Optimization of an Externally Modulated RF Photonic Link

The noise figure and sub-octave spurious-free dynamic range of a carrier-suppressed analog RF photonic link are examined. Expressions for noise figure and dynamic range are derived as a function of the modulator bias angle. A closed form expression for the bias angle that optimizes link noise figure and spurious-free dynamic range is also derived. Experimental results are presented and shown to agree with calculations. These experimental results include some of the lowest noise figure and highest dynamic range results published to date for an RF photonic link incorporating a standard Mach-Zehnder modulator: 6 dB and 122 dB·Hz^2/3, respectively.     

Microwave Photonic Link with Carrier Suppression for Increased Dynamic Range

Theoretical analysis and experimental investigation of microwave photonic links with bias-shifted Mach-Zehnder modulators are presented. An optical amplifier is used to increase link gain and reduce noise figure. The combination of modulator bias shift away from quadrature and optical amplification reduces the link noise figure by more than 15 dB. For modulation frequencies from 2 to 18 GHz, the third-order limited spurious-free dynamic range (SFDR3) of these links is greater than 120 dB, normalized to a 1-Hz bandwidth. Conventional links based on Mach-Zehnder modulators are limited to SFDR3 values of approximately 110 dB, normalized to a 1-Hz bandwidth. This level of performance is achieved without electronic or optical linearization.     

基于双平行马赫-曾德尔调制器的大动态范围微波光子下变频方法

为了提高微波光子下变频链路的性能,提出了基于集成双平行马赫-曾德尔调制器的微波光子下变频方法.通过理论推导和数值仿真分析了系统的增益和无杂散动态范围,实验搭建了基于双平行马赫-曾德尔调制器的下变频链路,控制直流偏置电压使双平行马赫-曾德尔调制器工作在高载波抑制的双边带调制模式,并对链路进行了性能测试.实验结果表明:该下变频链路的增益为7.43 d B,无杂散动态范围达到了110.85 d B/Hz2/3,工作频段可覆盖5—18 GHz的宽频范围.基于双平行马赫-曾德尔调制器的下变频方法可优化设计输出频谱,系统结构简单、易于实现,为微波光子下变频链路提供了有效的解决方案.     

Full-band direct-conversion receiver with enhanced port isolation and I/Q phase balance using microwave photonic I/Q mixer

A full-band direct-conversion receiver using a microwave photonic in-phase and quadrature(I/Q) mixer is proposed and experimentally evaluated in terms of radio frequency(RF) range, port isolation, phase imbalance,conversion gain, noise figure, spurious-free dynamic range, and error vector magnitude. The proposed microwave photonic I/Q mixer shows significant advantages in local oscillator leakage and I/Q phase imbalance over entire RF bands, which are recognized as major drawbacks of conventional direct-conversion receivers.     

Performance of analog optical links employing fiber Raman amplifiers

We present the characterization of an analog optical link employing external modulation and optical carrier in the C-band using a fiber Raman amplifier (FRA). The figures of merit gain and noise figure were characterized from 1 to 9 GHz, whereas the spurious-free dynamic range was measured and compared for both setups for frequencies from 2 to 9 GHz, all with and without the Raman amplifier. Experimental results demonstrate that FRA can simultaneously increase the spurious-free dynamic range, the analog gain and decrease the analog noise figure when compared to the same configuration without optical amplifier.     

两路输入前置光放大星间微波光子链路优化

考虑到星间微波光子链路传输损耗大且多路微波信号之间交调干扰严重,利用前置光放大来提高链路的信号噪声失真比RSNDR。建立了两路输入前置光放大星间微波光子链路模型,推导出了RSNDR的解析表达式。通过优化马赫-曾德尔调制器的直流偏置相移,使得在给定输入射频信号功率条件下RSNDR最大,并进一步分析了前置光放大器参数对最优直流偏置相移和RSNDR的影响。仿真结果表明,前置光放大改变了影响RSNDR的主要因素,使信号放大的倍数大于噪声和三阶交调(IM3)放大的倍数,从而提高了链路的RSNDR。当前置光放大器增益为20dB、噪声系数为3dB时,最优的RSNDR比不加前置光放大器时提高24dB。前置光放大器增益和噪声系数对最优的RSNDR影响很大,而对最优的直流偏置相移几乎无影响。     

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.     

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.     

Novel model of FM-noise conversion in a UMZI using RF external phase modulation of lasers: Theoretical and experimental results

In this paper, we propose and demonstrate a new and original model for theoretical calculation and experimental measurement of the noise power spectral density (NPSD) in phase-modulated optical links. The phase modulation is operated in the RF frequency range by an external phase modulator. The NPSD is derived for the first time in interferometric systems, by considering all effects such as the 1/f FM noise of the laser and white noise applied to light from a 1550 nm DFB laser, with phase modulation. The results show for the first time the influence of the phase modulation index, modulation frequency and interferometric delay in the phase-to-intensity noise conversion. The experimental and simulation results of conversion of FM-noise to intensity noise in an optical link by considering the external RF phase modulation are shown with good agreement.     

Linearized analog photonic links based on a dual-parallel polarization modulator

A linearized analog photonic link (APL) is proposed based on an integratable electro-optic dual-parallel polarization modulator (DPPolM), which consists of two polarization beam splitters and two polarization modulators (PolMs). Theoretical analysis shows that the APL is potentially free from the third-order nonlinear distortion if a polarization controller placed before the DPPolM is carefully adjusted. A proof-of-concept experiment is carried out. A reduction of the third-order intermodulation components as high as 40 dB and an improvement of the spurious-free dynamic range as large as 15.5 dB is achieved as compared with a single PolM-based link. The DPPolM-based APL is simple, compact, and power efficient since it requires only one laser, one modulator, and one photodetector.     

基于侧向PN结和交趾型PN结的硅基Mach-Zehnder调制器的二阶谐波失真特性

高线性度的电光调制器是构建微波光子链路的核心器件。硅光子调制器利用PN结的载流子色散效应实现微波信号对光波的调制,基于不同结构PN结的调制器有不同的非线性特性。本文采用二阶无杂散动态范围表征二阶谐波失真度,实验研究了采用侧向PN结和交趾型PN结所构成的Mach-Zehnder(MZ)调制器的二阶谐波失真特性。基于侧向PN结和交趾型PN结的MZ调制器的二阶无杂散动态范围为分别为85.11dB·Hz~(1/2)、78.44 dB·Hz~(1/2),表明基于侧向PN结的MZ调制器具有更好的线性度。     

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.     

Compensation of dispersion-induced power fading for highly linear radio-over-fiber link using carrier phase-shifted double sideband modulation

A carrier phase-shifted (CPS) double sideband (DSB) modulation technique in radio-over-fiber (RoF) system is proposed and experimentally demonstrated. By tuning the biases in a single-drive dual parallel Mach-Zehnder modulator (SD-DPMZM), the optical carrier in the DSB spectrum acquires additional phase shift. The transmittance response of a dispersive RoF link is thus being controlled and shifted in the frequency domain. Experiments successfully turned the maximum transmission frequency to 10?GHz and 15?GHz for both 25 and 39?km fiber links. This is also a highly linear scheme, of which a spurious-free dynamic range (SFDR) of 111.3?dB·Hz^2/3 is experimentally obtained.     

Optoelectronic Oscillator Based on Polarization Modulation

Abstract

A polarization modulator together with a polarizer can implement phase modulation, intensity modulation with tunable chirp, and frequency-doubling intensity modulation. If an optical filter is incorporated, frequency-quadrupling and frequency-sextupling intensity modulations and a microwave photonic phase shifter can also be realized. By using a polarization modulator to replace the intensity modulator in an optoelectronic oscillator, various new features are enabled. In this article, an analytical model for the polarization modulator-based systems is established. The recent development in employing polarization modulators for constructing optoelectronic oscillators is discussed. The emerging applications enabled by the polarization modulator-based optoelectronic oscillators and the possible future development are also discussed.     

Optically referenced broadband electronic synthesizer with 15 digits of resolution

Fundamental science, as well as all communications and navigation systems, are heavily reliant on the phase, timing, and synchronization provided by low‐noise and agile frequency sources. Although research into varied photonic and electronic schemes have strived to improve upon the spectral purity of microwave and millimeter‐wave signals, the reliance on conventional electronic synthesis for tuning has resulted in limited progress in broadband sources. Using a digital‐photonic synthesizer architecture that derives its time‐base from a high‐stability optical reference cavity, we generate frequency‐agile and wideband microwave signals with exceptional dynamic range and with a fractional frequency instability of 1 × 10⁻¹⁵ at 1 s. The presented architecture demonstrates digitally controlled, user defined and broadband frequency tuning from RF to 100 GHz with orders‐of‐magnitude improvement in noise performance over room‐temperature electronic wide‐bandwidth synthesis schemes.

     

Designing High Dynamic Range Microwave Photonic Links for Radio Applications

A tutorial review to design high-performance microwave photonic links is presented. The link performance is analyzed in detail in terms of the link gain, noise figure, and dynamic range. The two-port microwave network is used to model fiber optic links, which takes full advantage of microwave circuit analysis. We have also examined and compared several kinds of noise suppression techniques on the basis of balanced and/or carrier filtering schemes to achieve maximum dynamic range.     

星间微波光子链路调制方式的优化

针对外调制星间微波光子链路输出信噪比优化问题,建立了基于双电极马赫 曾德尔调制器的强度调制直接探测星间微波光子链路模型,通过优化调制器调制方式来提高链路性能。用数值模拟方法得到了单边带、双边带和推挽式3种调制方式下链路输出信噪比,利用曲面投影法求得了最优调制方式时一定信噪比要求下发射端所需最小光放大器增益和对应的调制器直流偏置相位。结果表明:相同输入射频信号功率和发射光功率情况下,双边带调制输出信噪比比单边带调制高3 dB,低直流偏置相位推挽调制可以进一步优化输出信噪比。输入射频信号功率为-20 dBm,输出信噪比为17.3 dB时,所需最小光放大器增益为43.9 dB,对应的直流偏置相位为0.87。     

A tunable and reconfigurable microwave photonic filter based on two cascaded modulators and a dispersive medium

A novel tunable and reconfigurable microwave photonic filter based on two cascaded modulators and a dispersive medium is proposed, theoretically discussed and experimentally demonstrated. A single-wavelength LD and a modulator (either a Mach-Zehnder modulator or a phase modulator which can avoid the dc bias drift problem) are used to obtain a multi-wavelength optical source. By adjusting the modulation frequency and the bias voltage on the modulators, the wavelength spacing and the relative amplitude of the optical tones change, thus making the filter tunable and reconfigurable. The experimental results show that the proposed filters have good tunability and reconfigurability and the mainlobe-to-sidelobe ratio of around 25 dB is achieved.     

Polarization-modulated analog photonic link with compensation of the dispersion-induced power fading

A novel integrable modulator consisting of a polarization modulator and a polarizer is proposed for constructing a high-performance analog photonic link. By adjusting a polarization controller placed before the modulator, both amplitude modulation and phase modulation with adjustable ratio between them are implemented. This feature is used to shift the peak of the frequency response of a dispersive link to any desired frequency, so the dispersion-induced power fading around the frequency is compensated. A proof-of-concept experiment is performed. The compensation of the dispersion-induced power fading in the proposed analog photonic link increases the spur-free dynamic range as large as 12.5 dB.     

EAM-SOA millimeter-wave frequency up-converter for radio-over-fiber applications

We present an optical scheme for photonic frequency up-conversion at the millimeter-wave bands based on Semiconductor Optical Amplifier. The proposed scheme modulates the bias current with the Intermediate Frequency in order to achieve frequency mixing of an incoming optical signal modulated with the Local Oscillator. Theory indicates that the proposed scheme supports data bandwidths in the tens of GHz for LO values above 10 GHz. This scheme allows for photonic integration of the considered optical devices. A laboratory demonstration of the scheme for up-conversion to the 40 GHz band, using narrow-band IF signals, showed relatively low thresholds for the optical input power and bias current level to achieve error free operation: − 14.5 dBm 100 mA for a 64-QAM signal. Spurious-Free Dynamic Range showed an acceptable performance, with a linearity about 52.5 dB·Hz^2/3 for an optical input power of − 6 dBm.