Search

Nonlinear distortion and chromatic dispersion are two long-standing limiting factors of radio-over-fiber (ROF) links. Here, we proposed an ROF link with both the two problems mitigated simultaneously. Furthermore, a tunable optical carrier-to-sideband ratio (CSR) can also be implemented in this simple system to improve the gain and the noise figure (NF) of the link. All these three factors are optimized in a simple ROF link which shows increased performance of the system. The scheme is based on a single dual-polarization Mach–Zehnder modulator (DPol-MZM). One bias voltage of the Dpol-MZM is employed to mitigate the nonlinear distortion. The polarization direction and the phase relationship of the modulated polarization multiplexed signal are used to adjust the CSR and suppress the dispersion, respectively, by adjusting a polarization controller (PC). In the experiment, 3–30-GHz RF signal is transmitted without power fading. A two-tone signal with the frequencies of 12.5 and 12.505 GHz is employed to verify the optimization of three main parameters of the ROF link [link gain, NF, and spurious-free dynamic range (SFDR)] where the link gain, NF, and SFDR are improved by 11.9, 5.8, and 14.5 dB, respectively, compared with conventional quadrature biased link based on one Mach–Zehnder modulator for 50-km single-mode fiber (SMF) transmission. Meanwhile, 100-Mbaud 16 quadrature amplitude modulation (QAM) signals centered at 12.5 and 14.7 GHz are used to verify the transmission performance. After dispersion compensation, nonlinear optimization, and CSR optimization, error vector magnitude (EVM) is improved from 17.03% to 2.97%. [ABSTRACT FROM AUTHOR]

A novel analog photonic down-conversion link based on a polarization modulator and a phase modulator with simultaneous linear optimization and chromatic dispersion-induced power fading compensation is proposed and experimentally demonstrated. By introducing an appropriate phase shift to the optical sidebands, chromatic dispersion-induced power fading is compensated, and third-order intermodulation distortion terms are eliminated in the same time. The scheme exhibits wide operating frequency range due to its no use of filters and frequency-dependent electrical or optical devices. The scheme is robust, as the operation of the polarization modulator and the phase modulator are independent of signal amplitude and bias voltage. Experimental results show that, for a 25-km transmission link, an improvement of more than 15.5 dB in spurious-free dynamic range is achieved and the dispersion-induced power fading is compensated at the same time. In addition, benefiting from the power compensation and significant suppression of IMD3, a 16QAM vector signal is demonstrated to have a good demodulation performance. [ABSTRACT FROM AUTHOR]

A photonic approach to generate dual-band polyphase-coded microwave signal with a tunable frequency multiplication factor is proposed. The scheme contains a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator, a polarization modulator (PolM), and a balanced detector. When the bias voltages of the DP-QPSK modulator is properly adjusted, a double-sideband signal will be generated with one sideband along the X polarization of the PolM, with the optical carrier and the other sideband along the Y polarization. Then, the PolM is employed to modulate the optical signal with a phase-coded microwave signal. After the photoelectric balanced detection, polyphase-coded microwave signals with frequency multiplication factors of one, two, and four can be generated. In addition, the proposed scheme can simultaneously produce two phase-coded microwave signals with different carrier frequencies. The proposed system finds a potential application in dual-band radar. In the experiment, a binary- and a quaternary-phase-coded signal with 5.5, 11, and 22 GHz carrier frequencies are generated. [ABSTRACT FROM AUTHOR]

A novel phase coded signal generator is proposed and experimentally verified. The scheme consists of a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator and a phase modulator in a Sagnac loop. By properly adjusting the bias voltages of the DP-QPSK modulator and the polarization direction of the signal, two-order optical sideband is polarization separated from the carrier and −2-order sideband. We can modulate the two-order optical sideband with phase coded data and two phase coded signals will be generated which are the beating products between the modulated two-order optical sideband and the unmodulated optical sidebands in balanced detector. The distinct advantage of our approach is that we integrate multiple functions into a compact system which can simultaneously generate dual-band and multi-phase coded signal with doubled and quadrupled frequency. In the experiment, 1-Gbit/s binary and quaternary phase coded signals with 11 and 22 GHz carrier frequencies are generated by using of a 5.5 GHz local oscillator signal. [ABSTRACT FROM AUTHOR]

We propose a multi-channel phase-modulated analog photonic link (APL) with linearization and mitigation of dispersion-induced power fading based on a polarization modulator (PolM). When the modulated signal from the PolM goes through a polarization controller and a polarization beam splitter (PBS), the odd- and even-sidebands of the phase-modulated signal can be separated into orthogonal polarization states and travel out from the two outputs of the PBS. By introducing a proper phase shift between two orthogonal polarization states, the third-order intermodulation distortion can be suppressed while the dispersion-induced power fading can be mitigated with different working frequency of the APL and different transmission length of the subchannel. Both theoretical analysis and experimental verification are given. Experimental results show the spurious free dynamic range of above 96 dB·Hz2/3 at the noise floor of –143 dBm/Hz, which is improved by 10.2 dB as compared with conventional phase-modulated APL. [ABSTRACT FROM AUTHOR]

Microwave I/Q up-converter is widely used in modern electronic systems to achieve single-sideband (SSB) up-conversion and vector modulation. However, due to the frequency-dependent mixer and quadrature coupler, conventional electronic I/Q up-converters suffer limited operating bandwidth. In this paper, a photonic microwave I/Q up-converter is proposed using a polarization-division multiplexing modulator. The I/Q up-conversion channels are built in all-optical methods without any frequency-dependent devices, so a wide operating bandwidth is obtained. Balanced detection is also realized to reduce the noise figure. In the experiment, SSB signals with wide operating bandwidth (14–40 GHz), high sideband and carrier suppression (>20 dB), and large spurious-free dynamic range (110.4 Hz2/3) are generated. 16 and 64 quadrature amplitude modulation vector signals with data rates of 400 and 600 Mb/s at 40-GHz carrier frequency are also demonstrated. Furthermore, subharmonic I/Q up-conversion with similar performance is also realized using the same structure, which can well reduce the frequency requirement of the local oscillator signal and the drive circuits. [ABSTRACT FROM AUTHOR]

A wideband photonic microwave single sideband (SSB) up-converter and an in-phase/quadrature (I/Q) modulator are proposed and experimentally demonstrated. The intermediate frequency (IF) and local oscillator (LO) signals are applied to the submodulators of a dual-parallel Mach–Zehnder modulator (DPMZM) for frequency up-conversion, and the phase of the generated radio frequency signal can be arbitrarily tuned through the working point of the DPMZM. Using a polarization division multiplexing DPMZM, a wideband photonic microwave I/Q frequency up-converter can be constructed for SSB up-conversion or I/Q modulation. In the experiment, SSB signals with well-suppressed carrier and undesired sideband are generated over a wide frequency coverage of the LO (16–40 GHz) and IF (2–8 GHz) signals. In the experimental demonstration of I/Q modulation, 16- and 64-quadrature amplitude modulation signals with a symbol rate of 100 MSym/s and a carrier frequency from 10 to 40 GHz are successfully generated with low error vector magnitudes. [ABSTRACT FROM PUBLISHER]

A wideband microwave Doppler frequency shift (DFS) measurement approach based on a single dual-parallel Mach–Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. The light wave is modulated by the transmitted and echo signals in the DPMZM to generate carrier suppressed double sidebands signals. Based on the phase difference and powers of the upper bands and lower bands of the modulated signal, the DFS value, as well as the sign, can be measured. An experiment is carried out. The DFS from –100 to +100 kHz at the carrier frequencies of 10, 20, 30, and 39 GHz is accurately measured with errors of less than 5 \times 10^ - 6 Hz. [ABSTRACT FROM PUBLISHER]

In this paper, a novel microwave photonic mixer based on a single integrated dual-drive dual-parallel Mach–Zehnder modulator (DD-DPMZM) is proposed. One submodulator is used to generate a single sideband (SSB) signal of the local oscillator, whereas the other submodulator is used to generate a double sideband signal of the radio-frequency signal. By adjusting the main dc bias of DD-DPMZM, we can suppress the optical carrier at the output of the DD-DPMZM. Mixed signals can be obtained after a photodiode. The structure features the advantages of high conversion efficiency and the elimination of dispersion-induced power fading. An experiment is carried out to verify the effectiveness of the scheme, and a significant improvement of 15.5 dB in conversion efficiency compared with the conventional photonic mixer is achieved. In addition, it avoids the influence of fiber dispersion. The proposed mixer is promising to find applications in future wideband wireless communication systems. [ABSTRACT FROM PUBLISHER]

A photonic approach to generate a phase-coded microwave waveform with frequency quadrupling is proposed and experimentally demonstrated in this paper. The system consists of a dual-parallel Mach–Zehnder modulator (DPMZM), a phase modulator (PM), a fiber Bragg grating (FBG), an optical coupler, and a photodetector. An optical carrier is modulated by a local oscillator (LO) in the DPMZM, and pure ±second-order sidebands are generated. Then, the two sidebands are separated by the FBG, and one of them is modulated by the coding signal through the PM. Both binary and quaternary phase-coded microwave signals with frequency quadrupling of the LO signal can be generated after detecting the recombined two sidebands. The proposed scheme is verified by experiments; phase-coded microwave waveforms at 24 and 12 GHz are generated by applying 6- and 3-GHz LO signals to the DPMZM, respectively. The pulse compression ratios of the generated waveforms are in good agreement with theoretical value. [ABSTRACT FROM PUBLISHER]

A simple scheme based on two cascaded intensity modulators to generate a flat optical frequency comb (OFC) is proposed and experimentally demonstrated. By setting the two controllable parameters of the intensity modulation (RF amplitude and DC bias), five comb lines with a comb flatness within 0.6 dB are generated. When cascaded with another intensity modulator, 25 comb lines with a spectral power variation of less than 0.9 dB are obtained. The scheme, with a high unwanted-mode suppression ratio 13.1 dB and very low RF signals 0.58Vπ, is relatively simple, cost-efficient and adjustable, with the frequency interval of the OFC varying with the microwave frequency applied to the modulators. [ABSTRACT FROM AUTHOR]

A frequency-multiplying optoelectronic oscillator (OEO) with a tunable multiplication factor to generate a frequency-quadrupled, sextupled, or octupled microwave signal without using an optical filter is proposed and experimentally demonstrated, for the first time to the best of our knowledge. In the proposed OEO, a polarization modulator (PolM), a polarization controller (PC), and an optical polarizer (Pol) function jointly as a Mach–Zehnder modulator (MZM). Microwave oscillation is achieved in the OEO by feedbacking the intensity-modulated signal to the PolM after photodetection, and the oscillation frequency is determined by the center frequency of an electrical bandpass filter (EBPF) in the loop. A frequency-multiplied microwave signal is generated by a joint use of the PolM and a second modulator to generate two sidebands at the \pm second, \pm third, or \pm fourth orders with the sidebands at other orders fully suppressed. By beating the two sidebands at a second photodetector (PD), a frequency-quadrupled, sextupled, or octupled microwave signal is generated. An experiment is performed. A fundamental microwave signal at 9.957 GHz is generated in the OEO loop, which is multiplied to generate a frequency-quadrupled, sextupled, or octupled microwave signal at 39.828, 59.742, or 79.656 GHz, respectively. The phase-noise performance of the frequency-multiplying microwave signal is also investigated. [ABSTRACT FROM PUBLISHER]

We propose and experimentally demonstrate a coherent millimeter wave radio-over-fiber (MMW-ROF) link employing mixed modulations with a simple digital signal processing (DSP) unit. At the transmitter, a light wave is intensity and phase-modulated by two microwave vector signals in a dual-parallel Mach–Zehnder modulator (DP-MZM). At the receiver, by using a 3-line optical frequency comb (OFC) signal as the optical local oscillator (OLO), the microwave vector signals can be photonically down-converted to intermediate frequency (IF) signals. Then, instead of a complex digital phase-locked loop (DPLL), simple algorithms are used to remove the laser phase fluctuation between two free-running lasers and do the demodulations. In the 25 km fiber transmission experiments, we successfully down-convert two 50 Msymbol/s 16-quadrature amplitude modulation (16-QAM) signals at 25 GHz and 24 GHz to intermediate frequencies of 2 GHz and 1 GHz. The transmission performance of the proposed link in terms of error vector magnitudes (EVMs) are also investigated. The results show that when the receiver optical power is -20 dBm, the measured EVMs are still less than 12.5% which satisfies the 3rd Generation Partnership Project (3GPP) standard. • A combed OLO is used for photonic down-conversion of MMW signals. • Multi-dimensional modulation facilitates full use of the light source. • Simple algorithms for laser phase noise elimination. [ABSTRACT FROM AUTHOR]