Microwave Photonic Phase Shifter Research Articles

Filterless Frequency Octupling Microwave Photonic Phase Shifter Based on Cascaded Mach–Zehnder Modulators

ABSTRACT In this paper, we propose a microwave photonic phase shifter (MPPS) without optical filtering to generate a frequency octupling microwave photonic (MWP) signal with 360º phase-shifting based on two cascaded Mach–Zehnder modulators (MZMs). Theoretical analysis is given to realize the high-quality frequency octupling MPPS by eliminating the undesired optical carrier and sidebands using an optical coupler (OC). Simulations show that the generated MMW signal has an electrical spurious suppression ratio (ESSR) higher than 33 dB. The impact of the non-ideal modulation index, extinction ratio, and phase drift is discussed and analyzed. Furthermore, the influence of different center frequencies, power, and linewidths of the laser is also analyzed.

A Microwave Photonic Frequency-Doubling Phase Shifter Based on Dual-Parallel Mach–Zehnder Modulators

A microwave photonic frequency-doubling phase shifter with a broad bandwidth and large tuning range is proposed in this paper. Frequency doubling and phase shifting are realized by processing the input microwave signal in the optical domain at a dual-drive dual-parallel Mach–Zehnder modulator (DD-DPMZM) and a dual-parallel Mach–Zehnder modulator (DPMZM). The input signal is split into two branches through a 90-degree hybrid splitter. One signal is sent to the DD-DPMZM to achieve a phase-shifted carrier-suppressed up-sideband by tuning the bias voltage, and the other is sent to the DPMZM to realize a carrier-suppressed down-sideband. By beating the phase-shifted up-sideband and the down-sideband at a photodetector (PD), the input signal is frequency doubled and phase shifted. The proposed frequency-doubling phase shifter is simulated. The results show that the frequency-doubled signal has a phase-tuning range from 0 to 360 degrees. In addition, the influence of the amplitude and phase unbalance of the 90-degree hybrid splitter on the magnitude variation and phase deviation of the frequency-doubling phase shifter is studied.

Multichannel Microwave Photonic Phase Shifter With Improved Power Efficiency and Suppressed Third-Order Intermodulation Distortions

Multichannel Microwave Photonic Phase Shifter With Improved Power Efficiency and Suppressed Third-Order Intermodulation Distortions

Silicon-Organic Hybrid Electro-Optic Modulator and Microwave Photonics Signal Processing Applications.

Electro-optic modulator (EOM) is one of the key devices of high-speed optical fiber communication systems and ultra-wideband microwave photonic systems. Silicon-organic hybrid (SOH) integration platform combines the advantages of silicon photonics and organic materials, providing a high electro-optic effect and compact structure for photonic integrated devices. In this paper, we present an SOH-integrated EOM with comprehensive investigation of EOM structure design, silicon waveguide fabrication with Slot structure, on-chip poling of organic electro-optic material, and characterization of EO modulation response. The SOH-integrated EOM is measured with 3 dB bandwidth of over 50 GHz and half-wave voltage length product of 0.26 V·cm. Furthermore, we demonstrate a microwave photonics phase shifter by using the fabricated SOH-integrated dual parallel Mach-Zehnder modulator. The phase shift range of 410° is completed from 8 GHz to 26 GHz with a power consumption of less than 38 mW.

On-Chip Photonic Generation of Tunable Wideband Phase-Coded Linearly-Chirped Microwave Waveforms

On-chip photonic generation of tunable wideband phase-coded linearly-chirped microwave waveforms (PC-LCMWs) is proposed and experimentally demonstrated. The on-chip generation system consists of two main parts. One part is a hybrid Fourier-domain mode-locked opto-electronic oscillator (FDML-OEO) for a wideband linearly-chirped microwave waveform (LCMW) generation; the other part is a high-speed microwave photonic phase shifter (MPPS) to perform the phase-coding. By synchronizing the two parts, a PC-LCMW is finally generated. In the proposed chip, a thermally-tunable ultrahigh-Q micro-ring resonator (MRR) is a key component which is incorporated in the FDML-OEO loop to select the oscillation frequency, and an electrically-tunable micro-disk resonator (MDR), as another key component, is used to code the phase of the generated microwave signal while maintaining the amplitude by controlling the free carrier concentration in the lateral PN junction of the disk. With the use of the two key component chips, an experiment is performed and different PC-LCMWs are generated with a tunable center frequency from 12 to 16 GHz, a bandwidth from 2 to 6 GHz, and phase code of 7-bit and 13-bit Barker code. In particular, a PC-LCMW with a maximum bandwidth as wide as 6 GHz and an ultra-large time-bandwidth product (TBWP) as large as 1.96×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> is experimentally demonstrated. The proposed integrated PC-LCMW generation system holds great advantages including ultracompact configuration and fast tunability, which holds a high potential for applications in modern high-resolution multi-functional radar system.

Link Optimization of a Microwave Photonic Phase Shifter Using Brillouin-Induced Low Biasing

Link Optimization of a Microwave Photonic Phase Shifter Using Brillouin-Induced Low Biasing

Reconfigurable second-order optical all-pass filter

Abstract The optical all-pass filter (APF), which exhibits a constant amplitude response and a variable phase response, is a key to manipulating the optical phase without inducing signal amplitude distortion. High-order APFs are significantly demanded because they can afford large time delays and phase shifts. However, to date, only first-order APFs based on lossy waveguides have been reported. Although high-order APFs can be simply obtained by cascading multiple first-order APFs, the complexity and size are increased. To solve this problem, we propose and demonstrate a second-order APF using Mach–Zehnder interferometer-assisted microring resonators. The device is fabricated based on a silicon-on-insulator platform. Based on the second-order APF, an adjustable time delay between 553 and 948 ps is obtained, and the corresponding amplitude variation is less than 1.7 dB. Meanwhile, a microwave photonic phase shifter is also obtained based on the APF. The microwave phase shift can be adjusted from 0 to 3.27π, with an RF power variation within 2.4 dB. Additionally, the second-order APF can be reconfigured to a first-order APF, which significantly enhances its flexibility. The reconfigured first-order APF can realize an adjustable time delay between 257 and 429 ps, and the amplitude variation is less than 0.9 dB. The proposed high-order APF provides a novel approach to manipulating optical signals.

Inline Microring Resonator Based Microwave Photonic Phase Shifter With Self-Mitigation of RF Power Variations

We present a new technique to self-mitigate the RF power variations in microwave photonic phase shifters (MPPS) based on microring resonators by exploiting the root problem of varying optical intensities at different optical phase shifts to harness a varying and opposing optical equalization gain. Whilst optical gain mediums are commonly present in microwave photonic systems to overcome optical loss, choosing an appropriate equalization gain point to strike a balance between the optical gain transformation of weak and preservation of strong signals allows the proposed system to effectively achieve minimal radio frequency (RF) power variation across all signals without interfering with the RF phase shifting operation. Simulation results show an inline MPPS based on the phase and amplitude of conventional resonant structures with a capability to successfully minimize the RF power variations by 80% for up to 25 dB of phase-dependent power variations throughout the full 360° phase tuning range. Experimental results verify the MPPS operation based on a single microring resonator by significantly reducing the large RF power variations from 9 dB to less than ±1.25 dB, while maintaining the same RF phase shifting operation. We then verify the use of the proposed inline MPPS to adaptively minimize the self-interference by optimizing the phase compensation in a self-interference cancellation system. We demonstrate a cancellation bandwidth of 100 MHz with peak in-band cancellation of up to 40 dB while exhibiting the capability to recover weak signals of interest at operating center frequencies ranging from 5 – 20 GHz.

Microwave photonic RF frequency multiplying phase shifter with tunable multiplication factor and a full 360-deg tunable range

Abstract: 提出一种倍频因子连续可调，且相位连续变化的微波光子移相系统。该方案使用两个并联的马赫曾德尔调制器，通过2×2光耦器与两个双并联的集成马赫曾德尔调制器级联，产生可调节的±1～4阶边带，并使用相位调制器对其中一个光波进行相移。通过调整DPMZM的射频驱动信号和直流偏置电压以及PM的直流电压，可以产生相位从0到360度连续可调的2到8次谐波。仿真结果表明，当射频信号频率为10GHz时，可产生频率为20-80GHz的微波信号．调节相位调制器的直流偏置电压与半波电压比值从0到2变化时，对应微波信号的相位从0°到360°变化，可以获得约20dB的大光边带抑制比（OSSR）和电杂散抑制比（ESSR）。此外，分析了调制器消光比对输出微波信号光载波抑制比和电杂散抑制比的影响，以及光载波的波长和功率对微波信号幅度波动的影响。

Silicon Photonic-Based Integrated Microwave Photonic Reconfigurable Mixer, Phase Shifter, and Frequency Doubler

An integrated microwave photonic (IMWP) reconfigurable mixer, phase shifter, and frequency doubler based on the silicon photonics platform is proposed and theoretically investigated in this paper. The proposed structure consists of a novel dual-drive Mach–Zehnder modulator (DDMZM) placed in parallel with an electro-optic phase modulator (PM). The novel DDMZM is a bias-free modulator that has advantages over conventional MZMs, such as bias-free operation and tunable optical-to-carrier sideband ratio (OCSR). The proposed novel structure can be configured as an IMWP phase tunable mixer or IMWP double-balanced mixer by properly adjusting optical wavelength and choosing the proper radio frequency (RF) hybrid coupler. Besides, the proposed IMWP reconfigurable mixer has the ability to perform up-converting, down-converting, RF frequency doubling, and phase shifting. The proposed structure is theoretically analyzed and is verified by simulations.

Independent Amplitude and Phase Control of Two Orthogonal Linearly Polarised Light and Its Applications

A technique to provide independent control on the amplitude and phase of two orthogonal linearly polarised light is presented. It is based on operating a commercial dual-polarisation dual-drive Mach Zehnder modulator (DPol-DDMZM) in reverse direction that routes the input light in slow and fast axis into two different DDMZMs. The technique has the advantage of controlling the phase of the slow-axis light and the amplitude of the fast-axis light has no effect on the light travelling in the orthogonal polarisation state. It has applications in linearised microwave photonic links, frequency multipliers and microwave phase shifters. A new microwave photonic Hilbert transformer based on using the reverse operating DPol-DDMZM to alter the phase of an RF modulation sideband without affecting the orthogonally polarised optical carrier is developed. Experimental results demonstrate 24.3 dB attenuation in the fast-axis light with no change in the slow-axis light, and 0°–360° RF phase shift for only 3.3 V change in DC voltage. The new Hilbert transformer with less than 2.5° phase imbalance and 0.4 dB amplitude ripples over 4–18 GHz frequency range is also demonstrated.

Fast-Reconfigurable Microwave Photonics Phase Shifter Using Silicon Microring Resonators

Thermally controlled silicon photonics microwave phase shifters suffer from slow reconfiguration time that practically limits their application fields. A microwave photonics phase shifter exploiting fast plasma dispersion effect in a silicon microring resonator (MRR) embedding a laterally-doped pn-junction waveguide operating in carrier-depletion mode has been designed and characterized. Proper dimensioning of ring parameters allows moderate insertion loss and limited RF power excursion in correspondence of wide RF phase changes as the space charge region of the junction is modulated by an applied reverse voltage. Experimental results confirm a large modulation bandwidth of more than 5GHz and a phase excursion well in excess of 360° using a cascaded MRRs pair with a residual amplitude modulation down to 2.3 dB.

Microwave Photonic Array Radars

Phased array radars have remarkable advantages over radars with single-element antenna in terms of agility, flexibility, robustness, and reconfigurability. Current pure-electronic phased array radars face challenges when operating with a large frequency tunable range and/or with broad instantaneous bandwidth. Microwave photonics, which allows wide bandwidth, flat frequency response, low transmission loss, and immunity to electromagnetic interference, is a promising solution to cope with issues faced by pure electronics. In this paper, we introduce a general architecture of microwave photonic array radar systems and review the recent advancement of optical beamforming networks. The key elements for modelling the response of the true time delay (TTD) and/or phase-shifting unit are presented and discussed. Two typical array antenna structures are introduced, i.e., microwave photonic phase shifter based array and optical true time delay based array, of which the principle and typical implementations are described. High-resolution inverse synthetic aperture radar (ISAR) imaging is also realized based on a microwave photonic array radar. The possibility of on-chip integration of the microwave photonic array radar is discussed.

A High-Performance Microwave Photonic Phase Shifter Based on Cascaded Silicon Nitride Microrings

A microwave photonic phase shifter based on four cascaded tunable silicon nitride microring resonators is proposed. The phase shifts and RF power variations of the microwave photonic phase shifter were investigated theoretically and experimentally. Good overall performances with full phase tuning range of 400°, low RF power variations of ± 1.5 dB with a broad bandwidth of 11 GHz, fiber to fiber insertion loss about 5.2 dB were achieved. The maximum frequency can be extended to about 40 GHz, which is limited by the MRR’s free spectra range.

Photonic full-range phase shifter with simultaneous tunable frequency multiplying capability based on a DMZM

In this paper, a novel microwave photonic full-range phase shifter with simultaneous frequency-multiplying capability is proposed. The main device is a dual-drive Mach–Zehnder modulator (DMZM) embedded in a Sagnac loop. Under the assistance of two electrical phase shifters (EPS) and a following polarizer (Pol), the optical carrier is eliminated with desired phase tunable carrier-suppressed double-sideband (CS-DSB) signal reserved. So after photoelectric conversion, the frequency-multiplied phase tunable signals are generated. The frequency multiplication factor (FMF) switching and phase tuning operation of multiplied signals can be achieved easily by adjusting the corresponding EPS. The simulation results show that the proposed structure driven by a 10 GHz RF signal can generate a frequency-doubled signal (20 GHz) or frequency-quadrupled signal (40 GHz) that features full-phase tunable range and flat power response. What is more, the proposed phase shifter has a relatively good robustness to the non-ideal factors, large frequency operation range and good frequency tunable capability.

A filterless reconfigurable frequency mixer based on a wideband photonic microwave phase shifter

In this paper, a filterless reconfigurable frequency mixer based on a wideband photonic microwave phase shifter is proposed. The main device is a single PDM-DPMZM which is applied to generate a pair of orthogonally polarized CS-SSB signals. A pair of PCs are followed to introduce a tunable phase to the CS-SSB signals. By changing the detection scheme of the output optical signals and tuning the PCs, single-ended, double-balanced, I/Q, and image-reject mixer can all be achieved with the capability of full range phase shifting. And it can also perform frequency up- and down-conversion switching by adjusting the DC biases of the modulator. A simulation is carried out to demonstrate its versatility, flexibility and reconfigurability. The measured image-rejection ratio of the image rejection mixer is about 65 dB. In addition, the frequency operation range, practical applicability and feasibility are discussed. The effect of non-ideal factors or adjustable parameters, i.e., extinction ratio deterioration, DC biases drift, phase inaccuracy between I/Q path, instability or inaccuracy of the PC and LO signal power variation on system performance are also analyzed.

Microwave Photonic Phase Shifter with frequency up-/down-conversion

In this paper, we propose a microwave photonic phase shifter with frequency conversion (MPSFC) without optically filtering to realize both frequency up- and down-conversion and a full 360º phase-shift for the microwave signal based on an integrated dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM). As the radio frequency (RF) signal is frequency down-converted to intermediate frequency (IF) signal or the IF signal can be frequency up-converted to RF signal, the phase of the output IF or RF signals can be shifted by adjusting the DC bias voltage of PolM. Simulation results demonstrate that both 360º continuously tunable phase shift and frequency conversion can be implemented simultaneously.

Broadband Image-Reject Mixing Based on a Polarization-Modulated Dual-Channel Photonic Microwave Phase Shifter

Broadband image-reject mixing using a dual-channel polarization-modulated photonic microwave phase shifter is proposed and experimentally demonstrated. The polarization-modulated photonic microwave phase shifter is realized by an orthogonal circularly-polarized wavelength generator, an optical coupler, two polarizers, and two photodetectors (PDs). When a local oscillator (LO) signal, a radio-frequency (RF) signal, and an image interference are supplied to the polarization-modulated phase shifter, opposite phase shifts would be introduced to the RF- and image-induced intermediate frequency (IF) signals. By carefully adjusting the polarizers to make the two channels of the phase shifter quadrature, a phase difference of −90 degree is introduced to the RF-induced IF signals in the two channels, while 90-degree phase difference between the image-induced IF signals is produced. With an electrical 90 degree hybrid to combine the two channels, the two RF-induced IF signals will be in phase while those from the image are out of phase. As a result, the image in the downconverted signal is cancelled. An experiment is carried out. An image-reject mixer (IRM) with an image rejection ratio of ∼60 dB for a single-frequency signal and 23 dB for a 4-GHz linear frequency-modulated signal is obtained.

Broadband Brillouin Phase Shifter Utilizing RF Interference: Experimental Demonstration and Theoretical Analysis

Microwave photonic phase shifters based on stimulated Brillouin scattering (SBS) offer tunable and broadband, optically controllable phase shifts. However, achieving a 360° phase shift requires a large amount of SBS gain which often exceeds the available gain and power handling capability of an integrated waveguide. A Radio Frequency (RF) interference technique has recently been utilized in an integrated silicon platform, which uses forward Brillouin scattering in a suspended waveguide to compensate for the lack of available Brillouin gain in standard silicon on insulator platforms. This interference scheme amplifies the phase shift at the expense of link performance. Here, we demonstrate and analytically model a 360° ultra-broadband phase shifter using backward SBS in both fiber and on-chip by combining SBS and RF interference. The phase enhancement scheme greatly reduces the required Brillouin gain and thus the required optical power. Additionally, the backward architecture reduces filter requirements as the residual pump reflections are simpler to remove compared to the pump in the forward Brillouin scattering case, where the pump co-propagates with the signal. The model provides a deeper insight into the properties of the interferometric phase enhancement scheme and predicts the potential trade-offs of an optimized system, showing reduced link loss at higher levels of Brillouin gain. The model also predicts the sensitivity to variations of the interferometric components. Using this technique, we have demonstrated a broadband phase shift over an ultra-broad bandwidth of 0.1 - 65 GHz, limited only by the bandwidth of the available components. Also, we demonstrate a phase enhancement factor of 10 over a bandwidth of 18 GHz in an integrated chalcogenide waveguide.

Wideband and Dispersion Immune Microwave Photonic Phase Shifter With Tunable Optical Carrier to Sideband Ratio

A wideband microwave photonic phase shifter (MPPS) based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) is proposed and experimentally demonstrated. The proposed system has the features of chromatic dispersion (CD) immunity and tunable optical carrier to sideband ratio (OCSR), which can realize long fiber transmission distance with improved power efficiency. It is realized by carrier suppress double sideband (CS-DSB) plus optical carrier (OC) modulation at two orthogonal polarization states. The phases of output RF signals can be tuned continuously and independently by controlling the phases of the OCs. The experiment results show that the continuous 360° phase shifts of output RF signal over 5–25 GHz are both realized in the cases of back-to-back and fiber transmission. No CD-induced power fading and phase severe shaking of the RF signals appear after the dispersion compensating fiber (DCF) of −331 ps/nm at 1545 nm transmission. By optimizing the OCSR of the system, the output RF power efficiency of the proposed scheme realizes significantly improvement when input RF powers and output optical powers are both fixed. The possibility of generating frequency doubling signal is also verified.