Microwave Photonic Up- and Down-Converter with Tunable Phase Shift Based on an Integrated Dual-Polarization Dual-Parallel Mach–Zehnder Modulator without Optically Filtering

ABSTRACT

In this paper, we propose and numerically simulate a microwave photonic phase-tunable frequency converter (MPPTFC) without optically filtering to realize both frequency up- and down-conversion and a full 360° phase-shift for the microwave signal based on an integrated dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). In the proposed scheme, both microwave RF signal and frequency-tunable local oscillator (LO) are modulated on the lightwave by single-sideband carrier suppression (SSB-CS) modulation to generate optical orthogonally polarized optical tones carrying RF signal with up- or down-converted frequency. A PolM that can support lightwave modulation with opposite modulation indices in transverse electric (TE) and transverse magnetic (TM) modes is used to introduce a phase difference between the two modes. Then the orthogonally polarized optical tones are aligned into a single polarized state by a polarizer (Pol) and detected by a photodiode (PD), a frequency-converted and phase-shifted microwave signal can be obtained. Simulation results demonstrate that the proposed MPPTFC can up-/down-convert the microwave signal with a tunable frequency shift of LO frequency and realize a 360° continuously tunable phase shift via the DC bias voltage of the PolM simultaneously.     

Microwave Photonic Phase Shifter Based on an Integrated Dual-polarization Dual-parallel Mach-Zehnder Modulator without Optical Filter

ABSTRACT

A frequency-doubled microwave photonic phase shifter (MPPS) without optical filter is proposed. The MPPS is based on an integrated dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM with a 90° polarization rotator in one arm is used to generate an optical carrier suppressed double sideband (OCS-DSB) signal with orthogonal polarization, and the PolM with two modes opposite phase modulation is used to introduce the optical phase shift between the two orthogonally polarized tones. Simulations show that the MPPS can realize a continuously tunable phase shift of 360° with only one DC bias voltage, and is not sensitive to the optical carrier wavelength and microwave signal frequency since no optical filter is used.     

Generation of an arbitrary chirped microwave waveform with high time-bandwidth product for increasing range resolution of RADAR by using photonic technique

An approach for photonic generation of an arbitrary chirped microwave waveform with an increased time-bandwidth product (TBWP) is proposed and experimentally demonstrated. In the proposed model, light from the mode locked laser is splitted into two parts by using 1 × 2 power splitter: one is sent to linearly chirped fiber Bragg grating (LCFBG) through circulator and the other is time delayed by fiber delay line. The optical pulse in upper arm is time stretched by the LCFBG. Meanwhile, the optical pulse in lower arm experiences a time delay and then stretched by the dispersive single mode fiber. Temporal interference pattern is generated with an increasing or decreasing free spectral range by combination of two time-stretched optical pulses. Finally, the temporal interference pattern which is obtained at the output of optical coupler is transformed into an arbitrary chirped microwave waveform by using a photo-detector. The main advantage of this proposed model is high TBWP in the range of 750–1000 which ultimately results in an increased range resolution of radio detection and ranging.     

I/Q intensity-demodulation analog photonic link based on polarization modulator

We experimentally investigate a high-linearity analog photonic link based on polarization-modulation in-phase/quadrature (I/Q) intensity-demodulation. In the proposed system, a light wave with its polarization direction oriented at an angle of 45° with respect to the principal axis of the polarization modulator (PolM) is polarization modulated by a drive signal. In the receiver, the polarization-modulated signal is split into two paths using a 50:50 optical coupler (OC). In each path, a polarization beam splitter (PBS) is connected to the PolM via a polarization controller (PC) to realize the in-phase and quadrature signal, respectively. Thanks to the polarization-modulation to intensity-modulation conversion, the fluctuation of the optical phase noise has no impact on the coherent signals. In addition, the use of a single PolM allows the link avoids the matching requirements of dual modulator schemes. The linearization leads to suppression of the third-order intermodulation (IMD3) by more than 40 dB, compared to the quadrature signal. Experimental results show that the link gain is -11.5 dB, noise figure is 26.5 dB, and the third-order limited spurious free dynamic range (SFDR) is 124 dB in a 1 Hz bandwidth.     

A photonic scheme for the generation of dual linear chirp microwave waveform based on the external modulation technique and its airborne application

Due to high frequency and large time bandwidth product; photonic generation and processing of arbitrary microwave waveforms has been an interesting topic in recent time. Here, a relatively new photonic technique has been proposed for the generation of a dual linear chirp microwave waveform in Ku-band. In this method two single drive Mach–Zehnder Modulators are cascaded at minimum transmission point and in push–pull mode. Theoretical analysis and simulation are developed by giving a complete mathematical model. As the result of this methodology, a dual linear chirp microwave waveform in Ku-band with relatively large bandwidth is generated. Comparative analysis is done in the present cascading technique with dual parallel Mach–Zehnder Modulator (DPMZM) technique. Range-Doppler coupling of the radar system has been investigated with the help of an ambiguity function diagram of the generated waveform. Results have analyzed through MATLAB simulation and verified by experimental results.     

Switchable instantaneous frequency measurement by optical power monitoring based on DP-QPSK modulator

We propose and analyze an instantaneous frequency measurement system by using optical power monitoring technique with improved resolution. The primary component adopted in the proposal is a dual-polarization quadrature phase shift keying (DP-QPSK) modulator which is used to modulate the microwave signal that has a designed time delay and phase shifting. The generated optical signal is sent to polarization beam splitter (PBS) in DP-QPSK modulator. Owing to the complementary transmission nature of polarization interference introduced by PBS, the frequency information is converted into the optical power and the relationship between the amplitude comparison function (ACF) and microwave frequency to be measured is established. Thus, the frequency of the microwave signal can be easily measured through monitoring the optical powers of the two output ports of the PBS. Furthermore, by adjusting the direct current (DC) biases of the DP-QPSK modulator instead of changing the electrical delay, the measurement range and resolution can be switched. In this paper, the basic principle of the instantaneous frequency measurement system is derived in detail, and simulation has been performed to investigate the resolution, the measurement range, and the influence of imperfection devices. The proposed scheme is wavelength-independent and its measurement range is switchable, which can avoid the laser wavelength drifting problem and thus greatly increasing the system flexibility.     

A tunable and switchable single-longitudinal-mode dual-wavelength fiber laser incorporating a reconfigurable dual-pass Mach-Zehnder interferometer and its application in microwave generation

A tunable and switchable single-longitudinal-mode (SLM) dual-wavelength fiber laser incorporating a reconfigurable dual-pass Mach-Zehnder interferometer (MZI) filter was proposed and demonstrated, which can be applied in microwave generation. By incorporating a high extinction ratio (ER) dual-pass MZI into an erbium-doped fiber ring cavity, SLM dual-wavelength lasing can be achieved even using a MZI with relatively little free spectrum range (FSR), and by beating the two wavelengths at a photodetector, a 9.76 GHz microwave signal with a 3-dB bandwidth of less than 10 kHz is obtained. Moreover, by direct linking the two outputs of the MZI, the high ER dual-pass MZI is easily reconfigured as a half FSR dual-pass MZI. Using this structure, switchable SLM dual-wavelength lasing can be conveniently realized.     

Optoelectronic oscillator using a LiNbO3 phase modulator for self-oscillating frequency comb generation

Optical frequency comb generation by using a novel optoelectronic oscillator (OEO) is proposed and demonstrated with the emphasis placed on self-oscillating operation. In the OEO, a wideband LiNbO3 phase modulator is driven with a large-amplitude radio-frequency (RF) feedback signal to generate a deeply phase-modulated light wave; accordingly, an optical frequency comb with a bandwidth greater than the RF signal is generated by self-oscillation. Although it generates multifrequency components, the OEO exhibits characteristics of a single-mode oscillator. Its operation is stable and self-starting. An optical frequency comb with a 120 GHz bandwidth and 9.95 GHz frequency spacing was successfully generated by self-oscillation at a single frequency.     

基于互逆光纤色散的微波光子雷达系统设计和实现

提出一种基于互逆光纤色散的微波光子雷达系统设计方案,既可以产生宽带线性调频信号,又可以实现线性调频信号的光域脉冲压缩.在发射端利用互逆色散光纤产生线性调频信号.在接收端,雷达回波信号通过马赫-曾德调制器调制到预啁啾的光信号上,然后经过色散光纤的进一步色散.最终在探测器端可以得到目标回波信号脉冲压缩后的结果.该方案无需脉冲压缩过程中数字化和离线处理,且具有脉冲压缩比的调谐作用.理论、数值仿真和实验证明了该设计方案能有效进行线性调频信号的光域脉冲压缩.实验产生了C波段下时宽1.2ns,带宽3.2GHz的线性调频信号,并通过互逆色散光纤将该信号压缩到了0.09ns,脉冲压缩比达13.3.     

Photonic instantaneous measurement of microwave frequency using fiber Bragg grating

A photonic approach to realizing instantaneous measurement of microwave frequency based on optical monitoring using a fiber Bragg grating (FBG) is proposed and demonstrated. In the approach, a frequency-unknown microwave signal is modulated on an optical carrier in a Mach-Zehnder modulator biased at the minimum transmission point. After detecting the transmission and reflection optical powers at the output of the FBG, the microwave frequency can be determined according to the value of transmission-to-reflection power ratio, due to the fixed relationship between the microwave frequency and the power ratio. A proof-of-concept experiment has been performed, which demonstrates that a measurement resolution of ±0.08 GHz over a 10 GHz measurement bandwidth is achieved. The measurement performance in terms of resolution is better than previously reported results.     

Reconfigurable photonic generation of microwave hybrid frequency/phase shift keying signals

A photonic approach for the generation of microwave hybrid frequency/phase shift keying (FSK/PSK) signal based on an integrated polarization division multiplexing dual-parallel Mach–Zehnder modulator (PDM-DPMZM) is proposed and demonstrated. In the scheme, the polarization modulator is employed to modulate the linearly polarized lightwave to generate an optical polarization-shift keying (PolSK) signal. Then the PolSK signal is sent to the PDM-DPMZM via a polarization controller to generate optical PSK signal. After photo-detection, a microwave hybrid FSK/PSK signal can be obtained. Simulations are conducted to verify the proposed scheme. As bit rate is set to 1 Gbit/s, a hybrid FSK/PSK signal with frequency of 10/15 GHz and phase shift of\(\pi\)is successfully demonstrated. Hybrid signals with 2-Git/s frequency shift and 1-Git/s phase shift are also implemented. The compression ratio of the generated signal is 25.5 and the main-to-sidelobe ratio is 11.2 dB. The generations of ASK, PSK and FSK signals are discussed, and the impact of the polarization extinction ratio is also analyzed.     

Optical Microwave and Millimeter Generation by Using Birefringent Fiber FP Cavity with Pulse Laser Injection

A novel optical microwave and millimeter generation by using single mode fiber FP cavity (SMFFPC) with pulse laser injection is proposed and experimentally demonstrated. The frequency of output signal is determined by the birefringence degree of the SMFFPC, a general relationship between output signal frequency of SMFFPC and birefringence degree of single mode fiber is derived. The proof of concept device consists of a light source, a polarizer controller, a modulator, a RF generator, a single mode fiber Fabry-Perot cavity, a strain inspector, an erbium doped fiber amplifier, a filter, a polarizer, and a digital communication analyzer. The results demonstrate the new concept of optical microwave and millimeter generation and the technical feasibility.     

Microwave Frequency Quadrupling Based on Distributed Feedback Laser and a Single Intensity Modulator

In this article, we have proposed and experimentally demonstrated a directly modulated distributed feedback laser (DFB-LD) to generate microwave and millimeter-wave signals. The proposed scheme uses DFB-LD and intensity modulator (IM) biased at null point. A radio frequency (RF) signal from a signal generator is split into two branches and one branch directly modulates the DFB-LD, while the other branch drives the IM. Two second-order sidebands separated by four times the frequency of the input RF signal are generated. Experimental results indicated that we can generate a four-fold microwave signal with a good optical signal to noise ratio.     

Photonic instantaneous microwave frequency measurement based on two different phase modulation to intensity modulation conversions

A novel photonic technique for instantaneous frequency measurement of microwave signal based on phase modulation to intensity modulation conversion is proposed and demonstrated. In the proposed system, an optical carrier is modulated by a microwave signal with its frequency to be measured through a phase modulator. The phase-modulated optical signal is then converted to intensity-modulated signals in two independent paths using a dispersive media and a frequency discriminator respectively. Since the dependence of the received microwave power on the input microwave frequency in the two paths differs, the microwave power ratio between the two paths can be used to uniquely determine the microwave frequency. The major advantages of the approach lie in that only one laser source and the bias-free phase modulator is employed in the system, which improves the stability of the system. Experimental demonstrations of the frequency measurement based on the proposed approach are presented.     

Frequency quadrupling using an integrated Mach–Zehnder modulator with four arms

In this paper, a novel technique to realize frequency quadrupling in the radio over fiber system is proposed. The frequency quadrupling is achieved by using an integrated Mach–Zehnder modulator (MZM) consisting of a 1 × 4 multimode interference (MMI) coupler and four optical phase modulator arms. Due to the inherent optical splitting ratio and phase relations between the outputs of the MMI coupler, the optical harmonics at + 1 order and ? 3 order are generated corresponding to four times frequency of the microwave drive signal, only by setting the DC bias voltage of the main MZM at the minimum transmission point. That leads to the integrated MZM with reduced complexity compared with the conventional dual-parallel MZM. The effect of the nonideal integrated MZM, including the splitting imbalance and the bias drift, on all the sidebands is also analyzed theoretically. The following simulation results show that the slight deviation of the ideal values would not cause great degradation of the generated optical millimeter-wave signal.     

Reversible waveform conversion between microwave and optical fields in a hybrid opto-electromechanical system

We present a scheme of reversible waveform conversion between microwave and optical fields in the hybrid opto-electromechanical system. As an intermediate interface, nanomechanical resonator optomechanically couples both optomechanical cavities in the optical and microwave frequency domains. We find the double-optomechanically induced transparency and achieve coherent signal waveform bi-directional transfer between microwave and optical fields based on quantum interference. In addition, we give an analytical expression of one-to-one correspondence between the microwave field and the optical output field, which intuitively shows the reversible waveform conversion relationship. In particular, by numerical simulations and approximate expression, we demonstrate the conversion effects of the three waveforms and discuss the bi-directional conversion efficiency and the bandwidth. such a hybrid opto- and electro-mechanical device has significant potential functions for electro-optic modulation and waveform conversion of quantum microwave-optical field in optical communications and further quantum networks.     

High carrier suppression double sideband modulation using polarization state rotation filter and optical external modulator

We propose a high carrier suppression double sideband modulation technique using a Mach-Zehnder modulator (MZM) and an integrated polarization state rotation filter (PSRF), which is designed to improve the carrier suppression ratio. With the functions of MZM and PSRF, about 30 dB carrier suppression ratio relative to first-order sidebands is demonstrated. Moreover, we demonstrate the optical generation of microwave/millimeter-wave signals by beating the carrier suppressed double sideband (DSB-SC) lightwave signals. The experimental results show that the improvement of carrier suppression ratio with PSRF can effectively cancel the modulating RF frequency component. A tunable and high purity microwave signal, which is limited by the bandwidth of MZM and photodetector (PD), is obtained, and it does not suffer from obvious phase noise degradation with 25 km transmission.     

应用HFSS和Designer对电光调制器的协同仿真

应用ANSYS公司的HFSS和Designer对一种内嵌共面波导电极结构的聚合物电光调制器进行了协同仿真,设计出了带宽为56 GHz的聚合物电光调制器.通过对光波有效折射率和微波有效折射率的优化,实现了速度匹配.同时利用协同仿真方法对电极进行了优化设计,实现了阻抗匹配并降低了微波损耗.结果表明应用协同仿真方法可以提高计...     

Switchable microwave photonic filter using a phase modulator and a silicon-on-insulator micro-ring resonator

A switchable microwave photonic filter(MPF) using a phase modulator(PM) and a silicon-on-insulator microring resonator(MRR) is proposed and demonstrated. By adjusting the polarization controller between the PM and the MRR, the filtering function of the MPF can be switched between a band-stop filter and a band-pass filter. In a proof-of-concept experiment, an MPF with a rejection ratio of 30 dB(or 15 dB) for the band-stop(or band-pass) response and a frequency tuning range from 9.6 to 20.5 GHz is achieved.     

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.