Intensity noise correlations in a two-frequency VECSEL

S De,F Bretenaker,A El Amili,V Pal,M Alouini,R Ghosh,I Sagnes,G Baili,G Pillet

doi:10.1364/oe.21.002538

Abstract

We present an experimental and theoretical study of the intensity noise correlation between the two orthogonally polarized modes in a dual frequency Vertical External Cavity Surface Emitting Laser (VECSEL). The dependence of the noise correlation spectra on the non-linear coupling between the two orthogonally polarized modes is put into evidence. Our results show that for small coupling the noise correlation amplitude and phase spectra remain nearly flat (around -6 dB and 0° respectively) within the frequency range of our interest (from 100 kHz to 100 MHz). But for higher values of the coupling constant the low frequency behaviors (below 1-2 MHz) of the correlation amplitude and phase spectra are drastically changed, whereas above this cut-off frequency (1-2 MHz) the correlation spectra are almost independent of coupling strength. The theoretical model is based on the assumptions that the only source of noise in the frequency range of our interest for the two modes are pump noises, which are white noises of equal amplitude but partially correlated.

Highlights

Optical generation, transport, or processing of radio-frequency (RF) signals becomes more and more important for many applications
If we compare the results of different coupling situations (1 mm, 0.5 mm and 0.2 mm thick birefringent YVO4 crystal (BC) respectively), we find that the low frequency behaviors of the noise correlation spectra as well as the relative intensity noise (RIN) spectra are depending on the strength of coupling, whereas above this cut-off frequency the behaviors remain almost unchanged for different coupling situations
5HFHLYHG2FWUHYLVHG-DQDFFHSWHG-DQSXEOLVKHG-DQ 11 February 2013 / Vol 21, No 3 / OPTICS EXPRESS 2549 the correlation is very low up to 1-2 MHz, but above this cut-off frequency the amplitude of correlation is high. We have shown both experimentally and theoretically that the intensity fluctuations for the two orthogonally polarized modes in a dual frequency Vertical External Cavity Surface Emitting Laser (VECSEL) are partially correlated the two modes are pumped by the same pump source and oscillating inside the same cavity

Summary

Introduction

Transport, or processing of radio-frequency (RF) signals becomes more and more important for many applications. Rather than modulating a single-frequency laser or beating two separate lasers, the direct generation of an optically carried RF beat note in a two-frequency laser is a promising strategy for the optical distribution and generation of radar local oscillators [3], and for pulsed or CW lidarradar systems [4] Such dual frequency operation has been demonstrated for diode pumped solid-state lasers, e.g., Nd:YAG [5], Er:Yb:Glass [6] and Yb3+:KGW lasers [7]. The main limitation of these solid-state two-frequency lasers lies in their relatively strong intensity noise inherent to their class-B dynamical behavior [8,9] This is the reason why dual-frequency operation has recently been demonstrated in a class-A VECSEL, since such two-frequency VECSELs do not suffer from relaxation oscillations. As a result the frequency difference between the two modes can be tuned by changing the intra-

Methods

Discussion

Conclusion