Photonic generation of stable microwave signals from a dual-wavelength Al_2O_3:Yb^3+ distributed-feedback waveguide laser

Abstract

We report the fabrication and characterization of a dual-wavelength distributed-feedback channel waveguide laser in ytterbium-doped aluminum oxide. Operation of the device is based on the optical resonances that are induced by two local phase shifts in the distributed-feedback structure. A stable microwave signal at ~15 GHz with a -3 dB width of 9 kHz was subsequently created via the heterodyne photodetection of the two laser wavelengths. The long-term frequency stability of the microwave signal produced by the free-running laser is better than ±2.5 MHz, while the power of the microwave signal is stable within ±0.35 dB.

Carrier generation using a dual-frequency distributed feedback waveguide laser for phased array antenna (PAA)

“…The weak longitudinal mode interaction was confirmed by the longitudinal field overlap between the two modes ( Fig. 2), which was calculated to be 0.34 [14]. Moreover, for a period of 45 min the power of the microwave signal was stable within ± 0.35 dB [14].…”

“…A 10 mm long surface corrugated Bragg grating was defined by means of laser interference lithography and etched into the top surface of the SiO 2 layer with reactive ion etching. The detail process of fabricating the waveguide is explained in [14]. In order to realize the two required quarter-wavelength phase shifts, two sections with 2 mm long adiabatic sinusoidal widening of the waveguide width are fabricated [20].…”

“…Each of the bragg reflectors was designed to have a grating coupling coefficient of k = 6 cm −1 . Fabrication of the waveguide and Bragg gratings is described in detail in [14].…”

“…Moreover, such scheme is rather bulky and suffers from large frequency drift of the microwave carriers. Heterodyning of two optical frequencies coming from a single laser cavity has shown its potential on improvement of frequency stability [14]. In this regard a dual-frequency laser (DFL) is interesting as the relative fluctuations between the two frequencies are low and can be used to generate a low-phase-noise microwave carrier due to the common-mode noise rejection effect [13,[15][16][17].…”

“…In this paper we consider an optically generated carrier based on heterodyning of a dual-frequency laser reported recently [14]. This laser is in ytterbium-doped aluminum oxide (Al 2 O 3 : Yb 3+ ) fabricated on a silicon substrate, which shows great potential for the monolithic integration of optically generated microwave sources.…”