Microwave frequency multiplication based on external modulation using two cascaded Mach-Zehnder modulators (MZMs) has been considered an effective solution for high-frequency and frequency-tunable microwave signal generation. Different techniques have been demonstrated recently, but no generalized approach has been developed. In this paper, a generalized approach to achieving microwave frequency multiplication using two cascaded MZMs is presented. A theoretical analysis leading to the operating conditions to achieve frequency quadrupling, sextupling, or octupling is developed. The system performance in terms of phase noise, tunability, and stability is also investigated.

Investigation of Photonically Assisted Microwave Frequency Multiplication Based on External Modulation

5G communications require a multi Gb/s data transmission in its small cells. For this purpose millimeter wave (mm-wave) RF signals are the best solutions to be utilized for high speed data transmission. Generation of these high frequency RF signals is challenging in electrical domain therefore photonic generation of these signals is more studied. In this work, a photonic based simple and robust method for generating millimeter waves applicable in 5G access fronthaul is presented. Besides generating of the mm-wave signal in the 60 GHz frequency band the radio over fiber (RoF) system for transmission of orthogonal frequency division multiplexing (OFDM) with 5 GHz bandwidth is presented. For the purpose of wireless transmission for 5G application the required antenna is designed and developed. The total system performance in one small cell was studied and the error vector magnitude (EVM) of the system was evaluated.

Towards 5G: A Photonic Based Millimeter Wave Signal Generation for Applying in 5G Access Fronthaul.

The broad bandwidth and low loss offered by modern photonics have led to an ever-increasing interest in the design and implementation of photonically assisted systems for the genera- tion, processing, control and distribution of microwave signals, an area called microwave photonics. In this article, a tutorial on microwave photonics is presented with an emphasis on photonic true-time delay beamforming, radio-over-fiber and UWB-over- fiber distribution and photonic analog-to-digital conversion.

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A Tutorial on Microwave Photonics

What we believe to be a new scheme to generate an optical millimeter wave with octupling of the local oscillator via a nested LiNbO3 Mach-Zehnder modulator (MZM) is proposed and implemented by numerical simulation. Since the response frequency of the modulator and the local frequency are largely reduced, the bandwidth requirement of the transmitter to the optical and electrical components is reduced greatly. Then, the parameters of the nested modulator are analyzed theoretically, and we find that both the extinction ratio of the MZM and the phase imbalance between its two arms have influence on the performance of the generated optical millimeter wave.

Optical millimeter wave generated by octupling the frequency of the local oscillator

To reduce the nonlinear distortion in electrical devices, optical modulators, and transmission fiber, we adopt a companding transform coding technique to reduce the peak-to-average power ratio of the orthogonal frequency division multiplexing (OFDM) signal in an OFDM radio-over-fiber system. By adopting this technique, our experimental results show that the receiver sensitivity at a bit error ratio of 1 × 10-3 for a 2.98 Gb/s OFDM signal carried on a 60 GHz optical millimeter-wave after 50 km of standard single-mode fiber transmission is improved by about 0.6, 2.2, and 3.8 dB at launch powers of 0, 6, and 12 dBm, respectively.

Reducing the peak-to-average power ratio with companding transform coding in 60 GHz OFDM-ROF systems

A novel scheme to implement duplex 60-GHz radio-over-fiber link with 20-GHz double-sideband optical millimeter-wave transmitted along the fiber

Generation and transmission of the double-sideband optical millimeter-wave with signal carried only by optical carrier

The transmission performance of the single sideband optical millimeter-wave with BPSK signal in the duplex radio-over-fiber link

Underwater optical wireless communication, which is useful for oceanography, environmental monitoring, and underwater surveillance, suffers the limit of the absorption attenuation and Mie–Rayleigh scattering of the lights. Here, Bessel-like beams generated by a fiber microaxicon is utilized for underwater wireless propagation. Underwater, the cone angle for generating Bessel-like beams starts from 46°, which is smaller than that in air for Bessel-like beams. When the cone angle of the fiber microaxicons is about 140°, the depth of focus underwater, which is four times as long as the depth of focus in air, has enlarged about 28 μm, 36.12 μm, and 50.7 μm for 470 nm, 520 nm, and 632 nm visible lights. The transmission distance of the Bessel beams for visible lights has been simulated by using Henyey–Greenstein–Rayleigh phase function methods and spectral absorption by bio-optical model due to Monte Carlo methods. The results show that the propagation distance could reach 4000 m, which overcome the limit of the Mie–Rayleigh scattering and absorption attenuation underwater.

Lan Rao

Papers

Optical millimeter wave generated by octupling the frequency of the local oscillator

A novel scheme to implement duplex 60-GHz radio-over-fiber link with 20-GHz double-sideband optical millimeter-wave transmitted along the fiber

Generation and transmission of the double-sideband optical millimeter-wave with signal carried only by optical carrier

The transmission performance of the single sideband optical millimeter-wave with BPSK signal in the duplex radio-over-fiber link

Underwater Bessel-like beams with enlarged depth of focus based on fiber microaxicon