Optical Single-Sideband Modulation at 60 GHz Using Electro-Absorption Modulators

In this paper, we investigate the optical power fluctuation of the output in optical comb generator using an optical single sideband (SSB) modulator with a fiber loop. This fluctuation is caused by undesired sidebands of the SSB modulator. We show that the fluctuation can be suppressed by stabilizing the fiber loop length. In experiment, the averaged peak-to-peak power fluctuation of 23 comb outputs was suppressed from 0.86 dB to 0.13 dB.

We propose and demonstrate an optical single sideband (OSSB) modulation approach with continuously tunable optical carrier-to-sideband ratio (OCSR) theoretically and experimentally. In the proposal, one dual-parallel Mach-Zehnder modulator (DP-MZM) acts as a key component. By properly setting the modulator, three separate sub-modulators inside the DP-MZM can be used to realize the OSSB modulation, optical carrier phase-shift, and lightwave interference. By adjusting the bias voltage of one sub-modulator, the OCSR can be tuned continuously. In the experiment, the tuning range of OCSR is found to be between-20.8 dB and 23.5 dB at modulation index m=0.2. We also analyze the relationship between the OCSR and RF power after detection. It is found that with properly adjusting the OCSR, the receiver sensitivity can be greatly improved.

It is proposed a novel spectroscopy to make a resolution higher with an optical single-sideband (SSB) modulator. It has been experimentally cleared that the system resolution becomes higher order at ~MHz.

An optical single sideband modulator without generating both the −2nd- and +2nd-order sidebands is presented. It is based on a parallel operation of two dual-drive Mach–Zehnder modulators (DDMZMs) where one is operated as a conventional single sideband (SSB) modulator and the other is operated as a single-drive Mach–Zehnder modulator (MZM) biased at the maximum transmission point. The 2nd-order sidebands generated by the SSB modulator and the maximum-biased MZM can be cancelled by controlling the sideband amplitude and phase. Canceling the 2nd-order sidebands eliminates the second-order harmonic component presented at the output of a long-reach fiber optic link. The new SSB modulator can be implemented using standard off-the-shelf components and has a wide bandwidth. Experimental results show >20 dB 2nd-order sidebands suppression for different modulation indexes and 22.6 dB reduction in the fiber optic link output second-order harmonic component, compared to using a conventional SSB modulator formed by a DDMZM and a 90° hybrid coupler. Results also demonstrate that the performance of the new SSB modulator is insensitive to the optical carrier frequency and the input RF signal frequency.

Using a hyperfine blocking filter based on a virtually imaged phased-array as the spectral disperser, we present a novel scheme of optical carrier-suppressed single sideband (SSB) modulation. Our experiments demonstrate sideband suppression of /spl sim/28 dB at only a 2.9-GHz offset for single subcarrier amplitude modulated at 622 Mb/s. Furthermore, the hyperfine blocking filter can be tuned for simultaneous optical SSB and strong carrier suppression to /spl sim/30 dB lower in optical power than the unsuppressed sideband.

A microwave frequency shift keying optoelectronic oscillator (FSK-OEO) based on an optical single-sideband (OSSB) modulator is proposed and experimentally demonstrated. In the proposed FSK-OEO, a dual-drive Mach-Zehnder modulator (DDMZM) is employed to implement the optical single sideband modulation through the 90° phase shift method. By appropriately setting the amplitude of the coding signal applied to the DC port of the DMZM, a FSK microwave signal is generated. In the experiment, 9.995/10.004 GHz and 10.371/11.014 GHz microwave FSK signals were successfully generated by using the proposed OEO scheme. This scheme can generate high-frequency and low-phase-noise FSK signals without relying on high-frequency signal sources. Additionally, the pulse compression performance of the generated signals was also demonstrated.

In the paper, we proposed a simple method to generate two millimeter-wave (MMW) signals for radio-over-fiber (RoF) systems. Firstly, we utilized two cascaded dual-drive Mach-Zehnder modulators (DD-MZMs), both biased at the maximum transmission bias point (MATBP), to implement frequency octupling. And then, a wavelength division multiplexing demultiplexer (WDM Demux) is followed to filter out the −4 order optical carriers of the second DD-MZM's output to enable an optical single side-band (OSSB) modulation by only modulating the baseband data onto the −4 order optical carrier. On the other hand, the +2 order optical carrier of the first DD-MZM's output is filtered out based on an optical splitter (OS) and an optical rectangle band-pass filter (ORBPF). After that, the +2 and the −4 order optical carriers are combined to be transmitted in an identical fiber path. Finally, a 45 GHz and a 60 GHz MMWs were generated simultaneously with a 7.5 GHz local oscillator (LO), by self-heterodyning these optical carriers in a photonic detector (PD). After 50 km single-mode fiber (SMF) transmission distances, the 45 GHz and the 60 GHz MMWs were maintaining good performance with clearly open eye diagrams and power penalties of 0.6 dB and 1.1 dB, respectively, at a bit-error-rate (BER) of 1×10−9.

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.

We theoretically and experimentally investigate the measurement of the transfer function of optical devices using single-sideband modulation. The accuracy of this technique is found to strongly depend on a high suppression of the unwanted sideband.

To distribute microwaves over fibers, optical single-sideband (SSB) modulation signals are preferred to optical double-sideband (DSB) modulation signals. This study investigates an optically injected semiconductor laser at period-one nonlinear dynamics for optical DSB-to-SSB conversion. For the operating microwave frequencies up to 40 GHz investigated in this study, the proposed system regenerates or even enhances the microwave features of an optical DSB input while converting its optical feature into SSB with an intensity difference of at least 20 dB. The bit-error ratio at 622 Mb/s is down to 10(-9) with a sensitivity improvement of up to 3 dB. The proposed system can be self-adapted to certain changes in the operating microwave frequency and can operate stably under certain fluctuations in the input optical power and frequency.

In this work, we experimentally demonstrate a 100Gb/s/λ downstream transmission link for coherent passive optical networks (PONs) up to 50 km, achieving an optical power budget of 29 dB through polarization multiplexing (PolMux) of two 50 Gb/s channels using multiband carrierless amplitude phase modulation (multiCAP) and optical single side band (OSSB) modulation. Additionally, we introduce a separate PolMux 50 Gb/s link that presents an optical power budget of 38.7 dB. Both links have been achieved using a simplified polarization-demultiplexing heterodyne coherent receiver. The robustness of the system is experimentally evaluated by analyzing its response to various input states of polarization. The transmission has been accomplished using 10 GHz electrical bandwidth devices at both the transmission and receiving ends, thereby paving the way for low-cost 100G links suitable for applications such as PONs.

A new analytical model is presented to study nonlinear distortion due to cross-phase modulation in dispersive and nonlinear wavelength-division-multiplexing microwave fiber-optic links. The model is not based on the pump-probe approach. Hence, it can be used to analyze a larger variety of links, including, in particular, electrooptical upconversion links. Our simulations and experiments show that the model predicts the nonlinear distortion due to cross-phase modulation quite accurately, even when the modulating microwave frequency is in tens of gigahertz and the fiber length is in tens of kilometers. Detailed analyses of the distortion due to cross-phase modulation for links with optical single-sideband modulation are presented. Measured results for optical single-sideband are shown to match our theoretical predictions very well. Our results show that the nonlinear distortion due to cross-phase modulation can be a limiting factor for optical launch power in wavelength-division-multiplexing microwave fiber-optic links; moreover, the maximum possible nonlinear distortion level for a higher frequency may be lower than that for a lower frequency. Also presented are some simple approximations for a quick estimate of the level of the nonlinear distortion

We propose a technique for the generation of broadband optical single sideband modulated signals. The technique is based on optically processing an optical double sideband signal using stimulated Brillouin scattering effect. An unwanted sideband suppression over 40 dB in a broadband range from 50 MHz to 20 GHz is experimentally demonstrated. In addition, we apply the generated optical single sideband signal for the spectral characterization of polarization dependent parameters of optical components. The experimental characterization of the polarization dependent loss and the differential group delay of a phase-shifted fiber Bragg grating is performed in order to demonstrate the feasibility of the technique.

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 novel optical single sideband (OSSB) modulation scheme is proposed based on a phase-modulator (PM) and a tunable optical band pass filter (TOBPF) composed by a vertical-cavity surface-emitting laser (VCSEL) and an optical circulator (OC).