Double Sideband Suppressed Carrier Modulation Research Articles

Wavelength Reuse in an RoF Link Based on CS-DSB, Coherent Detection and DSP

Wavelength reuse in a bidirectional radio over fiber link based on carrier-suppressed double-sideband (CS-DSB) modulation, coherent detection, and digital signal processing (DSP) is proposed and experimentally demonstrated. At the center office, an optical single-sideband with carrier (OSSB+C) signal is generated and distributed to the base station. The wavelength reuse at the base station is implemented by directly modulating the downstream OSSB+C signal with an upstream signal based on CS-DSB modulation. The modulated upstream signal is sent to the center office where a coherent receiver and a DSP unit are used to recover the upstream signal by eliminating the crosstalk from the downstream signal, and at the same time, to cancel the phase noise from the laser source. An experiment is performed. The transmission of a 16-QAM downstream microwave vector signal and a 16-QAM upstream microwave vector signal over a 17-km single-mode fiber (SMF) is experimentally demonstrated. The power penalty caused by the wavelength reuse is less than 0.8 dB.

Microwave Photonic Frequency Up-Convertor With Frequency Doubling and Compensation of Chromatic-Dispersion-Induced Power Fading

A novel photonic frequency-doubling up-convertor with compensation of chromatic-dispersion-induced power fading is proposed and experimentally demonstrated based on the cascaded structure of a Mach–Zehnder modulator (MZM) and a dual-parallel Mach–Zehnder modulator (DPMZM). The MZM is driven by a local oscillator signal biased at the null point for carrier-suppressed double-sideband modulation. The DPMZM is single-port driven by the intermediate-frequency signal and the other port is matched with a 50-Ω resistance. By adjusting the dc biases of the DPMZM, the power fading induced by chromatic dispersion can be compensated at any frequency. Experimentally, comparing with the conventional up-conversion radio-over-fiber link with cascaded MZMs, the power fading in 60 and 80 km fiber links can be successfully compensated and a 26.7 dB improvement in spurious-free dynamic range at 21.7 GHz for a link of 60 km can be achieved by using the proposed scheme.

On the effect of the extinction ratio and the modulation index on optical up conversion using DSBSC modulation and transmitting over different fiber links

Several methods of millimeter wave up conversion based on Double Sideband Suppressed Carrier (DSBSC), Double Sideband with Carrier (DSB-C) and Single Sideband (SSB) using Mach Zehnder Modulator (MZM) have been reported. The DSBSC provides high receiver sensitivity, high spectral efficiency against DSB-C and SSB Modulation techniques. However, the signal in DSBSC suffers due to non linear electro-optical conversion response and imperfect power splitting ratio of the MZM. The imperfect splitting ratio of the MZM is caused by asymmetric power-splitting Y-branches due to the fabrication tolerances leading to a finite Extinction Ratio (ER). If this signal is transmitted over a fiber, it will suffer more degradation due to the chromatic dispersion, thus reducing the transmission distance. In this paper, the impact of the ER and the Modulation Index (MI) on the carrier and the higher order sidebands suppression in DSBFC is analyzed theoretically and by simulation. Our results show that, with the on optimum selection of the ER and the MI of the MZM, Optical Carrier Suppression Ratio (OCSR) and higher order sideband suppression ratio (SSR) increases. The analysis is further extended to determine the effect of chromatic dispersion over different lengths of the fiber. The results obtained by numerical analysis and by simulation show excellent agreement.

Double sideband suppressed carrier modulation for stable fiber delivery of radio frequency standards

We theoretically and experimentally investigate the properties of a double sideband suppressed carrier modulation transmission scheme for long distance microwave frequency standard dissemination. The proposed method effectively doubles the transmitted frequency obtaining enhanced phase noise and stability performance. Suppressing the optical carrier also eliminates the dispersion induced signal fading. Important transmission parameters like optical modulation depth and linearity are also improved. Allan deviation and phase noise measurements prove the superior performance of the proposed modulation format.

Frequency-doubling optoelectronic oscillator based on destructive interference

A frequency-doubling optoelectronic oscillator (OEO) using two cascaded modulators based on destructive interference is proposed and experimentally demonstrated. In the proposed system, we utilize a cascaded modulator including a phase modulator and an intensity modulator, which implements a carrier-suppressed double-sideband modulation based on destructive interference to generate a frequency-doubled microwave signal. Meanwhile, the phase modulator is connected by a chirp fiber Bragg grating in the loop, which forms a microwave photonic filter to select the fundamental frequency signal in the OEO loop. As a result, a frequency-doubled microwave signal at 17.9 and 20.5 GHz is generated, respectively. The phase noises and the long-term stability of the generated microwave signals are also investigated.

Comb-Based RF Photonic Filters Based on Interferometric Configuration and Balanced Detection

We demonstrate a novel technique to improve radio frequency (RF) performance such as RF gain and noise figure (NF) for comb-based RF photonic filters. While conventional RF photonic links use a dual-output modulator and balanced detection, this RF photonic filter utilizes an interferometric configuration with double sideband suppressed carrier modulation and balanced detection. This technique can simultaneously provide filter tunability, 6-dB RF gain increase, and noise cancellation. The RF gain and NF of the RF photonic filter are improved to approximately 0 and 24 dB, respectively. With the improved RF performance, we perform the tuning of the filter center frequencies from 2 to 8 GHz with no baseband filter response (<;-38 dB), no RF power fading, while maintaining good filter shape (sidelobe suppression and stopband attenuation >32 dB).

All-Optical Frequency Shifter Based on Stimulated Brillouin Scattering in an Optical Fiber

A new optical frequency shifter that can shift the light frequency in the microwave or millimeter-wave frequency range is presented. It is based on the use of stimulated Brillouin scattering gain and loss spectrums in an optical fiber to suppress one sideband of a double-sideband suppressed carrier modulation signal while amplifying the other sideband. The new optical frequency shifter only involves optical components and is capable of operating over a wide frequency range with low spurious generation and with tunable capabilities. It can be also used as a single-sideband suppressed carrier modulator. Experimental results demonstrate a 20 GHz frequency shift with a 25 dB signal-to-noise ratio and a widely tunable frequency shifting operation.

Demonstration of optical frequency quadrupling combined with direct/external signal double-sideband suppressed-carrier modulation

This study experimentally demonstrates the performance of optical frequency quadrupling generation and base-band signal up-conversion techniques based on the cascaded single-electrode Mach–Zehnder modulator (SEMZM) using different signal modulation schemes. The optical signals in microwave band with double-sideband suppressed-carrier (DSB-SC) modulated format exhibit that the receiver sensitivity and the spectral efficiency are maximized and the power penalty over long-distance delivery is minimized. A simple configuration and low-frequency bandwidth requirement for both electrical and optical components in the proposed schemes also are demonstrated.

Photonics-based microwave frequency measurement using a double-sideband suppressed-carrier modulation and an InP integrated ring-assisted Mach–Zehnder interferometer filter

A photonic system capable of estimating the unknown frequency of a CW microwave tone is presented. The core of the system is a complementary optical filter monolithically integrated in InP, consisting of a ring-assisted Mach-Zehnder interferometer with a second-order elliptic response. By simultaneously measuring the different optical powers produced by a double-sideband suppressed-carrier modulation at the outputs of the photonic integrated circuit, an amplitude comparison function that depends on the input tone frequency is obtained. Using this technique, a frequency measurement range of 10 GHz (5-15 GHz) with a root mean square value of frequency error lower than 200 MHz is experimentally demonstrated. Moreover, simulations showing the impact of a residual optical carrier on system performance are also provided.

An intensity modulation and coherent balanced detection intersatellite microwave photonic link using polarization direction control

A simple approach for high loss intersatellite microwave photonic link with intensity modulation and coherent balanced detection is proposed. In the transmitter, the double sideband-suppressed carrier (DSB-SC) modulated optical signal and optical carrier (OC) are combined by employing a polarization combiner to chose and control the signals polarization directions, while in the receiver, they are selected respectively by using a polarization splitter for they have orthogonal polarization directions. The separated DSB-SC signal and OC put into balanced detectors and the coherent detection is realized without a local oscillator (LO). At the output, the fundamental signal is augmented and the third-order distortion is suppressed for the DSB-SC modulation, the second-order distortion is removed for the balanced detection and the noise is reduced for the polarization direction control. The signal to noise and distortion ratio (SNDR) can be optimized by adjusting the power of OC and modulation index. The simulation results show that, a SNDR higher than 30 dB can be obtained for the proposed method, which is in agreement with the theoretical analysis.

Frequency-Doubling Optoelectronic Oscillator Using DSB-SC Modulation and Carrier Recovery Based on Stimulated Brillouin Scattering

A tunable frequency-doubling optoelectronic oscillator (OEO) is proposed and experimentally demonstrated, of which the novelty lies in the conjunction of the double-sideband suppressed carrier (DSB-SC) modulation and the carrier recovery based on stimulated Brillouin scattering (SBS) effect. Frequency-doubled signals are generated via the DSB-SC modulation, which is realized by using a polarization modulator (PolM) in combination with an optical polarizer. Then, the gain provided by the SBS effect is used to recover the suppressed optical carrier, such that a fundamental-frequency oscillating required in the OEO loop is maintained. In the experiment, frequency-doubled microwave signals at 6.1 and 20 GHz are generated and analyzed. Meanwhile, the stability of the generated signals is also investigated.

Ultrafast and broadband frequency chirp signal generation using a high-extinction-ratio optical modulator

We successfully demonstrate ultrafast frequency sweep signal generation using the double-sideband suppressed carrier modulation technique with a high-extinction-ratio optical modulator that helps realize clear signals with no filters. The resultant sweep rate was achieved at 3.67 × 10(16) Hz/s with an extinction ratio above 25 dB, which corresponds to a bandwidth of 11 GHz with a pulse duration of 300 ns.

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.

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.

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.

Effects of Direct Current Bias-Drifting on Radio on Fiber Link

The effects of direct current (dc) bias-drifting on radio on fiber (RoF) links are quantitative investigated and simulated. Single sideband (SSB) modulation and carrier suppressed double sideband (CS-DSB) modulation RoF links are considered, power variation of targeted signal and harmonic suppression on account for bias-drifting are calculated and evaluated. Our results suggest that power variation can be maintained within 1.1 dB with dc bias drift e less than 5% in the SSB modulation RoF link and the degradation of harmonic suppression is evident with e exceed 2% in the CS-DSB modulation RoF link.

Phase Stability Measurement of an Optical Two-Tone Signal Applied to a Signal Reference Source for Millimeter and Sub-Millimeter Wave Interferometer

Abstract Local signal generation with high phase stability is one of the key elements of an interferometer system. In the ALMA (Atacama Large Millimeter/submillimeter Array) project, we have plans to generate and transmit a micro/millimeter-wave LO (Local Oscillator) reference signal as an optical two-tone signal. To realize this, we introduce a method to generate an optical two-tone signal by double sideband suppressed carrier modulation with a lithium niobate ($\mathrm{LiNbO}_3$) Mach–Zehnder optical modulator. The phase instability of the LO signal causes a loss of coherence in the interferometer. We measured the phase instability and estimated the coherence loss while assuming the highest frequency of ALMA LO. The observed Allan standard deviation for 22 GHz was $1.9 \times 10^{-14}$ at 1 s. Additional noise was found at a longer time scale than 4 s; however, the reason is not well understood at this stage. If this additional noise was classified as white frequency noise, the estimated coherence loss was 5.2% when 938 GHz frequency and a 100-s integration time were assumed. On the other hand, if this additional noise was caused by some other effect, for example phase fluctuation of the amplifier, the coherence loss was estimated to be 0.33% at 938 GHz frequency (100 s).

All-optical modulation format conversion from frequency-shift-keying to phase-shift-keying

We have realized a novel optical modulation format conversion using double-sideband suppressed-carrier modulation. An optical wideband frequency-shift-keying (FSK) signal, generated by an external FSK modulator, can be directly converted into an optical phase-shift-keying (PSK) signal, where the FSK signal having two spectral components was fed to an optical intensity modulator followed by an optical bandpass filter. Optical frequency of the FSK signal was mapped into optical phase of the bandpass filter output whose phase deviation depends on a chirp of the FSK signal.We demonstrated modulation format conversion from FSK to PSK at 10 Gbps, by using a high-speed optical FSK modulator and a dual electrode Mach-Zehnder intensity modulator.

Generation of millimetre-wave signals by stimulated Brillouin scattering for radio over fibre systems

A new simple method for an all-optical generation of a radio frequency carrier is presented, which is based on stimulated Brillouin scattering (SBS) in an optical fibre and the creation of harmonics by double sideband suppressed carrier modulation. For the setup inexpensive standard components of optical telecommunications can be used.

All-optical double-sideband suppressed-carrier modulation of semiconductor lasers

We demonstrate theoretically and verify experimentally that injection locking may be used to achieve double-sideband suppressed-carrier modulation of semiconductor lasers. Our theoretical investigation explains the suppression of the optical carrier and illustrates the dominant role of the phase in prescribing the response of the injected laser.