The millimeter-wave (mm-wave) frequency band has emerged as a means to overcome current radio frequency spectral limitations and represents an interesting solution to fulfill the bandwidth and networking requirements of fifth generation (5G) mobile communications and beyond. Photonic generation of these frequencies holds advantages over electronic methods in terms of cost and effective network distribution. Due to their coherent nature, optical frequency combs (OFC) are a promising solution for the efficient generation of mm-wave frequencies. The work outlined examines the use of OFCs in a mm-wave radio-over-fiber (RoF) heterodyne system with regard to the specific requirements of a 5G candidate waveform, universally filtered orthogonal frequency division multiplexing. Through experimentation and simulation, the key limitations of linewidth, effective path length difference, and relative intensity noise (RIN) are explored. Results are presented, in terms of error vector magnitude (EVM), for a wide range of system parameters highlighting important considerations to be taken in designing future mm-wave RoF systems employing OFCs. Performance of ∼5% EVM using single sideband modulation is achieved for optimized system conditions and an RIN level of −132 dB/Hz.

Modulation cancellation and signal inversion are demonstrated within reflective semiconductor optical amplifiers. The effect is necessary to implement colorless optical network units for network end-users, where downstream signals need to be erased in order to reuse the carrier for upstream transmission. The results presented here indicate that reflective semiconductor optical amplifiers possess the perfect high-speed all-optical gain saturation characteristics to completely cancel the downstream modulation at microwatt optical power levels and are thus the prime candidate to be constituents of future optical network units. Theoretical considerations are supported by experiments that show the cancellation of signals with a 6 dB extinction ratio at 2.5 Gbit/s.

We report an experimental characterization of additive noise from a single-stage phase shifter based on slow and fast light propagation in a bulk semiconductor optical amplifier. We examine the influence of redshifted sideband suppression and optical input power on the signal-to-noise ratio (SNR) of the detected signal. We conclude that in spite of the up to a 6 dB reduction in the detected noise, the SNR remains dominated by the decrease in the detected signal power.

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