Photonic Downconversion Research Articles

Investigation on the performance of photonics-aided W-band millimeter-wave wireless transmission

W-band (75–110 GHz) is a potential radio frequency band to provide long-distance wireless links for mobile data transmission. This paper proposes and experimentally demonstrates high-speed wireless transmission at W-band using photonics-aided method, including optical heterodyne, photonics-aided down-conversion without RF oscillator and coherent detection. A comparison between the photonics-aided method and the conventional electronic method employing solid-state electronic devices is conducted for the first time. The photonics-aided method is shown to offer advantages such as lower harmonic components, spur, reduced nonlinearity, and no local oscillator leakage, results in a 2.5 dB better performance of the photonic-aided W-band mm-wave transmitter compared to the electronic one. In the terms of receiver, the photonics-aided method can surpass the electronic method, with the help of larger electro-optical modulator bandwidth and lower drive voltage in the photonic down-conversion stage. Ultimately, using the photonics-aided method, a recorded equivalent transmission distance of 29 km@84 GHz and 45km@75.6GHz is achieved respectively for 1Gbaud QPSK signal.

Full-duplex coherent analogue mm-wave RoF transmission with simplified RRH and photonic down-conversion of uplink

Full-duplex coherent analogue mm-wave RoF transmission with simplified RRH and photonic down-conversion of uplink

A coherent MMW-ROF link employing mixed modulations and photonic down-conversion

We propose and experimentally demonstrate a coherent millimeter wave radio-over-fiber (MMW-ROF) link employing mixed modulations with a simple digital signal processing (DSP) unit. At the transmitter, a light wave is intensity and phase-modulated by two microwave vector signals in a dual-parallel Mach–Zehnder modulator (DP-MZM). At the receiver, by using a 3-line optical frequency comb (OFC) signal as the optical local oscillator (OLO), the microwave vector signals can be photonically down-converted to intermediate frequency (IF) signals. Then, instead of a complex digital phase-locked loop (DPLL), simple algorithms are used to remove the laser phase fluctuation between two free-running lasers and do the demodulations. In the 25 km fiber transmission experiments, we successfully down-convert two 50 Msymbol/s 16-quadrature amplitude modulation (16-QAM) signals at 25 GHz and 24 GHz to intermediate frequencies of 2 GHz and 1 GHz. The transmission performance of the proposed link in terms of error vector magnitudes (EVMs) are also investigated. The results show that when the receiver optical power is -20 dBm, the measured EVMs are still less than 12.5% which satisfies the 3rd Generation Partnership Project (3GPP) standard.

Ku-band analog photonic down-conversion link with coherent I/Q image rejection and digital linearization.

Analog photonic down-conversion links have been widely used in radar, electronic warfare, and satellite communication systems. Aiming at the optimization demands of the link performance, we demonstrate and experimentally verify a Ku-band photonic down-conversion link based on coherent in-phase/quadrature (I/Q) image rejection and digital nonlinear compensation. The image-rejection ratio at 17.5 GHz is measured to be 47 dB. After digital processing, the image intermodulation distortions (MMD) and the intermodulation distortions (IMD3) are suppressed by 18.1 dB and 10.9 dB, respectively. The corresponding spurious-free dynamic range (SFDR) reaches 108.83 dB·Hz2/3.

Architecture for integrated RF photonic downconversion of electronic signals.

Electronic analog to digital converters (ADCs) are running up against the well-known bit depth versus bandwidth trade off. Towards this end, radio frequency (RF) photonic-enhanced ADCs have been the subject of interest for some time. Optical frequency comb technology has been used as a workhorse underlying many of these architectures. Unfortunately, such designs must generally grapple with size, weight, and power (SWaP) concerns, as well as frequency ambiguity issues which threaten to obscure critical spectral information of detected RF signals. In this work, we address these concerns via an RF photonic downconverter with potential for easy integration and field deployment by leveraging a novel, to the best of our knowledge, hybrid microcomb/electro-optic comb design.

High-frequency characterization of electro-optic modulation chips based on photonic down-conversion sampling and microwave fixture de-embedding.

A self-reference and on-chip method for extracting the intrinsic frequency responses including modulation index and half-wave voltage of electro-optic modulator (EOM) chips is proposed based on photonic down-conversion sampling and microwave fixture de-embedding. The photonic down-conversion sampling is firstly employed to extract the combined response of the source network SxN, the adapter network SAN and the EOM chip. Then the Open-Short-Load (OSL) calibration is exploited to realize the on-chip microwave de-embedding of SxN and SAN in terms of the transmission attenuation and the impedance mismatch. Finally, the power leveling technique is used to track the incident microwave power to obtain the intrinsic half-wave voltage of the EOM chip. Our method features self-reference and on-chip capability, which is applicable for the EOM chips even without a good impedance match, and is free of any extra optical/electrical (O/E) transducer standard, which will be helpful to chip evaluation and packaging optimization.

Non-linear photonic loop mirror based co-site interference canceller

Full duplex-in band (FDIB) is a well-established solution for increasing the data rate and spreading the link range for future communication systems. FDIB systems need no additional bandwidth requirement. However, they are confronted with a major interference challenge on the same site, called co-site interference (CSI). Long-established co-site interference cancellation (CSIC) methods achieve a cancellation depth upto 35 dB, conversely it has space containments, manufacturing imperfections, induces noise penalties and limits isolation bandwidth. To overcome these problems, RF photonic CSIC methods have been developed, which have produced 30 dB wide-band interference suppression. They also increase bandwidth, have a flexible structure, minimize losses and prevent periodic power fading. But these systems have a problem of inherent DC drift, low maintenance of coherence, and low isolation at low transmission power. Thus, there is a high need for photonic CSIC designs of FDIB systems that operate over wider bandwidths and at higher transmission powers. Here, a newfangled CSIC system based on a non-linear photonic loop and frequency down-conversion is proposed. It shows excellent CSIC suppression of greater than 61 dB, for a single frequency signal of interest (SOI) with maximum RF power of 13 dBm. Without frequency down-conversion, the system maintains an average cancellation depth of 62.541 dB for single frequency SOI. After frequency down conversion, the system maintains an average cancellation depth of 61.208 dB for narrow band SOI. The system attains 18% error vector magnitude at −20 dB RF output power, which confirms the comprehensive quality of the system.

Digitally assisted photonic analog domain self-interference cancellation for in-band full-duplex MIMO systems via the LS algorithm with adaptive order.

A digitally assisted photonic analog domain self-interference cancellation (SIC) and frequency downconversion method is proposed for in-band full-duplex multiple-input multiple-output (MIMO) systems using the least square (LS) algorithm with adaptive order. The SIC and frequency downconversion are achieved in the optical domain via a dual-parallel Mach-Zehnder modulator, while the downconverted signal is processed by the LS algorithm with adaptive order that is used to track the response of the multipath self-interference (SI) channel and reconstruct the reference signal for SIC. The proposed method can overcome the reconstruction difficulty of the multipath analog reference signal for SIC with high complexity in the MIMO scenario and can also solve the problem that the order of the reference reconstruction algorithm is not optimized when the wireless environment changes. An experiment is carried out to verify the concept. SIC depths of 30.2, 26.9, 23.5, 19.5, and 15.8 dB are achieved when the SI signal has a carrier frequency of 10 GHz and baud rates of 0.1, 0.25, 0.5, 1, and 2 Gbaud, respectively. The convergence of the LS algorithm with adaptive order is also verified for different MIMO multipath SI signals.

Performance Comparison of Photonic Downconversion for Uplink Mobile Fronthaul

This study compares the performance of photonic downconversion technology using single and dual wavelength modulation methods using an optical phase modulator. We compared the system characteristics, including the conversion gain, phase noise, and spurious-free dynamic range, of the two approaches. To demonstrate the proof-of-concept, we transmitted high-order quadrature amplitude modulation orthogonal frequency-division multiplexing signals in the 43 and 52 GHz bands over the system. The results confirm the potential of the system as a promising solution for uplink mobile fronthaul in high-frequency bands, such as in 5G-Advanced networks.

Broadband dual-channel channelizer based on a microwave photonic power tunable image rejection down-conversion.

Radiofrequency (RF) channelization has potential high frequency and wideband advantages in frequency-domain channel segmentation and down-conversion reception. In this paper, we propose a compact dual-channel channelizer that can process high-frequency wideband signals. It uses double-polarization double-sideband electro-optic modulation and Hartley structure photoelectric conversion to realize down-conversion channelization of the high-frequency wideband signal. The power matching between two polarization signals can be realized by controlling the modulator bias, so the crosstalk between the two output signals can be suppressed. The proposed channelizer has a compact structure since the electro-optic modulation is based on one single laser and one single integrated modulator. No filters are used in the structure, contributing to a very wide RF operation bandwidth and low constraints of laser wavelength. In the experiment, the single frequency signal pairs from 9 GHz to 15 GHz can achieve an inter-channel image rejection ratio of 53 dB. Furthermore, the channelizer slices multi-octave bandwidth quadrature phase shift keying (QPSK) signals up to 16 GHz with the wideband isolation higher than 10 dB and outputs them to two channels in parallel. The error vector magnitudes (EVM) of 9-17 GHz and 18-26 GHz band QPSK signals are guaranteed to be under 23.58% after channelized separation. To the best of our knowledge, the proposed channelizer provides high inter-channel interference suppression at dual-band adjacent signals with 8 GHz bandwidth for the first time. Therefore, the proposed channelizer has great application value for the reception and processing of millimeter signals in the future.

Simple microwave photonic downconversion channelizer based on multi-wavelength laser sources.

This work presents a simple microwave photonic downconversion channelizer based on multi-wavelength laser sources. The design of two laser diode (LD) arrays enables signal multiplexing and simultaneous multichannel downconversion processing, which provide stable, relatively flat, and strong multi-frequency combs. A proof-of-concept experiment was taken, showing that 14.375-17.75 GHz broadband radio frequency (RF) signals were successfully downconverted to the same intermediate frequency (IF) and were sliced into four subchannels with 875 MHz bandwidth showing excellent image rejection and channel uniformity, which agrees with the simulation results. The spurious free dynamic range (SFDR) of the proposed RF channelizer is 100dBHz2/3, the image rejection is over 28 dB, and the frequency measurement error is less than ±6MHz. Replacing optical filters with electrical filters, the proposed simple optoelectronic hybrid reconfigurable microwave photonic channelizer system acquits stable performance and high maturity and meets the application requirements, behaving with stupendous potential in fields such as radar, satellite communication, electronic warfare, and others.

Wideband Microwave Phase Noise Analyzer Based on All-Optical Microwave Signal Processing

An approach for wideband phase noise measurement of microwave signal sources is proposed based on all-optical microwave signal processing. In the proposed scheme, an optical carrier is sequentially modulated by the signal under test (SUT) in a phase modulator and a dual-polarization modulator to generate two +1st-order sidebands with orthogonal polarizations. A time delay is introduced between two sidebands by a span of low-loss optical fiber. Combined with a polarization controller and a polarizer, photonic microwave downconversion with a desired phase shift and time delay can be realized after photodetection, and the phase noise of the SUT can be calculated thereafter. Since all the microwave signal processing functions in the conventional photonic-delay-line-based phase noise measurement system are implemented in the optical domain, the proposed scheme has a large operational bandwidth and a high measurement sensitivity. In the experimental demonstration, accurate phase noise measurement of SUTs is achieved in a frequency range of 10-35 GHz, and a phase noise floor as low as −132.16 dBc/Hz at 10 kHz is obtained.

Transparent Fiber–Millimeter-Wave–Fiber System in 100-GHz Band Using Optical Modulator and Photonic Down-Conversion

We demonstrate the first fiber–millimeter-wave–fiber system in the 100-GHz band using a low-loss optical modulator and direct photonic down-conversion technology. The utilization of a low-loss optical modulator for the direct conversion of a millimeter-wave signal to an optical signal significantly simplifies the millimeter-wave radio receiver because it includes only a radio front-end and an optical modulator. In addition, by adopting direct photonic down-conversion technology for simultaneous detection and down-conversion of the millimeter-wave signal to the microwave band, the fiber–radio receiver and subsequent digital signal processing can be considerably simplified. Using the proposed technologies, we successfully transmitted 32-/64-quadrature amplitude modulation orthogonal frequency division multiplexing and single-carrier signal with a line rate of 71.4 Gb/s and a net data rate of 53.7 Gb/s over a wired and wireless converged system consisting of two optical fiber links and a 20 m radio link at 101 GHz. The proposed system is promising for high-capacity, low-latency, and low-power consumption fiber-wireless transmission in beyond 5G networks.

Digital-Assisted Photonic Analog Wideband Multipath Self-Interference Cancellation

A digital-assisted photonic analog wideband radio-frequency multipath self-interference cancellation (SIC) and frequency downconversion method based on a dual-drive Mach–Zehnder modulator and the recursive least square (RLS) algorithm is proposed and demonstrated for in-band full-duplex systems. Besides the reference for the direct-path self-interference (SI) signal, the RLS algorithm is used to construct another reference for the residual SI signal from the direct path and the SI signals from the reflection paths. The proposed method can solve the performance limitation in the previously reported SIC methods of constructing the multipath SI signal using a single reference which is caused by the limited dynamic range of the digital-to-analog converter when the direct-path SI signal is much stronger than the sub-weak reflection-path SI signals. An experiment is performed. When the carrier frequency of the multipath SI signal is 10 GHz and the direct-path SI signal is much stronger than the sub-weak multipath SI signal, cancellation depths of about 26.7 and 26.1 dB are realized with SI baud rates of 0.5 and 1 Gbaud. When the direct-path SI signal and sub-weak multipath SI signal own closer power, the corresponding cancellation depths are 24.7 and 20.8 dB, respectively.

Wideband Optical Vector Analysis Based on Microwave Photonic Frequency Downconversion

Wideband Optical Vector Analysis Based on Microwave Photonic Frequency Downconversion

Multi-band low-noise microwave-signal-receiving system with a photonic frequency down-conversion and transfer-learning network.

In this Letter, we propose and demonstrate a multi-band signal-receiving system, powered by photonic frequency down-conversion and transfer learning. A photonic frequency down-conversion system directly receives the microwave signals, and the transfer-learning network (TLN) lowers the noise in the signals. In addition to the effectiveness of denoising, the TLN also features ultra-fast retraining for signals of different types or different multi-band frequencies. Experimental results showed that the proposed microwave-signal-receiving system can improve the signal-to-noise (SNR) ratio of signals of different types, SNR, and duty cycles. For network retraining, the TLN requires only three times less data and 10 times less time consumption than conventional training methods.

Microwave photonic frequency down-conversion with self-interference cancellation and SSBI mitigation

In this paper, we proposed a microwave photonic frequency down-conversion scheme with the functions of self-interference cancellation (SIC) and signal–signal beat interference (SSBI) mitigation. The scheme is based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. One of the dual-parallel Mach–Zehnder modulator (DP-MZM) which is located in the upper part of the DP-QPSK modulator is used to achieve SIC by properly biasing the modulator. A local oscillator signal is loaded on the other DP-MZM which is located in the lower part of the DP-QPSK modulator. After photoelectric conversion of the combined optical signal by a photo-detector (PD), the signal of interest (SOI) is down-converted to an intermediate frequency (IF) signal. The SSBI is mitigated by Kramers–Kronig (KK) detection to achieve lower IF down-conversion. Experimental results show that the SIC for a single-tone interference signal is around 53 dB, and for an interference signal with a bandwidth of 100 MHz, the SIC achieved at least 29 dB. A simulation verifies the effect which the least mean square (LMS) algorithm mitigated on the influence of multipath After SIC, we used KK algorithm to reduce error vector magnitude (EVM) of the down-converted 16-QAM signal from 17.54% to 9.07%, which indicates a remarkable SSBI mitigation effect.

Millimeter-wave radio-over-fiber system using optical phase modulation and photonic downconversion for uplink fronthaul transmission.

This Letter proposes a high-performance radio-over-fiber (RoF) system for high-speed and high-fidelity analog waveform transmission of radio signals in the millimeter-wave band in the uplink direction. At the antenna site, the system utilizes a newly fabricated low half-wave voltage broadband phase modulator to convert a millimeter-wave radio signal into an optical signal. At the receiver, by using photonic downconversion and optical filtering technology, a simple direct detection and downconversion of the signal to the microwave band can be achieved simultaneously. As a demonstration of proof of concept, we successfully transmitted a 1024-quadrature amplitude modulation (QAM) narrowband orthogonal frequency-division multiplexing signal at 38 GHz and a 60 Gb/s 64-QAM single-carrier signal at 26.5 GHz over a 20 km RoF system. The system is promising for facilitating the deployment of ultra-dense small cells in high-frequency bands in 5G and beyond networks.

Microwave photonic frequency down-conversion and channel switching for satellite communication.

We present a photonic approach to realize radio frequency (RF) down-conversion and intermediate frequency (IF) channel switching for satellite communication. Conventionally, photonic RF mixers always suffer from limitations of one operational state and one IF channel. We proposed a photonic repeater that can realize multiple frequency down-conversion states and different IF channel switching. Two separated RF ports and two independent local oscillator ports ensure the repeater can down-convert RF signals in different bands simultaneously. Based on the characteristic that orthogonally polarized optical signals cannot beat with each other, the crosstalk between different channels is alleviated. Since no optical filters are involved, the repeater can process broadband RF signals down-conversion and broadband IF signals channel switching. The proposed photonic repeater features compact structure, broad and different bands of operation, and no physical optical splitting, which is promising for a satellite payload.

Linearized analog photonic down-conversion link based on a dual-polarization quadrature phase-shift keying modulator

A novel linearized analog photonic down-conversion link based on an integrated dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is proposed and experimentally verified. Radio frequency and local oscillator signals are fed into the DP-QPSK modulator via an electrical attenuator, respectively. By adjusting the ratio of the two attenuators, the third-order intermodulation distortion can be eliminated based on balanced detection. The scheme is simple and compact and it achieves full spectrum utilization because of using no filter. Experimental results show that the spurious free dynamic range is improved by 16.43 dB for a two-tone signal and the error vector magnitude is improved by 6.16% for a 100-MSym/s 16-quadrature-amplitude-modulation signal.