Optical Single Sideband Modulation Research Articles

Optical single-sideband modulator for broad-band subcarrier multiplexing systems

We experimentally demonstrate an enhanced optical single-sideband (OSSB) modulator for subcarrier-multiplexing (SCM) systems that provides improvement of the output optical modulation depth without increasing either the second-order or the third-order nonlinear distortion of the transmitted radio frequency signal. The modulator is deployed in an SCM link conveying 4 /spl times/ 622-Mb/s modulated subcarriers, demonstrating an enhancement of five orders of magnitude in bit error rate compared to the use of a dual-electrode OSSB modulator design. In addition, the dispersion penalty for the worst-case channel is reduced to less than 1.7 dB.

Noiseless amplification and signal-to-noise ratio in single-sideband transmission.

We study the properties of optical single-sideband (SSB) modulation with respect to signal-to-noise ratio and limits to spectral efficiency. We show that SSB signals undergo truly noiseless amplification, which can be understood in view of Heisenberg's uncertainty principle. Yet, contrary to previously published results, this phenomenon offers no advantages in terms of the signal-to-noise ratio of the amplified signal. We show that, when an intensity receiver is used, single-sideband modulation can improve spectral efficiency in the limit of a high optical signal-to-noise ratio and in the presence of a strong carrier signal.

Eye openings in WDM transmission systems with optical SSB modulation using a Hilbert transformer and with electrical low‐frequency band equalization

AbstractA narrowband optical modulation model was devised based on an optical single sideband (SSB) modulator using a finite‐order Hilbert transformer. The model's wavelength multiplexing transmission characteristics were analyzed by evaluating the eye openings obtained by computer simulation. First, we evaluated a transmission model with no adjacent channels and found that the transmission eye openings after demodulation were degraded by the characteristics of the optical SSB modulation and the frequency response of a channel separation filter. The degradation of the eye openings could clearly be corrected by applying electrical attenuation equalization in the low‐frequency band after baseband demodulation. Next, we evaluated the eye openings obtained by the optimum channel separation filter determined as a function of the order of the Hilbert transformer by evaluating the transmission model extended to three‐channel multiplexing that includes adjacent channels. It was found that applying electrical attenuation equalization improved the received signal characteristics as the order of the Hilbert transformer increased. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 1–11, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10058

Wavelength-interleaved OADMS incorporating optimized multiple phase-shifted fbgs for fiber-radio systems

We demonstrate that a single fiber Bragg grating (FBG)-based optical add-drop multiplexer can be used to improve the optical spectral efficiency in a mm-wave WDM-fiber wireless network. The technique employs wavelength interleaving in conjunction with optical single-sideband modulation, together with a single multiphase-shifted fiber Bragg grating. Wavelength optical add-drop features are also demonstrated using the grating, and our results show the performance of the novel grating in terms of channel isolation and add-drop functionality. We perform simulations to optimize placement of the phase shifts when an apodization profile is applied to the grating, in an attempt to minimize in-band and out-of-band transmission-amplitude ripples. Experiments are performed using cascade configurations both with the apodized gratings with optimal phase-shift positions and with the original unoptimized gratings. The experimental results demonstrate how these novel gratings can be used in fiber-radio networks incorporating multiple optical add-drop multiplexers.

Simple optical single-sideband modulator for fibre-radio applications

A simple scheme for optical single-sideband (OSSB) modulation based on the combination of a commercial optical intensity modulator and passive fibre optic components is proposed. In addition to dispersion compensation, this OSSB modulator has experimentally demonstrated enhancement of the optical modulation depth and receiver sensitivity of a Ku-band antenna remoting link.

Numerical Simulation of a lightwave synthesized frequency sweeper incorporating an optical SSB Modulator composed of four optical phase Modulators

We describe the numerical analysis of a lightwave synthesized frequency sweeper (LSFS) that uses an optical single-sideband (SSB) modulator composed of four optical phase modulators. The SSB modulator realizes a large frequency shift in the LSFS. This means that we can reduce the number of pulse circulations in the LSFS cavity to cover a given frequency sweep range. We propose a frequency-domain analysis method for the LSFS, in which a general optical modulator is expressed by using a matrix that includes optical phase terms. We employ this method to simulate the LSFS for several different phaseand group-velocity dispersion values in the lightpaths in the LSFS cavity. The results indicate that we can realize a linear frequency sweep by adjusting the phase change of the modulation signal during the cavity round-trip time.

Using optical single sideband modulation technique to improve CATV system performance

We propose and demonstrate an externally modulated AM-vestigial sideband (VSB) CATV erbium- doped fiber amplifier-repeated system which uses an optical single sideband modulation technique to improve the composite second order (CSO) and composite triple beat (CTB) performances in systems. In comparison with conventional externally modulated fiber optical CATV systems, excellent performances of carrier-to-noise ratio >50 dB, CSO?72 dB, and CTB?69 dB were achieved for the full channel band over a 100-km single-mode fiber transport.

Multiple output photonic RF phase shifter using a novel polymer technology

Photonic RF phase shifters with independent multiple outputs have been fabricated using our novel polymer modulator technology. These integrated planar devices incorporated low crosstalk optical waveguide crossings, which were critical to the independent operation of RF phase outputs. The measured RF phase shift characteristics at 20 GHz were approximately linear up to /spl sim/150/spl deg/ with respect to do control voltages. In addition, the optical single-sideband (SSB) modulators, which were part of the phase shifters, were characterized and SSB modulation was confirmed.

Subcarrier multiplexing for high-speed optical transmission

The performance of high-speed digital fiber-optic transmission using subcarrier multiplexing (SCM) is investigated both analytically and numerically. In order to reduce the impact of fiber chromatic dispersion and increase bandwidth efficiency, optical single-sideband (OSSB) modulation was used. Because frequency spacing between adjacent subcarriers can be much narrower than in a conventional DWDM system, nonlinear crosstalk must be considered. Although chromatic dispersion is not a limiting factor in SCM systems because the data rate at each subcarrier is low, polarization mode dispersion (PMD) has a big impact on the system performance if radiofrequency (RE) phase detection is used in the receiver. In order to optimize the system performance, tradeoffs must be made between data rate per subcarrier, levels of modulation, channel spacing between subcarriers, optical power, and modulation indexes. A 10-Gb/s SCM test bed has been set up in which 4 /spl times/ 2.5 Gb/s data streams are combined into one wavelength that occupies a 20-GHz optical bandwidth. OSSB modulation is used in the experiment. The measured results agree well with the analytical prediction.

Improved sideband suppression of optical SSB modulation using all-optical Hilbert transformer

A novel optical single-sideband (SSB) modulation system using an all-optical Hilbert transformer is proposed. The sideband suppression characteristics are analysed and compared with a conventional system using an electrical transformer. The side-lobe to main-lobe peak suppression ratio exceeding 40 to 60 dB is shown, significantly outperforming the conventional system.

Technique for increasing optical spectral efficiencyin millimetre-waveWDM fibre-radio

A novel technique for increasing the spectral efficiency of millimetre-wave fibre-radio systems by employing wavelength interleaving in conjunction with optical single sideband modulation, is proposed and demonstrated. The technique has been demonstrated experimentally by employing a wavelength interleaved optical add-drop multiplexer and transmission of a 155 Mbit/s BPSK signal at 36 GHz over 20 km of fibre.

Single side-band modulation performance of a LiNbO3 integrated modulator consisting of four-phase modulator waveguides

Single side-band (SSB) technologies are especially useful in optical fiber communication systems, such as higher density wavelength multiplexing and long-haul fiber transmission due to less nonlinear optical effects, because of the reduced optical power. This letter reports on the SSB modulation performance of a LiNbO/sub 3/ integrated modulator consisting of four phase modulator waveguides. Optical SSB modulation with suppressions of main carrier (-22.6 dB) and J/sub 3/ subcarrier (-18.4 dB) of a 10-GHz single-tone signal with a driving voltage of 6.3 V/sub p-p/ was demonstrated. The total insertion loss was 10.6 dB.

A 60-GHz optoelectronic mixing scheme of high image and carrier rejection ratios with an integrated optical single-sideband modulator employed

We report on the first implementation and performance investigation of a 60-GHz-band optoelectronic image rejection mixing scheme based on a broad-band integrated optical single-sideband modulator. We have confirmed a few advantageous features over electrical image rejection mixers, arising from its nature of being free from electrical phase control of millimeter-wave signals. We obtained at the IF frequency of 800 MHz rejection ratios of >40 dB for the image signal and of >20 dB for the local oscillator (LO) signal in the LO frequency range of 55-65 GHz. The LO bandwidth can be extended further. The IF bandwidth with an image rejection ratio of >20 dB was also confirmed to be as broad as 550 MHz, which is limited not by the configuration but by the bandwidth of the 90/spl deg/ hybrid used in this experiment. Furthermore, fiber-optic transmission of a 155.52-Mb/s-DPSK 59.8-GHz optical millimeter-wave signal was successfully demonstrated for a 20-km standard single-mode fiber. A bit error rate of <10/sup -9/ was achieved at the received optical power of -18 dBm with a negligible dispersion penalty.

X-cut lithium niobate optical single-sideband modulator

A hermetically packaged x-cut LiNbO3 optical single-sideband modulator is presented, which successfully performs a carrier-suppression ratio over 25 dB with an RF driving voltage of 8 Vp-p at 10 GHz.

A novel optical label swapping technique using erasable optical single-sideband subcarrier label

To support optical multiprotocol label switching (MPLS) technology in an optical network, we have demonstrated subcarrier label swapping in a 96.2-km, three-node experiment, by using optical single-sideband modulation and an optical notch filter. At each intermediate switching node, an old subcarrier label can be suppressed by 25 dB, while the burst-mode 2.5-Gb/s payload experienced only 2-dB power loss.

Frequency transfer function of dispersive and nonlinear single-mode optical fibers in microwave optical systems

A closed expression of the frequency transfer function nonlinear single-mode optical fibers in microwave optical systems is provided. This expression takes into account both chromatic dispersion and self-phase modulation effects and is valid for optical double-sideband modulation, optical single sideband modulation, and chirped optical transmitters.

Comparison of optical single-sideband modulation and chirped fiber gratings as dispersion mitigating techniques in optical millimeter-wave multichannel systems

A comparative study between optical single-sideband (SSB) modulation and chirped fiber gratings (CFG) as dispersion equalization techniques is carried out. The simulation results show that the dispersion-induced distortion arising in optical millimeter-wave multichannel systems can not be compensated by employing the SSB modulation approach. Furthermore, we have demonstrated that the use of a CFG significantly reduces (nearly 25 dB) the composite triple beat (CTB) distortion. An accurate design of the CFG however must be addressed because the equalized CTB levels are very sensitive to the nonideal characteristics of the CFG such as a deviation of the optimum group delay slope or ripples.

Hybrid harmonic subcarrier optical single sidebandwith phase predistortion

It has been shown that optical single sideband modulation is useful for mitigation of fibre chromatic dispersion effects on subcarrier intensity modulated-direct detection optical links. It is shown that a simple phase compression technique may be employed to reduce the complexity of microwave subcarrier modulated optical links, yielding a general method for phase modulation that is compatible with the inherent argument multiplication encountered in harmonic translation through nonlinear optical networks.

Highly spectrum efficient OFDM/PDM wireless networks by using optical SSB modulation

Optical frequency division multiplexing (OFDM) wireless access network using optical single-sideband modulation is proposed, which allows to deliver different wireless signals from a central station to each base station over an optical fiber network. The optical single-sideband (SSB) OFDM can achieve the highest spectrum efficiency of 0.25 b/s/Hz. A 0.25 b/s/Hz has been experimentally verified by the error-free transport of two-channel 4.98 Gb/s BPSK signal on 10 GHz wireless carrier with the frequency channel interval of 20 GHz at 1550 nm over 50 km-long standard single-mode fiber link. Furthermore, it has been also experimentally confirmed that by introducing the polarization division multiplexing (PDM), the ultimate spectrum efficiency of 0.5 b/s/Hz can be achieved by the hybrid OFDM/PDM.

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.