Observation of phase noise reduction in photonically synthesized sub-THz signals using a passively mode-locked laser diode and highly selective optical filtering

Comparison of Monolithic Optical Frequency Comb Generators Based on Passively Mode-Locked Lasers for Continuous Wave mm-Wave and Sub-THz Generation

“…When two sources are used, continuous tunability is provided, but to obtain good phase noise characteristics of the generated signal complex optical phase-locked loops (OPLL) are needed to correlate the noise from both sources and attain a stable THz signal. In the case of using one source, this can be a dual-mode structure [21], where very limited tunability is offered, or a multimode optical source 0733-8724/$31.00 © 2012 IEEE (optical frequency combs), where discrete tunability (multiples of the fundamental repetition frequency) is provided using high selective optical filtering [22] or optical injection locking (OIL) [23] to select two modes from the optical spectrum. As the optical modes used for the THz signal generation are phase-locked and a narrow optical linewidth can be used, extremely low noise and narrow THz signals can be generated.…”

“…Nevertheless there are other devices, with much higher integration potential, that can be used as OFCG as are mode-locked laser diodes (MLLD) [22] or more recently, high-Q silicon-nitride spiral resonators [25]. While the latter resonators don't offer good phase noise characteristics and are not mature enough for integration, MLLDs are devices that can be integrated as PICs and are able to offer extremely low phase noise at less than 1 MHz offset from the carrier both under passive [26] regime and specially under active or hybrid regime [26].…”

“…Generation of sub-THz signals using both devices at GHz and GHz is accomplished with the help of a photonic synthesis scheme based on the optical filtering of two modes from a multimode source and its photomixing in a high bandwidth photodiode [22]. The synthesized signals are evaluated in terms of electrical linewidth and compared to the reference information of the two different PMLLD topologies.…”

“…As stated in the Introduction, a PMLLD is suitable to be used as OFCG in any optical heterodyning setup based on the photomixing of two longitudinal modes from a multimode source, like those described on [18], [22], [23]. For the analysis presented here, the scheme reported in [22] based on optical filtering is used.…”

Sub-picosecond pulse and terahertz optical frequency comb generation by monolithically integrated linear mode-locked laser

“…Integrated passively mode-locked semiconductor lasers are robust and compact sources for generating coherent optical frequency combs which are of great interests in communications, metrology, spectroscopy and millimeter wave/terahertz (mmW/THz) generation [1][2][3]. Unlike other optical frequency comb generation techniques, it does not require any external RF source or optical pump.…”