Optical Frequency Tuning for Coherent THz Wireless Signals

Abstract

THz wireless signals have become of interest for future broadband wireless communication. In a scenario where the wireless signals are distributed to many small remote antenna units, this will require systems which allow flexible frequency tuning of the generated THz carrier. In this paper, we demonstrate experimentally the implementation of two tuning methods using an optical frequency comb generator for coherent optical frequency tuning in THz wireless-over-fiber systems. The first method is based on using a photonic integrated circuit optical phase lock loop (OPLL) subsystem implemented as a high quality optical filter for single comb line selection and optical amplification. The OPLL generates an optical carrier, which is frequency and phase stabilized in reference to one of the optical comb lines with a frequency offset precisely selectable between 4 and 12 GHz. The second method is based on optical single sideband suppressed carrier (SSB-SC) modulation from the filtered comb line using an optical IQ modulator. With this technique, it is possible to suppress the other unwanted optical tones by more than 40 dB. This generated optical carrier is then heterodyned with another filtered optical comb line to generate a tuneable and stable THz carrier. The full system implementations for both methods are demonstrated by transmitting THz wireless signal over fiber with 20 Gb/s data in QPSK modulation. The system performance and the quality of the generated THz carrier are evaluated for both methods at different tuned THz carrier frequencies. The demonstrated methods confirm that a high quality tuneable THz carrier can easily be implemented in systems where dynamic frequency allocation is required.

Ultra-high-resolution software-defined photonic terahertz spectroscopy

“…There is very large flexibility in the choice of modulator. For example, replacing the intensity modulator with an in-phase quadrature-phase (IQ) modulator would allow a software-defined scan of transmission spectra using single-sideband suppressedcarrier modulation [72], without adjusting any other element (e.g., frequency comb) of the instrument. However, this would be limited by the maximum achievable modulator bandwidth.…”

Photonic systems for tunable mm-wave and THz wireless communications

“…The first one [2], [3], tackles the problem a priori (i.e., at the transmitter) and relays on the generation of an optical frequency comb. A comb is formed by multiple optical wavelengths all equidistant from each other (comb spacing) and all phase locked to each other.…”

Generation of frequency 16‐tupling millimeter wave without filtering based on cascaded Mach–Zehnder modulator

“…The MMW signal generated by photons has the advantages of broad bandwidth and high spectrum purity, so it is an ideal scheme to use photons to generate high-frequency MMW signals. 2 Many researchers have proposed many methods to generate high-frequency millimeters wave signals, such as optical injection locking, 3,4 optical phase-locked loop, 5 dual-wavelength laser, 6,7 nonlinear effects (such as fourwave mixing), 8,9 optoelectronic oscillator, [10][11][12] and external modulation. [13][14][15][16][17] Because the external modulation scheme has the advantages of high spectrum purity, wide tuning range, good stability, and low phase noise, it shows great potential in high-frequency signal generation.…”