Dual-polarization Modulator Research Articles

Photonic generation of frequency-octupled microwave signal with reduced electrical local oscillator power and improved spectrum purity

Two cascaded dual-polarization modulators are proposed to generate frequency-octupled microwave signal without an optical filter. The dual-polarization modulator is a commercially available integrated device, which consists of a polarization beam splitter, a polarization beam combiner, and two Mach–Zehnder modulators (MZMs). By properly adjusting the phase difference between the two drive signals, the direct current bias points of the modulators, and the polarization state of the light wave after the modulator, a pure frequency-octupled signal with an optical sideband suppression ratio exceeding 23 dB and a radio frequency spurious suppression ratio (RFSSR) higher than 38 dB can be obtained. A comparison is made with a two series parallel MZM architecture. Simulation results show that the intrinsic conversion efficiency of the proposed method is improved by 2 dB and the RFSSR is also enhanced over a wide range of modulation index.

Performance analysis of coherent optical communication system for higher order dual polarization modulation formats

The ever increasing demand of data traffic due to emerging services and applications has evolved the need of high capacity, high speed and highly spectral efficient optical systems with advanced modulation formats. We compare the performance of single channel coherent optical system for 112Gb/s with Dual polarization modulation techniques i.e. DP- QPSK(Dual Polarization Quadrature phase shift keying), DP-16QAM(Dual Polarization −16 Quadrature amplitude Modulation) and DP-32QAM(Dual Polarization −32 Quadrature amplitude Modulation) with DSP (Digital Signal Processing)module for SSMF(standard single mode fiber) in terms of tolerance to fiber nonlinearities which is investigated through the effect of power and distance on %EVM and requirement of OSNR using numerical simulations. ned shows that the coherent optical systems with higher order modulation formats are less tolerant to fiber nonlinearities i.e the performance of DP-QPSK coherent systems with DSP module is better than the DP-16QAM and DP-32QAM coherent systems as they are more tolerant to fiber nonlinearities. The results obtained can be used for the design of compensation techniques for fiber nonlinearities in cohResults obtaierent optical systems using higher order modulation formats.

Filter-free photonic frequency sextupler operated over a wide range of modulation index

An integrated dual-polarization modulator is proposed to generate frequency-sextupled microwave signal without an optical filter. The dual-polarization modulator can achieve even-order optical sidebands suppression modulation along the orthogonal polarization directions with different modulation index. By properly adjusting the power relationship of the orthogonal polarization directions, two optical first-order sidebands will cancel each other out. Thus, a pure frequency-sextupled signal with an optical sideband suppression ratio (OSSR) exceeding 38dB and a radio frequency spurious suppression ratio (RFSSR) higher than 32dB is generated, which match well with the theoretical analysis. Since there is no requirement to carefully adjust the modulation index to achieve correct operation of the sextupler, it is much easy to implement. Furthermore, it is also proved to be valid that even if the extinction ratios of the MZMs, the polarization angle of the polarizer, and the direct current (DC) bias phase shift deviate from the ideal values to a certain degree, the performance of the generated frequency-sextupled microwave signal is still acceptable.

Time-Domain Waveform Synthesis Using a Dual-Polarization Modulator

This letter proposes a time-domain waveform synthesis based on a dual-polarization modulator that is driven by single-frequency radio frequency signals. This is achieved by applying a dual-polarization modulator to generate a polarization multiplexed optical signal. By controlling the parameters of the driving signals, multiple waveforms can be generated by synthesizing optical intensity profiles along two orthogonal polarization states. Compared with previously reported signal generators, the proposed time-domain waveform synthesizer is simple, compact, and easy to implement. The generation of triangular, flat-top, and sawtooth pulse trains with 5- and 10-GHz repetition rates are demonstrated in this letter. The results indicate that the proposed system is feasible and would find applications in optical signal processing and microwave photonic signal processing systems.

Photonic microwave frequency measurement with a tunable range based on a dual-polarization modulator.

This paper presents a novel photonic-assisted microwave frequency measurement scheme based on an integrated dual-polarization Mach-Zehnder modulator (DPol-MZM). The DPol-MZM is used to obtain a polarization multiplexing signal modulated by the microwave signal with the frequency to be identified. The obtained signal is split into two channels after propagating along a single mode fiber. The two divided parts are used to establish an amplitude comparison function (ACF) which provides frequency-power mapping. The proposed scheme is experimentally verified. The frequency responses of the two branches are nearly complementary; thus, a relatively steep ACF is obtained. A frequency measurement range from 2 to 28 GHz with an error of ±0.2 GHz is achieved. Moreover, the measurement range can be tuned by simply adjusting the polarization state of one channel. The proposed system is simple, and the measurement range can be easily adjusted.

Photonic generation of versatile frequency-doubled microwave waveforms via a dual-polarization modulator

We report a photonic approach to generate frequency-doubled microwave waveforms using an integrated electro-optic dual-polarization modulator driven by a sinusoidal radio frequency (RF) signal. With active bias control, two MZMs of the dual-polarization modulator operate at minimum transmission points, a triangular waveform can be generated by a parameter setting of modulation index. After introducing a broadband 90° microwave phase shifter, a square waveform can be obtained by readjusting the power relationship of harmonics. The proposal is first theoretically analyzed and then validated by simulation. Simulation results show that a 10GHz triangular and square waveform sequences are successfully generated from a 5GHz sinusoidal RF drive signal, and the performance of the microwave waveforms are not influenced by the finite extinction ratio of modulator.

A Bidirectional Fiber-Wireless and Fiber-IVLLC Convergence System with a Dual-Polarization Modulation Scheme and an MZM-OEO-Based BLS

A bidirectional fiber-wireless and fiber-invisible laser light communication (IVLLC) convergence system that adopts a dual-polarization modulation scheme and a Mach–Zehnder modulator (MZM)-optoelectronic oscillator (OEO)-based broadband light source (BLS) for hybrid cable television (CATV)/microwave (MW)/millimeter-wave (MMW)/baseband signal transmission is proposed and experimentally demonstrated. The MZM employed in the MZM-OEO is operated at the minimum transmission point, which results in the format of optical carrier suppression for the y -axis component of the light. Using a dual-polarization modulation scheme, the optical carrier modulated with CATV signal ( x -polarization) and the optical sidebands modulated with MW and MMW data signals ( y -polarization) are separated and polarized orthogonally automatically. Through an in-depth observation, good carrier-to-noise ratio, composite second-order, composite triple-beat, and bit error rate performances are obtained over a 40-km single-mode fiber and a 10-m RF/100-m optical wireless transport. Such a bidirectional fiber-wireless and fiber-IVLLC convergence system is a notable option; it would be attractive for providing broadband heterogeneous services such as CATV, Internet, and big data services.

A tunable and wideband microwave photonic phase shifter based on dual-polarization modulator

A microwave photonic phase shifter based on dual-polarization Mach-Zehnder modulator (DPol-MZM) is proposed and experimentally demonstrated in this paper. A polarization multiplexed double sideband (DSB) signal is produced by a DPol-MZM. An optical bandpass filter (OBPF) follows after the DPol-MZM to filter out the optical carrier and one sideband. The polarization multiplexed signal is converted into a linear polarization light by a polarizer (Pol), and then beat at a photodiode (PD) to obtain the phase shifted signal. Experiments are carried out, and a continuous phase shift from −180° to 180° over a wide microwave frequency range of 10–33GHz can be achieved by changing the polarization state using a polarization controller (PC). We also studied the spurious free dynamic range (SFDR) in the experiments. The features of this proposed phase shifter are large operation bandwidth, full-range 360° phase shift, and simple structure.

Photonic generation of frequency-sextupled microwave signal based on dual-polarization modulation without an optical filter

Frequency-sextupled microwave signal generation based on dual-polarization modulation using an electro-optic dual-parallel polarization modulator (DPPolM) without an optical filter is proposed. From a theoretical analysis, the frequency-sextupled microwave signal can be obtained by properly adjusting the polarization directions of the modulated optical signals, the powers and the phases of the microwave drive signals applied to the DPPolM. Simulation results show that a 24GHz microwave signal with an optical sideband suppression ratio (OSSR) exceeding 31dB and a radio frequency spurious suppression ratio (RFSSR) higher than 25dB is generated from a 4GHz microwave drive signal, which match well with the theoretical analysis. Furthermore, it is also proved to be valid that even if the microwave drive voltage, the phase difference, and the polarization direction of light wave deviate from the ideal values to a certain degree, the performance of the generated frequency-sextupled microwave signal is still acceptable.

Triangular Pulse Generation by Polarization Multiplexed Optoelectronic Oscillator

A novel triangular pulse generator is proposed based on a polarization multiplexed optoelectronic oscillator (OEO). Employing a dual-polarization modulator, the proposed OEO can simultaneously oscillate at two frequencies of $f$ and $3f$ along the two orthogonal polarizations of the same optical carrier. Thanks to the harmonic injection coupling between the two OEO oscillations, the generated two signals have an exact frequency ratio of 1:3 and can be tuned to be in phase with each other. By properly setting the amplitudes of the two signals, a triangular pulse train can be generated. The generation of a 4.44-GHz triangular pulse train is experimentally demonstrated. A very clean electrical spectrum incorporating the 4.44- and 13.32-GHz components is obtained, and the two tones have good phase noises of −100.6 dBc/Hz at 10 kHz and −99.2 dBc/Hz at 10 kHz, respectively. The generated triangular waveform is very close to an ideal waveform, and the root-mean-square error between the generated and the ideal waveforms is $5.145\times 10^{-4}$ .

Dynamic Range Improvement for an Analog Photonic Link Using an Integrated Electro-Optic Dual-Polarization Modulator

A novel analog photonic link with enhanced spurious-free dynamic range (SFDR) based on an integrated electro-optic dual-polarization modulator is presented and demonstrated. The dual-polarization modulator, which consists of a polarization beam splitter, a polarization beam combiner, and two z-cut LiNbO 3 MZMs, can achieve complementary intensity modulation along the orthogonal polarization directions with different modulation indexes. By properly adjusting the power relationship of the orthogonal polarization directions, two third-order intermodulation distortions (IMD3) have equal intensity and opposite phase and cancel each other out. Combined with a low-biasing technique to reduce the noise power, the SFDR of the link can be further improved. A theoretical analysis is presented and validated by a simulation. The IMD3 can be suppressed by 30.6 dB, giving an improvement in SFDR of about 22 dB compared with a conventional optical double-sideband modulation link.

Filter-less frequency-doubling microwave signal generator with tunable phase shift

A prototype for frequency-doubling microwave signal generator with tunable phase shift based on a filter-less architecture is proposed and analyzed. In the proposal, one dual parallel polarization modulator is used as the key component to generate two ±1st order sidebands along the orthogonal polarization directions with suppressed carrier. Then the polarization states of the two sidebands are aligned with the principal axes of an electro-optical phase modulator (EOPM). Tunable phase shift is implemented by controlling the direct current voltage applied to the EOPM. Without using any filters or wavelength-dependent components, the system possesses good frequency tunability and it can be applied to multi-wavelength operation. Taking advantage of the ability of frequency multiplication, the frequency tuning range can be wider than the operation bandwidth of the modulator. By theoretical analyses and simulated verifications, a frequency-doubling microwave signal ranging from 22 to 40GHz with full range phase shift is achieved.

Phase-coded microwave signal generation based on a single electro-optical modulator and its application in accurate distance measurement.

A novel scheme for photonic generation of a phase-coded microwave signal is proposed and its application in one-dimension distance measurement is demonstrated. The proposed signal generator has a simple and compact structure based on a single dual-polarization modulator. Besides, the generated phase-coded signal is stable and free from the DC and low-frequency backgrounds. An experiment is carried out. A 2 Gb/s phase-coded signal at 20 GHz is successfully generated, and the recovered phase information agrees well with the input 13-bit Barker code. To further investigate the performance of the proposed signal generator, its application in one-dimension distance measurement is demonstrated. The measurement accuracy is less than 1.7 centimeters within a measurement range of ~2 meters. The experimental results can verify the feasibility of the proposed phase-coded microwave signal generator and also provide strong evidence to support its practical applications.

双偏振调制大范围高分辨率瞬时微波频率测量

双偏振调制大范围高分辨率瞬时微波频率测量

An improved multiplier-free feed-forward carrier phase estimation for dual-polarization QPSK modulation format

An improved multiplier-free feed-forward carrier phase estimation algorithm is proposed for dual-polarization quadrature-phase-shift-keying (DP-QPSK) with coherent detection. The bit error rate (BER) performance, block length effect and linewidth tolerance of the proposed algorithm are evaluated for a 112 Gbit/s DP-QPSK system. A linewidth symbol duration product of 2.9×10−4 is demonstrated for 1 dB optical signal-to-noise-ratio (OSNR) penalty at BER of 10−3 for the proposed algorithm. The hardware complexity of the proposed multiplier-free algorithm is demonstrated to be much lower than that of the 4th power algorithm.

Transmission of Spectral Efficient Super-Channels Using All-Optical OFDM and Digital Coherent Receiver Technologies

A 1.5 Tb/s super-channel is generated using all-optical orthogonal frequency-division multiplexing (OFDM) and dual-polarization 16QAM modulation without guard interval. We investigated the effects of DSP oversampling and receiver bandwidth using experimental results and numerical simulations to evaluate our receiver design. The super-channel is transmitted over 1200 km of standard single-mode fiber on existing 100 GbE network using only 200 GHz of optical bandwidth and detected using digital coherent receiver, achieving a spectral efficiency of 7 bit/s/Hz the highest reported to date for all-optical OFDM techniques.

Modulator Bias and Optical Power Control of Optical Complex E-Field Modulators

We describe novel techniques for closed-loop control of inner and outer Mach-Zehnder (MZ) biases in a dual parallel MZ (DPMZ) optical modulator. We also present a new technique based on modulator bias dithers to monitor the optical power contribution of each RF data path. The latter is demonstrated in an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> power balance control loop. We show that the new control methods are extremely robust in presence of modulator non-idealities, such as finite extinction ratios and non-zero chirp. We also demonstrate these techniques to be largely independent of RF drive waveform characteristics. Mathematical derivations of control transfer curves are provided. These are supported by simulation and measurement results. Additionally, we present a simple technique for polarization power balance in a dual-polarization modulation format. Finally, we discuss some practical details related to the implementation of the control loops described in this work.

Compact, Low-Cost, Surface-Mount Active Antenna

A very simple surface-mount dual-polarized active antenna module consists of up/down converter ICs mounted directly on top of a patch antenna radiator. By incorporating ICs on the patch surface, the design saves space, an important feature in phased arrays where wide scanning range requires half-wave spacing. The module is fabricated on a soft substrate and contains only one dielectric layer, no cutouts, and no blind vias. Measurements of both single- and dual-polarized 10-GHz prototypes show a normal copolarized radiation pattern and less than - 12 dB of cross polarization.

The Hertz/VPM polarimeter: design and first light observations

We present first results of Hertz/VPM, the first submillimeter polarimeter employing the dual Variable-delay Polarization Modulator (dual-VPM). This device differs from previously used polarization modulators in that it operates in translation, rather than mechanical rotation. We discuss the basic theory behind this device and its potential advantages over the commonly used half-wave plate. The dual-VPM was tested both at the Submillimeter Telescope Observatory and in the laboratory. In each case we present a detailed description of the setup. We discovered that properties of the VPM wire grids (diameter and spacing) caused behavior that differs from theoretical predictions for ideal wire grid performance. By modifying the polarimeter settings to compensate for this behavior, we found that the dual-VPM system is robust, operating with high efficiency and low instrumental polarization. This device is well suited for air- and space-borne applications.

Reduction of linear birefringence in vibrational circular dichroism measurement: use of a rotating half-wave plate

A new method has been developed to suppress the effects of linear birefringence (LB) associated with sample cells in the measurement of vibrational circular dichroism (VCD) spectra by adding a rotating half-wave plate (RHWP) to the optical train. The method functions in combination with the previously developed dual polarization modulation (DPM) technique and involves placing the RHWP after the second photo-elastic modulator (PEM) of the DPM setup. In the DPM setup without the RHWP, all sources of LB terms are first reduced and then further cancelled by real time electronic subtraction, except for one remaining LB term associated with sample cell. Not infrequently, however, this remaining source of LB between the two PEMs with axes at 45° relative to the stress axes of the PEMs leads to noticeable deviations of the VCD baseline that cannot be eliminated. The new method described here depends on the use of an achromatic half-wave plate which is currently available in the near-infrared region with a low-frequency cut off near 2,000 cm−1. It is demonstrated theoretically, and experimentally in the CH stretching region, that the addition of a RHWP eliminates this last remaining source of LB from the VCD measurement.