Carrier Suppression Modulation Research Articles

Phase noise characteristics of the carrier transmitted by the double-sideband–carrier-suppressed modulation system

Phase noise characteristics of the carrier transmitted by the double-sideband-carrier-suppressed (DSB-CS) modulation system are investigated. On the basis of the established DSB-CS modulation system, the phase noise of the input carrier and the output doubled frequency carrier is measured. The influencing factors on the far-from-carrier phase noise are discussed in detail. The noise current mean-square value of the signal-spontaneous beat noise is first derived in the case that there are two first-order optical sidebands generated by DSB-CS modulation. It is shown that the far-from-carrier phase noise is degraded primarily due to the signal-spontaneous beat noise and the relative-intensity noise.

Simple distributed optical fiber sensor based on Brillouin amplification of microwave photonic signals

A simple distributed fiber sensor is proposed by Brillouin amplification and depletion of microwave photonic signals. This technique utilizes optical carrier suppression (OCS) modulation to generate two sidebands acting as the pump waves. After Fresnel reflection at the cleaved end of the fiber under test (FUT), the pump waves are converted to probe waves. By sweeping the modulated microwave frequency, the stimulated Brillouin scattering (SBS) spectra and Brillouin frequency shift (BFS) can be precisely characterized. As a result, the accurate measurement of the Brillouin frequency shift makes good determination of the distributed temperature or stain along the FUT, and the position along the FUT can be resolved and controlled by the delay of the microwave pulses. Furthermore, our proposed sensing system is implemented with a single-ended configuration which has shown many advantages such as immunity of the laser frequency fluctuation and compact setup without additional pump laser source and filters.

Scheme for a High-Capacity 60 GHz Radio-Over-Fiber Transmission System

We investigate a scheme for a 60 GHz radio-over-fiber transmission system by using a dual-electrical Mach–Zehnder modulator (De-MZM) and an optical interleaver. Such a system includes the generation of 60 GHz millimeter-wave (mm-wave) signals and the delivery of a remote local oscillator (LO). In the scheme, two lasers with frequency deviation are used as sources, and a De-MZM is biased at the minimum transmission point to realize optical carrier suppression modulation. After fiber transmission, an optical interleaver is used to separate subcarriers. If one laser is modulated with baseband data and the other is not, 60 GHz mm-wave signals with and without modulating data can be generated by using photodiodes, one of which can be used in mm-wave communication and the other can be used as a remote LO. In this work, we theoretically analyze the bit-error-rate performance and power degradation due to the lasers’ phase noise. Our scheme uses only a commercially used De-MZM and optical interleaver; therefore, no sensitive equipment and complicated structure is needed, which guarantees the system has steady performance and a cost-effective architecture.

Simultaneous wired and wireless link for orthogonal frequency-division multiplexing wavelength-division-multiplexed passive optical network compatible with radio-over-fiber system

Simultaneous wired and wireless link services in a novel optical line terminal for orthogonal frequency-division multiplexing (OFDM)-wavelength-division-multiplexed passive optical network compatible with radio-over-fiber system is proposed and experimentally demonstrated. In the optical line terminal, optical carrier suppression modulation scheme is used to generate a 40-GHz optical millimeter-wave (mm-wave). 2.5-Gb/s OFDM signal is carried by the 40-GHz optical mm-wave. In the base station, we can provide simultaneous wired and wireless services. The downstream OFDM lightwave can be reused to carry 2.5-Gb/s on-off Keying nonreturn-to-zero (OOK-NRZ) upstream data without erasure of the downstream data.

RoF downlink transmission system using FWM effect of SOA for generating MM-Wave

We propose a millimeter wave radio-over-fiber system to provide downlink service by using four-wave-mixing effect in semiconductor optical amplifier for millimeter-wave generation. At the central station, microwave source is 5.4-GHz. The optical carrier suppression modulation scheme and semiconductor optical amplifier are employed to simultaneously generate 32.4-GHz (sextuple fundamental) optical millimeter wave and up-convert data signal. At the base station, the downstream is received by a high-speed photodiode and base data are recovered by an electrical mixer. Theoretic analysis and experimental results show that the downlink 2.5-Gb/s data is successfully transmitted over 20-km single mode fiber with less than 0.15-dB power penalty.

High-Spectral-Purity Millimeter-Wave Signal Optical Generation

In this paper, novel approaches for millimeter-wave signal generation using double-sideband suppressed-carrier modulation and four-wave mixing are proposed and demonstrated. The millimeter-wave signal is generated at a photodetector by beating the optical sidebands, which are gained from intensity modulation and after semiconductor optical amplifiers. In the proposed methods, the generated millimeter-wave signal has a frequency that is double, quadruple, sextuple, 12 times, or even 18 times higher than the microwave drive signal. And, it has quite good gain flatness with extremely high-spectral-purity and stability. The phase noise performance of the generated millimeter wave is investigated. The 3-dB linewidth of the millimeter wave has no broadening after propagating through 20-km standard single-mode fiber.

Investigation of high-speed optical FSK generation scheme based on carrier suppression and phase modulation

We propose and numerically investigate a novel high-speed (40-Gb/s and above) optical frequency shift-keying (FSK) transmitter scheme. By optical carrier-suppressed modulation and differential phase-shift-keying (DPSK) to intensity modulation (IM) conversion, only one light source is needed in the proposed scheme to generate high-speed optical FSK signals. By using a Mach–Zehnder modulator (MZM) as phase modulator and an additional delay interferometer (DI) cascaded after the carrier-suppressed MZM to suppress the remaining carrier, the performance of our scheme can compete with the double-light-source counterparts. The transmission performances of the FSK signal generated with the proposed scheme as well as detuning and bandwidth tolerance of the demodulation filter are also carefully investigated. Simulation results show that the proposed FSK generation scheme is very suitable for the next-generation optical access network and optical label switching network. A potential application of our scheme in high-speed passive optical network is proposed.

Long Range and cm-Level Spatial Resolution Measurement Using Coherent Optical Frequency Domain Reflectometry With SSB-SC Modulator and Narrow Linewidth Fiber Laser

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper describes coherent optical frequency domain reflectometry (C-OFDR) with cm-level spatial resolution over 5 km. We propose the use of a single sideband with a suppressed carrier (SSB-SC) modulator and a narrow linewidth fiber laser as a tunable light source for C-OFDR. The advantage of using SSB-SC modulation is clarified theoretically by comparison with a double sideband with suppressed carrier modulation. We achieved cm-level spatial resolution over a 5-km measurement range and high sensitivity with a noise level 30 dB lower than the Rayleigh backscattering level. </para>

Study of a novel high-speed all-optical orthogonal modulation scheme based on frequency-shift keying and intensity-modulated labeling

We propose and demonstrate a novel orthogonal optical la- beling scheme based on 40-Gbit/s optical frequency-shift keying FSK payload and 2.5-Gbit/s intensity-modulated IM labeling. Using the technology of carrier-suppressed modulation and conversion of differen- tial phase-shift keying to IM, only one light source is needed to generate the optical FSK signal. The system performance, including range of IM modulation depth, bit error ratio, and dispersion limitation, is carefully investigated by numerical simulation. With IM modulation depth of 0.4, the 40 Gbit/s FSK payload and 2.5-Gb/s IM label are transmitted over a 50-km standard single mode fiber SMF with 0.87 and 0.92 dB penalty and show immunity to input power range upto 11 and 15 dB, respec- tively. Optimal methods to improve the system performance are also proposed and discussed. After optimization, the IM modulation depth can be reduced to 0.2. © 2008 Society of Photo-Optical Instrumentation

Impact of Nonlinear Transfer Function and Imperfect Splitting Ratio of MZM on Optical Up-Conversion Employing Double Sideband With Carrier Suppression Modulation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <?Pub Dtl=""?>Generation of optical millimeter-wave (mm-wave) signal using a Mach–Zehnder modulator (MZM) based on double-sideband (DSB), single-sideband (SSB), and double-sideband with carrier suppression (DSBCS) modulation schemes have been demonstrated for various applications, such as broadband wireless signals or optical up-conversion for wavelength-division-multiplexing (WDM) radio-over-fiber (RoF) network, wideband surveillance, spread spectrum, and software-defined radio. Among these schemes, DSBCS modulation offers the best receiver sensitivity, lowest spectral occupancy, the least stringent requirement of electrical bandwidth, and the smallest receiving power penalty after long transmission distance. Nonetheless, the inherent nonlinear E/O (electrical/optical) conversion response of a MZM is such that the signal quality of the optical mm-wave suffers. Fabrication tolerances make a balanced 50/50 splitting ratio of the MZM's y-splitter particularly difficult to achieve. As a result, imbalanced MZMs have a finite extinction ratio (ER) and degrade the optical carrier suppression ratio (OCSR) using DSBCS modulation. In this paper, the effect of the MZM nonlinearity and imbalanced y-splitter on optical mm-wave generation by DSBCS modulation is theoretically and experimentally investigated. A novel approach with better performance and greater cost-effectiveness than dual-electrode MZM (DD-MZM) is presented to realize a DSBCS modulation scheme based on a single-electrode MZM (SD-MZM). </para>

Instantaneous Visualization of K-Band Electric Near-Fields by a Live Electrooptic Imaging System Based on Double Sideband Suppressed Carrier Modulation

This paper discusses instantaneous electric near-field imaging in the K-band. The imaging technique is based on the live electrooptic imaging (LEI) scheme, which was originally developed for electric near-field imaging in the microwave range. The measurement frequency of the LEI system is extended by using the second-order harmonic component of modulated light as a photonic local oscillator signal. We demonstrated electric near-field imaging over rather ordinary components such as an SMA connector and a microstrip transmission line at frequencies up to 25 GHz.

A Novel Direct Detection Microwave Photonic Vector Modulation Scheme for Radio-Over-Fiber System

This letter demonstrates the feasibility of a novel direct detection microwave photonic vector modulation scheme for the radio-over-fiber (RoF) system. Unlike the traditional double-sideband with optical carrier suppression modulation scheme, which can carry only the on-off keying data format, the proposed scheme encodes the electrical vector signal on either the upper sideband (USB) or the lower sideband (LSB) only and a pure optical subcarrier on the other sideband. Therefore, phase and amplitude information will be preserved after direct detection. A frequency doubling scheme is employed to reduce the cost of RoF systems. Additionally, the relative intensity between USB and LSB can be easily tuned by adjusting the individual power of electrical driving signals to optimize the performance of the optical radio-frequency signals. A proof-of-concept experiment is conducted by using a 1.25 Gb/s BPSK signal at a carrier frequency of 20 GHz. After transmission over 50-km single-mode fiber, the receiver sensitivity penalty is less than 0.5 dB.

Frequency sixupler for millimeter-wave over fiber systems

In this work, we propose and investigate a novel technique for the generation of millimeter-wave (mm-wave), i.e. frequency sixuplexing technique. The proposed technique is comprised of two cascaded Mach- Zehnder modulators (MZMs). The first MZM, biased at maximum transmission, is only used for even-order optical harmonic generation, and then a second MZM, biased at minimum transmission, is used for both optical carrier suppression modulation and data signal modulation. As an example, we consider an RF at 10 GHz, which carries the data signal and drives the MZMs; and an mm-wave signal at 60 GHz, i.e. a frequency sixupler, is obtained. It is found that our proposed sixupler leads to an 8-dB higher RF power at 60 GHz and a 6-dB improvement in receiver sensitivity with comparison to the conventional technique, i.e. optical carrier suppression modulation. The generated mm-wave signal is robust to fiber chromatic dispersion. The proposed technique is verified by experiments.

Crosstalk Suppression of a Balanced Bridge Interferometric-Type LiNbO$_{3}$ Optical Switch by Using Mach–Zehnder Structures

Crosstalk in a balanced bridge interferometric-type optical switch is highly suppressed by using Mach-Zehnder (MZ) structures as intensity trimmers. An imbalance in optical power is caused by deviations from the ideal dividing ratio of directional couplers in the switch, which causes an increase in the crosstalk. This imbalance was compensated for by adjusting the transmittances of the nested MZ structures. A crosstalk of less than 55 dB has been achieved even for alternating voltage signals. It is also shown that the crosstalk reduction is possible for a control voltage signal of more than 10 GHz, which is based on double-sideband suppressed-carrier modulation spectra measurement results.

Photonic method for ultra-wideband monocycle pulse frequency upconversion

A novel optical method for frequency upconversion in ultra-wideband (UWB) system application is proposed and demonstrated. A UWB monocycle pulse can be generated by cross-polarsation modulation combined with carrier-suppressed modulation, and after an O/E detector, it can be converted to 32 GHz band. After electrical downconversion, the UWB monocycle pulse has a fractional bandwidth of 144% and fits UWB applications.

A Radio-Over-Fiber Downstream Link Employing Carrier-Suppressed Modulation Scheme to Regenerate and Transmit Vector Signals

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this letter, the optical carrier-suppressed (OCS) modulation scheme is employed to transmit vector signals in radio-over-fiber systems. The proposed architecture employing the OCS modulation scheme needs only a balanced single driven Mach–Zehnder optical modulator, and has advantages of dispersion immunity and doubled frequency. Both detailed theoretical analysis and experiments are presented to demonstrate the feasibility of the proposed architecture. </para>

A Photonic Microwave Frequency Quadrupler Using Two Cascaded Intensity Modulators With Repetitious Optical Carrier Suppression

We theoretically analyzed and experimentally demonstrated a novel 4- to 40-GHz frequency quadrupler for radio-over- fiber systems. By using an optical carrier suppression modulation scheme in two cascaded intensity modulators, four-fold microwave or millimeter wave signals are optically generated without the need for an optical and electrical notch filter to remove the residual carrier components. Moreover, the limitation of high drive voltage is greatly reduced through tandem intensity modulation with pi/2 phase shift between two driving signals.

Bidirectional ROF Links Using Optically Up-Converted DPSK for Downstream and Remodulated OOK for Upstream

We propose a novel radio-over-fiber system to provide full-duplex services by using optical differential phase-shift keying modulation format at the central station for downstream and on-off keying remodulation of the downlink carrier at the base station (BS) for upstream. The optical carrier suppression modulation scheme is employed to simultaneously generate and up-convert 40-GHz optical millimeter wave. As the same optical carrier is used for both uplink and downlink, no additional light source is required at the BS, which greatly reduces the cost and simplifies the overall system. Simulations and experimental results show that the bidirectional 2.5-Gb/s data is successfully transmitted over 40-km single-mode fiber (SMF-28) with less than 2-dB power penalty

A Novel Radio-Over-Fiber System With Wavelength Reuse for Upstream Data Connection

We have experimentally demonstrated a novel wavelength reuse scheme for up-link connection in a radio-over-fiber (ROF) system. The dual-mode lightwave generated by optical carrier suppression modulation is separated by an optical interleaver. One of the dual-mode lightwaves is modulated with a baseband data at 2.5 Gb/s. The other lightwave will be used for the optical carrier for the up-link data modulation. There is no additional laser source for the upstream data generation in the base station. By this method, we simplify the configuration of the ROF system and reduce the cost of the system

Frequency upconversion of multiple RF signals using optical carrier suppression for radio over fiber downlinks

We propose and analyze a technique of an optical carrier transmitting two RF signals using optical carrier suppression. A single optical Mach-Zehnder modulator is used for both optical carrier suppression and signal modulation, and optical carrier suppression modulation is also used for frequency conversion of RF signals. This work shows that in contrary to the case of an optical carrier transmitting a single RF signal with optical carrier suppression where stronger optical carrier suppression improves the upconverted RF signal, weaker optical carrier suppression is preferred for an optical carrier transmitting two RF signals due to nonlinear distortion because the nonlinear distortion is reduced by using weaker optical carrier suppression. We find that the usable range of optical carrier suppression ratio is from 10 to 18 dB for RF signal upconverted to 20 GHz and beyond, and the best optical carrier suppression ratio is around 10 dB. We verify the concept and analysis with experiment. In experiment, we used two RFs at 6 and 18 GHz transmitting two 750 Mb/s signals. The experiment for the first time demonstrated that an optical carrier can transmit two RF signals using optical carrier suppression and showed that upconverted RF signals are degraded by nonlinear distortion, particularly for upconverted RF signal at 12 GHz, i.e. the RF signal at the lower frequency.