OSSB Signal Research Articles

CSPR Measurement Method for Optical Single-Sideband Signal

We propose and demonstrate a simple but accurate time-domain method to measure the carrier-to-signal power ratio (CSPR) of optical single-sideband (OSSB) signals. In this method, we estimate the CSPR using the mean and standard deviation of asynchronous amplitude histogram obtained from an oscilloscope equipped with DC-coupled photo-detector. We provide a closed-form expression on the CSPR using these statistical averages. By using numerical simulation, we first assess the validity of our theoretical expression for five different kinds of OSSB signals. Next, we carry out experiments using 100-Gb/s orthogonal frequency-division multiplexed signals to evaluate the accuracy of the proposed method. We show that the proposed method makes the estimation errors less than 0.9 dB over wide ranges of CSPRs and optical signal-to-noise ratios. The accurate CSPR estimation of the proposed method regardless of the frequency gap between the optical carrier and information-bearing signal is also demonstrated.

Improved OSSB modulation with FBG-based acousto-optic tunable filter and Return-to-Zero pulse transmission

Abstract An improved OSSB modulation scheme is proposed in this paper. The improvements are realized by three aspects. Firstly, the fiber Bragg grating based acousto-optic tunable filter (FBG-AOTF) is introduced to tune the Optical Carrier-to-Sideband Ratio (OCSR). Secondly, the Return-to-Zero (RZ) pulse is chosen as the data transmitting pulse. In the end, the OSSB signal with optimized OCSR is separated, and only the optical carrier is modulated by the data. When the transmission distance is within 360 km, the receiving sensitivity of the link in the improved scheme is relatively stable in the range of (−23.6 dBm, −24.1 dBm) with the increase of the distance. While for the original OSSB modulation, under the same condition, the receiving sensitivity is only about −20.0 dBm when the fiber length is 200 km. Not only the OCSR of the OSSB can be optimized, but also the problem of time shift of code edges caused by the fiber dispersion can be eliminated. As a result, both the performance and the stability of the OSSB system can be upgraded in the improved scheme. Two complete simulation systems are built by using the characteristic of the experimentally made FBG-AOTF. And the increased receiving sensitivity of 2.6 dB in the improved scheme further verifies the conclusion.

A Radio over Fiber (RoF) Based Single Sideband Modulated Passive Optical Network (PON) Using Mach Zender Modulator Based on Different Electrical Phase Shifts

Abstract This research work provides an insight on a radio over fiber (RoF) based passive optical network (RoF-PON) utilizing two diverse electrical phase shifts with optical single sideband modulation (OSSB) by exploiting Mach Zender modulator. The influence of chromatic dispersion (CD) in PONs employing single mode fiber (SMF) is a noteworthy issue and should be limited. The two techniques of OSSB modulation, in view of the two distinct angles of the hybrid coupler are employed for the design and implementation of RoF-PON. The RF signal is partitioned into two ways equally before applying it to the dual drive Mach Zender modulator input, utilizing an electrical hybrid coupler that imparts two discrete phase shifts of 90° and 120° to generate two OSSB signals individually. By utilizing traditional OSSB technique having 90° phase shift, either of the first-order sideband (lower or upper first order) suppression occurs yet second-order harmonics are still existent in the system. As opposed to this, the OSSB technique using 120° phase shift causes the suppression of either lower first order and higher second order sideband or vice versa. When contrasted to the PON based on traditional technique (90° phase shift technique), the suppression of second order sideband in PON using 120° technique lessens the system CD. Hence the PON based on 120° phase shift technique has enhanced functionality in terms of system BER, received power and power losses as compared to that with traditional OSSB technique.

Performance optimization of RoF systems using 120° hybrid coupler for OSSB signal against third order intermodulation

The performance of radio over fiber (RoF) system with dual drive Mach Zehender modulator has been optimized against third order intermodulation distortion by using 120° hybrid coupler in transmission system. Signal to Noise Distortion ratio (SNDR) has been evaluated and a performance comparison is also drawn for the systems based on 90° and 120° hybrid coupler in both noise and intermodulation distortion dominant environment. The SNDR is efficiently improved by employing 120° hybrid coupler in noise dominant and intermodulation distortion dominant environment. An improvement of 4.86dB is obtained in the maximum SNDR with 120° hybrid coupler is obtained over at 20km optical fiber length compared with a 90° hybrid coupler based system. A significant reduction of third order intermodulation power at receiver has also been observed with 120° hybrid coupler.

All optical up-converted signal generation with high dispersion tolerance using frequency quadrupling technique for radio over fiber system

A novel all optical up-converted signal generation scheme with optical single-sideband (OSSB) technique for radio over fiber (RoF) application is presented and experimentally demonstrated using low-bandwidth devices. The OSSB signal is generated by one low-bandwidth intensity LiNbO3 Mach-Zehnder modulator (LN-MZM) under frequency quadrupling modulation scheme and one low-bandwidth LN-MZM under double sideband carrier suppressed modulation (DSB-CS) scheme. The proposed all OSSB generation scheme is capable of high tolerance of fiber chromatic dispersion induced power fading (DIPF) effect. Benefiting from this novel OSSB generation scheme, a 26GHz radio frequency (RF) signal up-conversion is realized successfully when one sideband of the optical LO signal is reused as the optical carrier for intermediate frequency (IF) signal modulation. The received vector signal transmission over long distance single-mode fiber (SMF) shows negligible DIPF effect with the error vector magnitude (EVM) of 15.7%rms. In addition, a spurious free dynamic range (SFDR) of the OSSB up-converting system is measured up to 81dBHz2/3. The experiment results indicate that the proposed system may find potential applications in future wireless communication networks, especially in microcellular personal communication system (MPCS).

Optical single-sideband modulation based on silicon-on-insulator coupled-resonator optical waveguides

We propose and demonstrate for the first time an optical single-sideband (OSSB) modulation generation based on silicon-on-insulator coupled-resonator optical waveguides (CROWs) capable of operating at wide bandwidth with enhanced sideband suppression. The optimum order of the CROW filter was synthesized based on comprehensive performance analysis including optical sideband suppression and electrical power variation. Experimental results demonstrate an OSSB signal with sideband suppression as large as 23 dB. The performance of the proposed OSSB was demonstrated via compensating radio frequency (RF) power degradation in the transmission of the RF signal within the fiber.

Orthogonal Single-Sideband Signal Generation Using Improved Sagnac-Loop-Based Modulator

A novel microwave photonics technique that enables the modulation of orthogonal optical single-sideband (OSSB) by using an improved Sagnac-loop-based modulator is proposed and experimentally demonstrated. The dual-driving Mach-Zehnder modulator and polarization-maintaining fiber Bragg grating are integrated inside and outside the Sagnac loop, respectively, in order to realize the OSSB modulation and polarization-selective filtering. Therefore, the precisely defined orthogonal OSSB signal can be generated steadily at 20-GHz carrier frequency in the experiment.

Optical Single-Sideband Modulation Based on a Dual-Drive MZM and a 120° Hybrid Coupler

A novel scheme for implementing high-performance optical single-sideband (OSSB) modulation based on a dual-drive Mach-Zehnder modulator (MZM) and a 120° hybrid coupler is proposed and demonstrated. A RF signal is divided by the 120° hybrid coupler into two parts with equal powers and a phase difference of 120°, and then, led to the two RF ports of the dual-drive MZM. With a proper dc bias, an OSSB signal with the -1st and +2nd-order sidebands (or the +1st and -2nd-order sidebands) suppressed is generated. A numerical simulation and a proof-of-concept experiment are carried out. As compared with the conventional OSSB modulation based on a 90° hybrid coupler, the suppression of the +2nd (or -2nd)-order sideband improves evidently the performance when the OSSB modulation is applied in a radio-over-fiber system or an optical vector network analyzer.

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.

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.

Optical Single-Sideband Modulation Using a Fiber-Bragg-Grating-Based Optical Hilbert Transformer

An all-optical approach to realizing optical single-sideband (OSSB) modulation based on optical Hilbert transform implemented using a fiber Bragg grating (FBG) is proposed and demonstrated. In the proposed approach, an optical double-sideband (ODSB) signal is divided equally into two channels with the output at one channel being the in-phase (I) component and that at the other being the quadrature phase (Q) component. An FBG-based optical Hilbert transformer (HT) is incorporated in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> channel, making the two sidebands out of phase at the output of the HT. The combination of the two optical signals from the two channels leads to the cancellation of one sideband, thus an OSSB signal is generated. An experiment is performed. An OSSB signal with a frequency from 6 to 15 GHz and a sideband suppression ratio (SSR) as large as 20 dB is generated. The transmission of the OSSB signal over a single-mode fiber of 45.6 km is also studied.

Average BER analysis of SCM-based free-space optical systems by considering the effect of IM3 with OSSB signals under turbulence channels

In this paper, we derive the average bit error rate (BER) of subcarrier multiplexing (SCM)-based free space optics (FSO) systems using a dual-drive Mach-Zehnder modulator (DD-MZM) for optical single-sideband (OSSB) signals under atmospheric turbulence channels. In particular, we consider the third-order intermodulation (IM3), a significant performance degradation factor, in the case of high input signal power systems. The derived average BER, as a function of the input signal power and the scintillation index, is employed to determine the optimum number of SCM users upon the designing FSO systems. For instance, when the user number doubles, the input signal power decreases by almost 2 dBm under the log-normal and exponential turbulence channels at a given average BER.

All-optical single-sideband upconversion with an optical interleaver and a semiconductor optical amplifier for radio-over-fiber applications

We propose and experimentally demonstrate an all-optical upconverter for the generation of an optical single-sideband (OSSB) signal in radio-over-fiber (RoF) systems. The OSSB signal, which is required for overcoming the fiber chromatic dispersion problem in RoF systems, is generated by using an all-optical SSB upconverter consisting of an optical interleaver and a semiconductor optical amplifier. With this upconversion technique, OSSB radio frequency (RF) signals with an RF frequency ranging from 15 GHz to 42.5 GHz are generated by mixing an optical intermediate frequency (IF) signal (1 GHz) with an optical local oscillator signal and transmitted over a 46 km standard single-mode fiber. The OSSB RF signal generated by this upconversion technique shows negligible dispersion-induced carrier suppression effects, which are usually observed for an optical double-sideband RF signal. The all-optical SSB upconverter provides high conversion efficiency of up to 29 dB and a sufficiently large spurious free dynamic range of 82 dB.Hz(2/3) for microcellular personal communication system applications.

应用于宽带光载无线通信系统的线性化单边带光信号产生

We propose a new scheme to generate broadband linearized optical single-sideband (OSSB) signal for radio over fiber systems. By using an unbalanced dual parallel Mach-zehnder modulator (DPMZM) followed by optical filtering, a linearized OSSB signal is obtained. With coherent detection, radio frequency (RF) signal can be recovered with simultaneously suppressed second-order distortion and third-order intermodulation. This scheme can be used to realize broadband systems with wide dynamic range.

Improved optical single-sideband generation using the self-modulation birefringence difference in semiconductor optical amplifiers

By employing the self-modulation birefringence difference in a semiconductor optical amplifier (SOA), an improved method is proposed to generate a complete optical single-sideband (OSSB) signal. Over 30 dB sideband suppression ratios (SSRs) of lower OSSB signals are obtained over a 12 dB input power range and a 36 nm wavelength span, with a maximum of over 35 dB. Upper OSSB signals with an SSR of over 15 dB are observed using a SOA for what is believed to be the first time. This method is effective even for the carrier-suppressed signal. The theory for OSSB generation in an SOA is extended and verified by experiment.

Effect of third-order intermodulation on radio-over-fiber systems by a dual-electrode Mach-Zehnder modulator with ODSB and OSSB signals

Third-order intermodulation (IM3) is a very important issue as a degradation factor of system performance in the range of high input signal power. In this paper, the effect of IM3 from a dual-electrode Mach-Zehnder modulator (DEMZM) and a photodetector (PD) is analyzed for optical single-sideband (OSSB) and optical double-sideband (ODSB) signals incorporating fiber dispersion. In addition, the optimum input signal power and the signal-to-noise-and-distortion ratio (SNDR) for the two cases are also investigated to optimize the performance of the entire system. In the case of OSSB signals, the fundamental components are robust against fiber dispersion, whereas their IM3 components are still sensitive to fiber dispersion. Subsequently, the SNDR for OSSB signals fluctuated to within 6 dB in the relatively high input power range due to fiber dispersion. In the case of ODSB signals, both powers of the fundamental and IM3 components are attenuated. However, the power attenuation of IM3 due to fiber dispersion is significantly faster than that of the fundamental. Thus, the SNDR for ODSB signals is improved as fiber dispersion increases until the power of IM3 is greater than that of the additive noise level.

Optical single-sideband transmitter for various electrical signaling formats

A simple high-speed data transmitter to generate optical single-sideband (OSSB) signals using different electrical signaling formats is presented. The OSSB signal is generated by combining the information signal with the Hilbert transform of that signal, obtained by means of electrical processing. A detailed mathematical model is introduced to evaluate the transmitter performance, considering the generation of OSSB signals with different electrical signaling formats. Two signaling formats are evaluated and compared: nonreturn-to-zero (NRZ) and alternate mark inversion. The optimum transmitter operation conditions, namely bias and drive voltages, are derived according to the signaling format used and confirmed experimentally. Transmission tests conducted using 10-Gb/s OSSB-NRZ signals to assess the improvement obtained by electrical dispersion compensation show a significant mitigation of the dispersion distortion.

Hybrid modulator structures for subcarrier and harmonic subcarrier optical single sideband

Optical single-sideband (OSSB) modulation is useful for mitigation of fiber chromatic dispersion effects on intensity modulated-direct detection (IMDD) optical links. We show that hybrid modulator structures based on compatible single-sideband (CSSB) theory serve as general purpose OSSB modulators. We further show that both harmonically upconverted optical double-sideband (ODSB) and harmonically upconverted OSSB signals, generated through the nonlinear characteristics of optical modulators, both provide significant dispersion improvements.