Non-linear optoelectronic phase-locked loop for stabilization of opto-millimeter waves: towards a narrow linewidth tunable THz source

Abstract

We propose an optoelectronic phase-locked loop concept which enables to stabilize optical beat notes at high frequencies in the mm-wave domain. It relies on the use of a nonlinear-response Mach-Zehnder modulator. This concept is demonstrated at 100 GHz using a two-axis dual-frequency laser turned into a voltage controlled oscillator by means of an intracavity electrooptic crystal. A relative frequency stability better than 10⁻¹¹ is reported. This approach of optoelectronic down conversion opens the way to the realization of continuously tunable ultra-narrow linewidth THz radiation.

Bridging the gap between THz and microwave photonics through optoelectronic generation of interleaved combs Invited paper

“…The proposed two-propagation-axis laser of Fig. 2 is extensively described in [23]. It offers a large tunability of the frequency difference up to 2 THz.…”

“…In order to overcome this limit, the optoelectronic modulation has to be highly nonlinear so that it generates combs around each optical carrier. To this aim, the MZM used for optoelectronic down-conversion is now replaced by a custom MZM specifically optimized by Photline technologies in order to provide a strong nonlinear response [23]. Consequently, when the dual-axis DFL beam is sent into this MZM, several harmonics of the driving frequency, f RF , are generated around each optical frequency.…”

“…The OEPLL experiment is similar to the previous one except that the standard MZM is now replaced by the nonlinear MZM of section 4 and the correction signal is sent to the intracavity electro-optic crystal located in one arm of the laser. Obviously, the electronic filtering and amplification stages have been redesigned in order to fit the new characteristics of the voltage controlled oscillator formed by the two-axis laser [23]. As illustration, we have tested this approach in the same conditions as in Fig.…”

Synchronization of Two DFB Lasers Using Frequency-Shifted Feedback for Microwave Photonics

“…Finally, their microwave output can be locked on electronic local oscillators at lower frequency (e.g. 10 GHz) using various downconversion techniques [22,23].…”

Vertical-external-cavity surface-emitting laser for THz generation

“…Another technique used to reduce mode coupling consists in a separation of laser beams within the cavity. Such a two-axis cavity can be obtained for example by polarization separation [9] and shows interesting results in terms of tunability and coherence. However, tunability occurs by steps, output power is limited to few milliwatts, cavity is complex with intra-cavity movable elements, almost impossible to integrate on a single device, and coherence is degraded.…”