pulse-position modulation and return to zero modulation (QAM-MPPM-RZ). In this scheme, the two orthogonal polarization states enable simultaneous transmission of four data flows, which can provide different services for users according to the data rate requirement. To generate hybrid QAM-MPPM-RZ mm-wave signal, the QAM mm-wave signal is directly modulated by MPPM-RZ signal without using digital signal processing (DSP) devices, which reduces the overhead of the encoding process. Then, the generated QAM-MPPM-RZ mm-wave signal is transmitted in PDM microwave photonic link based on SSB modulation. The sparsity characteristic of QAM-MPPM-RZ not only improves the power efficiency, but also decreases the degradation caused by the fiber chromatic dispersion. The simulation results show that, under the constraint of the same transmitted data rate, the PDM microwave photonic link with 50 GHz QAM-MPPM-RZ mm-wave signal achieves much lower levels of bit-error rate than ordinary 32-QAM. In addition, the increase of laser linewidth brings no additional impact to the proposed scheme.

Optical single sideband modulation with tunable optical carrier-to-sideband ratio using a modulator in a Sagnac loop

We propose and experimentally demonstrate a cost-effective approach to achieve optical single sideband (OSSB) modulation with tunable optical carrier-to-sideband ratio (OCSR) based on a bi-directional use of an OSSB modulator. The key concept of the proposed scheme is to use an OSSB modulator which is incorporated in a Sagnac loop where a light wave is modulated in the form of SSB modulation along the clock-wise direction while the orthogonal light is not modulated along the counter clock-wise direction due to the velocity mismatch. The signals along two directions are combined together at the output of the Sagnac loop via a polarization beam splitter (PBS). Thus a partial orthogonal SSB (PO-SSB) modulated signal is obtained. The generated signal is then sent into a polarization controller (PC) followed by a polarizer. An OSSB-modulated signal with tunable OCSR from −10 to 27dB is achieved by adjusting the PC in the experiment. The proposed scheme is wavelength independent, which can support low microwave bandwidth and achieve flexible wavelength tunability.

An Optical Frequency Shifter Based on High-Order Optical Single-Sideband Modulation and Polarization Multiplexing

We propose and experimentally demonstrate a novel electro-optic frequency shifter with frequency multiplication operation based on high-order optical single-sideband (SSB) modulation and polarization multiplexing using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. By changing the dc bias phases of the modulator and the phase difference between the input RF signals, two-high-order SSB modulation signals are generated from the two QPSK modulators. After that, the two optical signals are polarization multiplexed and then projected to one direction to remove the low-order sidebands while only the high-order sideband is reserved. The scheme is numerically analyzed with the modulation indices of the modulator for optimal operation. A distinct advantage of this approach is the capability to generate a frequency shifting with a continuous and ultrawide tunable range (more than ±100 GHz), and the tuning operation is accurate, simple, and flexible. An experiment is carried out to achieve a frequency-doubled optical frequency shifter. A continuous frequency shifting ranged from −36 to 36 GHz is experimentally verified.

Broadband and tunable RF photonic phase shifter based on optical SSB modulation and FBG filtering

A broadband RF photonic phase shifter that can achieve the tunable phase shift with little RF power variation is presented. It is based on homodyne mixing technique. The beating between phase-modulated optical carrier and the first-order sideband can generate RF signal with desired phase shift. Results show the RF phase shifter can achieve a continuous 0–360° phase shift with low power variation at the frequency above 21.5GHz.

Optical Vector Network Analyzer Based on Single-Sideband Modulation and Segmental Measurement

We propose an optical vector network analyzer (OVNA) based on single-sideband (SSB) modulation and segmental measurement. The motivation of this work lies in the fact that it is hard for the previous SSB-based OVNA to measure a device-under-test (DUT) with bandpass response. In our scheme, the transmission response of the DUT is divided into several segments, which are measured one by one using the SSB modulation method. The frequency interval between adjacent segments is precisely controlled by a microwave source. The full transmission response of the DUT is obtained by combining the measured results of different segments. The adjacent segments are connected using the overlapped transmission responses. A proof-of-concept experiment was carried out to measure the transmission response of an optical bandpass filter. It was successfully obtained over a frequency range of 80.05 GHz with a resolution of 25 MHz.

The Implemention of a Digital SSB Modulator Based on Folding Transformation

Single-Sideband (SSB) modulation is now widely used for its high band efficiency and low power consumption. In anolog SSB systems, it is usually hard to achieve high performance due to many nonideal factors of anolog components and circuits, such as the I/Q channel mismatch and temperature drift. To overcome these disadvantages, a digtal SSB modulation system based on the Weaver method is designed in this paper. In this system we creatively use the onchip ADC of the ARM processor for audio sampling. Besides, the CORDIC algorithm and the folding transformation are also utilized to reduce hardware costs in the FPGA implemention. This paper mainly discusses the theory and implemention of the Weaver SSB modulation system, and shows the experimental results on actual hardware.

Application of phase-shifted fiber Bragg grating in single sideband transmission–based radio-over-fiber system

We propose a prototype for single-sideband (SSB) transmission based radio-over-fiber system by employing a phase-shifted fiber Bragg grating. The grating has different transmission spectrum characteristics with different phase-shift magnitudes. Then, it is used in a millimeter-wave (mm-wave) SSB modulation scheme. In the scheme, only one PS-FBG is used to realize the following functions: first, the conversion from optical dual-sideband to optical single-sideband with carrier reduction modulation can be easily achieved and second, the optical carrier-to-sideband ratio (OCSR) can be eliminated completely. In our work, the OCSR can be reduced from 33.95 dB to the optimum 0 dB and a 60 GHz mm-wave can be detected after photodiode.

Electro‐optic SSB modulator with 90° hybrid directly prepared onto LiNbO 3 substrate

Optical single-sideband (SSB) modulation is theoretically realised by applying two modulation signals with a 90° phase difference to the dual-electrode type electro-optic (EO) modulator. A branch-line coupler (BC) as the microwave 90° hybrid was directly prepared on the EO modulator substrate, LiNbO 3 , to create two modulation signals from a single input signal. Output ports of the BC were connected to the modulation electrodes on the substrate. Thereby, an EO optical SSB modulator was realised with a single-tip and a small-sized configuration. The SSB modulator was designed and fabricated for around 10 GHz modulation frequency and 1550 nm light wavelength. The optical SSB modulation operation with a sideband suppression ratio of more than 20 dB was confirmed by the experiment.

High-Spectral-Efficiency Photonic Frequency Down-Conversion Using Optical Frequency Comb and SSB Modulation

A high-spectral-efficiency photonic frequency down-conversion approach for wavelength-division-multiplexing radio-over-fiber (WDM-ROF) uplinks is proposed and experimentally investigated. In the approach, an optical frequency comb serves as the carriers of multiple channels, and each comb line is modulated by the upstream radio-frequency (RF) signal via single-sideband modulation. At the central station, the beating between the sideband with upstream signal and its adjacent optical carrier leads to photonic frequency down-conversion without additional optical frequency shifts. Due to the band overlapping or the reduction of guard band between adjacent channels, a high spectral efficiency is achieved for WDM-ROF uplinks. A two-channel experimental uplink is established, where a 15-GHz RF signal carrying quadrature phase shift keying (QPSK) data is successfully down-converted to a 2-GHz intermediate frequency (IF) signal. For the 10-Mb/s QPSK data, the measured eye diagrams and the constellation diagrams clearly show the effectiveness of the frequency down-conversion and the influence of the transmission distance. In fact, the proposed approach is applied to the down-conversion at a high data rate up to several gigabits per second, such as a simulation demonstration at 2.5 Gb/s.

Single-sideband modulated radio-over-fiber system based on long period fiber grating

We present a prototype for optical single-sideband (SSB) modulated radio-over-fiber (RoF) system by employing a long period fiber grating (LPFG). A LPFG with 13.78nm base width of transmission spectrum and 0⿿23.2dB of transmission depth was designed by using commercial software. Then it is used in RoF SSB modulation scheme. In the scheme, a Mach⿿Zehnder modulator modulates the light wave with millimeter-wave driving signals to realize optical double-sideband (ODSB) modulation, the generated ODSB modulation signals pass through a LPFG. Due to the negative slope in transmission spectrum, the lower sideband experiences higher attenuation than the upper sideband. Thus the conversion from ODSB to optical single sideband with carrier (OSSB+C) can be easily achieved by using only one LPFG. Also, the carrier to sideband ratio (CSR) can be reduced by using a LPFG, results show the CSR can be decreased from 12.49dB to 1.1dB.

Theoretical and Experimental Study on Improved Frequency-Locked Multicarrier Generation by Using Recirculating Loop Based on Multifrequency Shifting Single-Sideband Modulation

We propose and experimentally demonstrate a novel scheme to generate optical frequency-locked multicarrier by using a recirculation frequency shifter (RFS) loop based on multifrequency shifting single-sideband (MFS-SSB) modulation with improved tone-to-noise ratio (TNR) performance. Theoretical study shows that we can generate N subcarriers for each round trip without interference by using MFS-SSB, and the recirculation times are reduced to 1/N of the regular scheme based on single-frequency shifting single-sideband (SFS-SSB) modulation. Finally, the double-frequency shifting SSB modulation is carried out for demonstration in our experiments with a double-carrier source from double ECLs and single ECL with carrier suppression. Using this scheme, we successfully generate more than 95 frequency-locked subcarriers with 15-GHz frequency spacing and TNR larger than 25.3 dB and 23.3 dB, respectively. Compared with the results of a regular SFS-SSB scheme, more subcarriers with improved TNR (10 dB and 8 dB for the 95th subcarrier) are obtained.

Multi-channel multi-carrier generation using multi-wavelength frequency shifting recirculating loop

We propose and experimentally demonstrate a novel scheme to generate optical frequency-locked multi-channel multi-carriers (MCMC), using a recirculating frequency shifter (RFS) loop based on multi-wavelength frequency shifting single side band (MWFS-SSB) modulation. In this scheme, optical subcarriers with multiple wavelengths can be generated each round. Furthermore, the generated MCMC are frequency- and phase-locked within each channel, and therefore can be effectively used for WDM superchannel. Dual-wavelength frequency shifting SSB modulation is carried out with dual-wavelength optical seed source in our experimental demonstration. Using this scheme, we successfully generate dual-channel multi-carriers, and one channel has 28 subcarriers while the other has 29 ones with 25-GHz subcarrier spacing. We also experimentally demonstrate that this kind of source can be used to carry 50-Gb/s optical polarization-division-multiplexing quadrature phase shift keying (PDM-QPSK) signal.

Improved Multicarriers Generation by Using Multifrequency Shifting Recirculating Loop

We propose and experimentally demonstrate a novel scheme to generate optical frequency-locked multicarriers, by using recirculating frequency shifter loop based on multifrequency shifting single-sideband (MFS-SSB) modulation with improved tone to noise ratio (TNR) performance. By using MFS-SSB modulation, we can generate N subcarriers during each round trip without interference, and the recirculation times are reduced to 1/N of the regular scheme based on single-frequency shifting SSB modulation (SFS-SSB). Finally, the double-frequency shifting SSB modulation is carried out for demonstration in our experiment with a double-carriers source. Using this scheme, we successfully generate 95 frequency-locked subcarriers with 15 GHz frequency spacing covering from 1553.81 to 1565.26 nm with TNR larger than 23.3 dB. Compared with the results of the regular SFS-SSB scheme, more subcarriers with improved TNR (8 dB for the 95th subcarrier) are obtained.

The optimization design of tilt-Spectral fiber Bragg grating and its application in SSB modulation based Radio over Fiber system

Based on theoretical analysis and simulation software, the paper researched the performance of transmission after using tilt-Spectral fiber Bragg grating for SSB modulation in Radio over Fiber system. The study concluded that DSB signal can be converted to SSB signal by using tilt-Spectral fiber Bragg grating, and inhibit the carrier power. There are two ideal conditions for a best grating. First, one side of DSB signal will be completely filtered, while the other side remains the same power. Secondly, carrier power equals to sideband power in SSB signal, which means that carrier-to-sideband ratio is 0dB. As the result, the best tilt-Spectral fiber Bragg grating is designed. Transmitting the SSB signal which is filtered by the best grating in optical fiber not only eliminates the phenomenon that output amplitude change with the transmission distance cyclically, it also enhances the transmission efficiency and receiver sensitivity.

A novel optical SSB modulation scheme with interfering harmonics suppressed for ROF transmission link

A novel optical SSB modulation scheme for ROF transmission link is proposed in this paper, the scheme employs two parallel MZMs to generate an SSB signal with major high-order interfering harmonics well suppressed. The SSB signal generated by conventional modulation scheme is interfered by adjacent high-order harmonics, and such interference may cause distortion on the RF signal generated at the base station (BS). As major high-order interfering harmonics are well suppressed in the proposed scheme, the power of the generated RF signal can be avoided and the transmission performance of the ROF transmission link is largely improved.

Theoretical and experimental investigation of compatible SSB modulation for single channel long-distance optical OFDM transmission

We present the first experimental demonstration of compatible single-sideband (compatible-SSB) modulated OFDM optical system at 11.1Gb/s data rate for long distance transmission over 675 km uncompensated standard single-mode fiber. Compatible-SSB modulation employing a simple dual-drive Mach-Zehnder modulator (MZM) in the transmitter and direct-detection at the receiver provides an OFDM system implementation with reduced complexity. It does not require a guard-band between the carrier and the OFDM sideband and so makes full use of available digital-to-analog converter (DAC) bandwidth. We demonstrate digital pre-compensation applied in the transmitter to correct MZM nonlinear transfer function and to improve the system transmission performance. We show that optimum modulation index value decreases with increasing transmission distance. We have also investigated the impact of self-phase modulation (SPM) on the system performance, and show that a compatible-SSB modulated system is less vulnerable to SPM in comparison to the conventional offset-SSB modulation at the same data rate.