QAM-GFDM of Dual-Mode VCSEL Mixed 28-GHz MMW Carrier for Fiber-Wireless Link

An optical heterodyned 28-GHz carrier generation is demonstrated for synthesizer-free fifth-generation (5G) millimeter wave over fiber (MMWoF) link by using orthogonally polarized dual-mode vertical-cavity surface-emitting laser (VCSEL) as the frontend transmitter, and the power envelope detection is employed for self-heterodyne down-conversion of the generalized frequency division multiplexing (GFDM) data stream. The demonstrated MMWoF link exhibits superior immunity to the residual frequency and phase noises as well as the inter-carrier interference induced by the free-running dual-mode carrier. For back-to-back optical downstream wireline transmission, the receiving GFDM data optimizes its bit error rate (BER) to 2.2×10
⁻⁴
by adjusting the bias current of the dual-mode VCSEL to 8 mA (3 I
_th
), and by grouping the GFDM data matrix with total symbols of
N = K×M
with
K
= 2 subcarriers and
M
= 24 timeslots. After a long-reach delivering the optical data stream over 50-km dispersion-managed single-mode fiber (DM-SMF), the qualified receiving power sensitivity is −12 dBm, whereas the decoding GFDM data reveals improved receiving sensitivity with an extremely low power penalty of only 0.3 dB. For the wireless transmission after optical downstream receiving at the remote node, the self-heterodyned MMW carrier exhibits peak power of −62.3 dBm and carrier-to-noise (CNR) of 26.8 dB over long-reach 50-km DM-SMF downstream optical link. In comparison with the mutual heterodyned from two incoherent optical carriers, the self-heterodyned frequency fluctuation can be suppressed from >500 to <330 MHz with significantly suppressed phase noise. After wireless delivering over 2 m in free space, the self-heterodyne down-conversion by power envelope detection guarantees the down-converted quadrature amplitude modulation GFDM (QAM-GFDM) data stream with an average power of -48.4 dBm after optimizing the impedance matching by selecting the appropriate frequency response of the power envelope detector. As a result, the wireless MMW transmission of 8-Gbit/s 4-QAM GFDM data stream is qualified with error vector magnitude (EVM) of 16.9%, signal-to-noise ratio (SNR) of 8.5 dB, and BER of 3.8×10
⁻³
. By combining the free-running dual-mode source with two advanced techniques including mode-power equalization and self-heterodyned power envelope detection, the proposed synthesizer-free MMWoF network has demonstrated excellent immunity to the phase/frequency noise, inter-carrier interference which is particularly suitable for building up the compact and simplified optical transmitter and microwave receiver modules with cost-effective MMW self-heterodyne scheme.