Polarization Division Multiplexing Mach-Zehnder Modulator Research Articles

All-optical, filter-free, image-reject, and fundamental/sub-harmonic downconverted RoF link

An all-optical, image-reject, and fundamental/sub-harmonic downconverted radio-over-fiber (RoF) link using a polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) and fiber-dispersion effect is proposed. At the remote antenna unit, the receiving radio frequency (RF) signal and the local oscillator (LO) signal are used to drive two sub-MZMs of the PDM-MZM. After a length of optical fiber transmission, at the central office, by using the fiber-dispersion effect and controlling the polarization controller to introduce an appropriate phase shift between the RF and LO sidebands, image rejection is achieved and power fading is avoided simultaneously. Because the scheme is a simple and all-optical system without electrical frequency-dependent devices or filters, it has a good image-reject capability over a large working frequency range. Besides, the downconverter in sub-harmonic mode can decrease frequency requirement of the LO signal. Experimental results indicate that in the fundamental and sub-harmonic downconverters, for a single-tone signal, IRRs are over 47 dB. Image rejection for the 100-Mbaud 16-QAM signal and demodulated desired IF signal with a good EVM of less than 7% are realized. The proposed structure can be applied in RoF systems and microwave and millimeter-wave receivers.

Photonic-assisted multi-format dual-band microwave signal generator without background noise.

We report a photonic approach to generate background-free multi-format dual-band microwave signals based on a single modulator, which is suitable for high-precision and fast detection of radars in complex electromagnetic environments. By applying different radio-frequency signals and electrical coding signals to the polarization-division multiplexing Mach-Zehnder modulator (PDM-MZM), the generation of dual-band dual-chirp signals or dual-band phase-coded pulse signals centered at 10 and 15.5 GHz is experimentally demonstrated. Furthermore, by choosing an appropriate fiber length, we verified that the generated dual-band dual-chirp signals are not affected by chromatic-dispersion induced-power fading (CDIP); meanwhile, by autocorrelation calculations, we got high pulse compression ratios (PCRs) of 13 of the generated dual-band phase-encoded signals, showing that the generated phase-encoded signals can be emitted directly without extra pulse truncation operation. The proposed system features a compact structure, reconfigurability and polarization independence, which is promising for multi-functional dual-band radar systems.

RF Self-Interference Cancellation and Frequency Downconversion With Immunity to Power Fading Based on Optoelectronic Oscillation

We report a photonic approach to achieve simultaneous radio frequency (RF) self-interference cancellation (SIC) and frequency downconversion with immunity to power fading based on an optoelectronic oscillator (OEO) for an in-band full-duplex (IBFD) radio-over-fiber (ROF) system. A dual-drive Mach–Zehnder modulator (DDMZM) in a polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) is used to cancel the RF self-interference (SI) signal and generate optical carrier-suppressed double sidebands (CS-DSBs) of the signal of interest (SOI). Meanwhile, another DDMZM in the PDM-MZM is used to construct an OEO loop to generate optical CS-DSBs of the local oscillation (LO) signal. After detection at a photodetector (PD), a frequency downconverted signal is recovered with the RF self-interference cancellation (SIC). The proposed scheme can directly cancel the RF SI signal in the optical domain, meaning that it can overcome the limitation of SIC in the electrical domain. With the phase compensation introduced by a polarization controller, the desired signal is unaffected by the power fading over fiber transmission, which is significant for IBFD ROF systems. In addition, instead of an external microwave source, an OEO loop is used to generate an LO signal with a high spectral purity, which is very promising for integrated microwave photonics systems.

84 GHz millimeter-wave PAM4 signal generation based on one PDM-MZM modulator and one polarizer without DAC and filters

In this paper, a novel scheme to employ one external polarization division multiplexing Mach–Zehnder Modulator (PDM-MZM) and one polarizer to generate millimeter-wave four-level pulse amplitude modulation (PAM4) signal is proposed without the usage of expensive and power hungry digital-to-analog converter (DAC). Firstly, we theoretically derive the generation conditions for the mm-wave PAM4 signal scheme. Based on this cost-effective scheme, 6 Gbaud PAM4 signal carried by 84 GHz millimeter-wave transmission over 15 km single-mode fiber (SMF-28) with only 0.5 dB power penalty without any CD compensation is experimentally demonstrated. Furthermore, VPI simulation software is employed to numerically simulate the mm-wave PAM4 signal generation and explore the influences of polarization rotation of the polarizer and direct current (DC)-Bias on the performance of generated W-band signals. In a word, it would be a promising scheme for future 5G short-reach intensity modulation and direct detection (IM/DD) system.

QAM Vector mm-Wave Signal Generation Based on Optical Orthogonal Polarization SSB Scheme By a Single Modulator

Millimeter-wave (mm-wave) has become an attractive technique in the fifth generation (5G) because it meets the demand of explosive increase in data traffic. In this study, we propose and demonstrate the generation of quadrature amplitude modulated (QAM) vector mm-wave signal employing optical orthogonal polarization single sideband (SSB) modulation, which employs a single polarization-division multiplexing MachZehnder modulator (PDM-MZM). Based on our scheme, there is no inter-band crosstalk and inter-polarization signal-signal beat interference (SSBI). In our scheme, the two sub-modulators in PDM-MZM both work within their linear modulation range. After PDM-MZM, the two optical SSB signals are orthogonally polarized. By using an interleaver (IL), the low sideband (LSB) and upper sideband (USB) optical signals in the two polarization directions are extracted respectively. In addition, IL also suppresses the unwanted components of the opposite orthogonally polarized signal. We demonstrate the generation of two independent 28 GHz 12 Gbaud quadrature-phase-shift-keying (QPSK) and 6 Gbaud 16-ary quadrature amplitude modulation (16-QAM) signals. 65 km single-mode fiber (SMF) transmission is achieved with the bit-error-rate (BER) below 20% forward-error-correction (FEC) soft-decision threshold of 2.4 102 without dispersion compensation. We also demonstrate the generation of two independent 28GHz 1 Gbaud 64-QAM signals and transmission SMF over 10-km with the BER below 20% FEC soft-decision threshold of 2.4 102. Since the LSB and USB signals are on opposite polarization sides, the inter-band crosstalk and the inter-polarization SSBI can be significantly reduced. Because SSB modulation scheme is deployed, our proposed QAM vector signal generation system is robust to fiber dispersion.

Generation and anti-dispersion transmission of quadrupling-bandwidth dual-chirp microwave waveform based on a polarization-division multiplexing Mach–Zehnder modulator

We propose and demonstrate a photonic approach to generate and transmit a quadrupling-bandwidth dual-chirp microwave waveform with anti-dispersion transmission. Commonly, dual-chirp microwave waveforms are generated by double-sideband modulation, which brings severe chromatic-dispersion-induced power fading (CDIP) over fiber transmission. In this scheme, we perform optical carrier suppression via a polarization controller based on an integrated polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) to eliminate the CDIP. Moreover, by properly adjusting two bias voltages of PDM-MZM, we find that the bandwidth of the generated dual-chirp microwave signal is quadrupled. It is worth mentioning that we just need to operate in the central office to realize the above-mentioned functions and no optical filters are needed, which significantly improves the limitation of the devices. The method is analyzed theoretically and proved experimentally, which is of great significance for improving range-Doppler resolution and the detection capability of radars for one-to-multi base stations over fiber transmission.

Polarization Division Multiplexing-Based Hybrid Microwave Photonic Links for Simultaneous mmW and Sub-6 GHz Wireless Transmissions

A new hybrid microwave photonic link based on a polarization division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed. The link enables co-transmission of millimeter-wave (mmW) and sub-6 GHz wireless signals over a seamless single-mode fiber (SMF) and free-space optics (FSO) channels. Optimization of the chromatic dispersion (CD)-induced power fading regardless of the power fading due to the non-deterministic atmospheric turbulence (AT) is simultaneously demonstrated. Extensive simulation analysis is first presented to examine (i) the impact of CD on mmW (25 GHz) and sub-6 GHz (2.6 GHz) signals, envisioned for the 5th generation networks, and (ii) optimization of CD-induced power fading by changing the phase relations between the optical carrier and optical sidebands in each polarization channel using single tunable polarization controller. A proof-of-concept experiment is finally performed to simultaneously deliver 25 GHz and 2.6 GHz signals with 4/16/64-quadrature amplitude modulation over (i) 20 km SMF and 2 m radio wireless link and (ii) 20 km SMF, 4.2 m FSO (with AT) and 2 m radio wireless links. The optimization of the CD-induced power fading is experimentally verified and link performance shows high tolerance to CD with no power penalties and the measured error vector magnitudes well below the required limits. The predicted bit error rates are also below the forward error correction threshold of $2 \times {10^{ - 4}}$.

Suppression of third-order intermodulation distortion in analog photonic link based on an integrated polarization division multiplexing Mach–Zehnder modulator

A simple and linear analog photonic link (APL) based on a single integrated polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is proposed with suppressed third-order intermodulation distortion (IMD3). By properly selecting the modulation indexes of radio frequency (RF) signals and bias angles in the two sub-modulators, the electric/optical power ratio is changed and thus two nonlinear distortion signals with opposite phases are constructed to cancel out IMD3 of the link. Therefore, the IMD3 can be suppressed and the spurious-free dynamic range (SFDR) of the system can be improved. Only one electrode in each sub-modulator is used in the experiment. Experimental results show that compared with the conventional link based on a single MZM, 33.7-dB reduction of IMD3 is achieved and an enhancement of 17.6 dB in SFDR can be obtained. Besides, the proposed APL is test by a 16 quadrature amplitude modulation (QAM) RF signal and the error vector magnitude (EVM) and adjacent channel power ratio (ACPR) of the link are measured.

Photonic generation of frequency-doubled microwave waveform based on a PDM-MZM modulator

A novel and simple photonic approach for frequency-doubled microwave waveforms generation based on a polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is proposed and experimentally demonstrated. The PDM-MZM is driven by a local oscillation (LO) signal through a 90 degree hybrid coupler. One sub-modulator of the PDM-MZM is biased at the peak transmission point and the other sub-modulator is biased at the null transmission point. The optical signals from the two arms are polarization multiplexed at the output of the PDM-MZM and then injected into a photodetector (PD) for photoelectrical conversion. By properly controlling the amplitudes of the LO signal, the triangular and square waveforms with a repetition rate twice the frequency of the LO signal can be generated. This scheme has features of compact, low-cost structure and simple operation. Simultaneously, the frequency of the generated waveform can be tuned over a wide bandwidth since there is no optical or electrical filter involved.

6–40 GHz photonic microwave Doppler frequency shift measurement based on polarization multiplexing modulation and I/Q balanced detection

A novel optical approach to implement broadband Doppler frequency shift (DFS) measurement is proposed and demonstrated. Through I/Q balanced detection using a polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) and two balanced photodetectors, the concerned microwave DFS is estimated with clear direction discrimination and a significant improved resolution. In the experiments, the DFSs from -100 to 100 kHz in 20-kHz step are successfully measured and estimated for microwave signals with the operating frequency from 6 to 40 GHz. The error of measuring is calculated to be less than 8 Hz. The approach is uncomplicated and manageable to implement, which provides an alternative solution for future wideband electronic systems such as Doppler radar, satellite communications or electronic countermeasures.

Reconfigurable photonic generation of background-free microwave waveforms with multi-format

Photonic generation of background-free microwave waveforms with multi-format and parameter tunability is proposed and demonstrated. In the approach, the polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is employed to modulate the linearly polarized lightwave. After properly adjusting the modulation indices of the PDM-MZM, background-free square and triangular waveforms will be obtained after heterodyne detection; by driving the polarization modulator with binary sequence, the structure can also generate background-free digital modulation signals, including amplitude shift keying (ASK), phase shift keying (PSK) and frequency shift keying (FSK) signals via the same structure. The approach is investigated by simulations. Square and triangular waveforms with repetition rate of 20 GHz are obtained, and digital modulation signals with modulation rate of 2 Gbit/s are generated. The proposed generator shows flexible tunability of carrier frequency, bit rate and modulation format. The stability of the structure is verified by phase drift, polarization error and RF driven voltage offset.

Photonic generation of background-free binary and quaternary phase-coded microwave pulses based on vector sum.

A photonic microwave phase-coded pulse generator is proposed and experimentally demonstrated based on the principle of vector sum. The key component of the proposed pulse generator is an integrated polarization-division multiplexing Mach-Zehnder modulator (PDM-MZM) and a 90° hybrid coupler. By properly setting the data sequences applied to the specially biased PDM-MZM, binary and quaternary phase-coded microwave pulses (PCMPs) that are free from the background signals can be generated. Since no filters and polarization adjustment are involved, the proposed pulse generator is characterized by a simple structure, low-loss, flexible frequency tunability and high long-term stability. The experimental results show that background-free 4 Gb/s Barker and Frank PCMPs at 18 GHz and 2 Gb/s Barker and Frank PCMPs at 24 GHz are successfully generated. The calculated pulse compression ratio and peak-to-side lobe ratio are in good agreement with the theoretical values.

Carrier-frequency-doubled photonic microwave vector signal generation based on PDM-MZM

A simple method based on an integrated polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) to produce a carrier-frequency-doubled vector signal is presented and experimentally demonstrated. In this structure, the upper sub-MZM is driven by I/Q signals and biased at the quadrature point to modulate a baseband vector signal on the optical carrier. The lower sub-MZM is driven by a LO signal and is biased at the maximum transmission point (MATP) to generate the optical carrier and second-order sidebands. By filtering the negative second-order sideband via an optical bandpass filter (OBPF) and suppressing the optical carrier via polarization controller (PC), a carrier-frequency-doubled vector signal is generated at the photodetector. Due to the adoption of LO frequency-doubled technique, the system’s requirement of a high-frequency LO is relaxed. In a proof-of-concept experiment, 300 MSym/s QPSK signal with a carrier frequency of 16 GHz is obtained by 8 GHz LO signal. Besides, 25-km fiber transmission of the generated QPSK signal is demonstrated. When the optical power obtained after fiber transmission is higher than -4 dBm, the BER after demodulation is less than 8×10−10. Moreover, generation of vector signal with other formats is verified.

Simple and Flexible Photonic Microwave Waveform Generation With Low RMSE of Square Waveform

A simple and flexible photonics-assisted approach based on an integrated polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) and a balanced photodetector (BPD) to generating microwave waveform is proposed. The sub-MZMs of PDM-MZM are biased at peak and null points. Square and trapezoid waveforms are generated by controlling the PC and driven sinusoidal signal power. Triangle and sawtooth waveforms are also obtained with the help of a 90° microwave phase shifter (MPS). The proposed approach features simple structure, flexible frequency tunability, and easy implementation. Moreover, the problem of high root-mean-square error (RMSE) of square waveform is solved by this approach for the first time. An experiment is conducted to verify the approach. Different waveforms with the repetition rates of 3 and 5 GHz are generated. The RMSE of square waveform is reduced from 0.3328 to 0.2048 which is the lowest RMSE to the best of our knowledge.

Filter-free image-reject microwave photonic downconverter based on cascaded modulators.

As essential equipment of the receiver, a novel filter-free image-reject mixer based on a Mach-Zehnder modulator (MZM) and a polarization-division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed and experimentally demonstrated in this paper. The received radio frequency signal is applied to the MZM, and quadrature local oscillator signals are sent to the PDM-MZM, which includes two submodulators in parallel. After a polarization controller and a polarization beam splitter, quadrature intermediate frequency (IF) signals are obtained by two photodetectors. Image rejection is implemented by combining quadrature IF signals via an electrical 90° hybrid coupler. The scheme uses no filter, so the working frequency can be widely tuned and effective spectrum utilization is achieved. Experimental results verify that image rejection ratios can reach 50dB. Moreover, the variation of the conversion gain is lower than 2dB.

A simple and tunable photonic generation of frequency-doubled triangular waveform based on two cascaded modulators

A simple and tunable photonic approach for frequency-doubled triangular waveform generation is proposed and experimentally demonstrated. The approach is based on an intensity modulator (IM) and a cascaded polarization division multiplexing Mach–Zehnder modulator (PDM-MZM). The IM and the upper arm of the PDM-MZM are driven by the same LO signal, with the former biased at the null point and the latter at the maximum transmission point. By adjusting the modulation index of the upper arm and the direct current (DC) bias of the lower arm of the PDM-MZM, the frequency-doubled full-duty-cycle triangular waveform can be generated. The proposed approach does not use any electrical phase shifter or optical filter, it is easy to implement and exhibits the advantages of good frequency tunability. An experiment is conducted to verify the approach. Triangular waveforms with different repetition rates of 8 GHz and 10 GHz are generated.

A High Spectral Efficiency Microwave Photonic Link With Optimization of Chromatic-Dispersion-Induced Power Fading

A novel microwave photonic link to simultaneously realize high spectral efficiency and optimization of chromatic-dispersion-induced power fading based on dual-drive polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is proposed and demonstrated. Two microwave vector signals are IQ modulated on an optical carrier in one polarization state via the upper sub-MZM (IQ modulator) of the PDM-MZM. The optical carrier with orthogonal polarization state is unmodulated and transmitted together with the modulated optical signal. At the receiver, a polarization controller and polarizer are cascaded to change the phase of the optical carrier. By properly changing the phase of the optical carrier, the two microwave vector signals are respectively recovered and the chromatic-dispersion-induced power fading is optimized simultaneously. Since two microwave vector signals are transmitted over a single optical carrier, the spectral efficiency of the link is doubled. A proof-of-concept experiment is performed. The transmission of a 50-Msym/s 16-QAM signal and a 100-Msym/s QPSK signal both at 6 GHz over a 25-km SMF is realized, and its transmission performance in terms of error vector magnitude (EVM) and bit error rate (BER) is evaluated. The optimization of the chromatic-dispersion-induced power fading is also verified by the experiment.

Photonics-based multi-function analog signal processor based on a polarization division multiplexing Mach-Zehnder modulator.

A photonics-based multi-function analog signal processor based on an optical polarization division multiplexing dual-parallel Mach-Zehnder modulator is proposed and demonstrated, which can implement simultaneously photonic microwave phase shifting, upconversion/downconversion and filtering with excellent tunability. An experiment is carried out. Downconverted and upconverted phase shifters with phases continuously tuned from -180 to 180deg over 0-11 and 11-33GHz are implemented. Based on the frequency-mixed phase shifter, a four-tap microwave photonic filter that has the capability to select a frequency-mixed component is built. The proposed approach features multi-function, scalable independent channels, a wide bandwidth, and high tunability, which can find applications in beamforming networks, radio frequency frontends, and radio over fiber systems.

Large Bandwidth Photonic Microwave Image Rejection Mixer With High Conversion Efficiency

A photonic microwave image rejection mixer (IRM) with large operating frequency range and high conversion efficiency is presented in this paper. The scheme is achieved by using a photonic microwave phase shifter, which is based on a polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM). Thanks to the large operating frequency range of the photonic microwave phase shifter, the operating frequency of the proposed IRM can extend to 40 GHz. Besides, the system has high conversion efficiency, owing to the suppression of the optical carrier and application of balanced photodetector. To verify the scheme, an experiment is performed. Experimental results demonstrated large operating frequency range (5–40 GHz) and high image rejection ratio (40 dB) of the mixer. Compared with the conventional photonic microwave mixer, a 19-dB improvement of conversion efficiency is realized in the experiment.

Analog Photonic Link With Tunable Optical Carrier to Sideband Ratio and Balanced Detection

Optical carrier to sideband ratio (CSR) optimization and balanced detection are two effective techniques to improve the performance of an analogy photonic link (APL). Here, we proposed an APL where tunable optical CSR and balanced detection can both be implemented. A single integrated polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is used to generate a polarization multiplexed signal containing an optical carrier and two radio frequency modulated sidebands, and the optical CSR can be tuned from –15 to 15 dB by simply adjusting the direct current bias of the modulator. By optimizing the optical CSR in the proposed link, the link gain and noise figure (NF) are improved by 12 and 6.8 dB compared with conventional quadrature biased link. In addition, after balanced detection in the proposed link, the link gain, NF, third-order spurious free dynamic range (SFDR), and especially the second-order SFDR are further improved.