Ultra-low noise dual-frequency VECSEL at telecom wavelength using fully correlated pumping

Abstract

An ultra-low intensity and beatnote phase noise dual-frequency vertical-external-cavity surface-emitting laser is built at telecom wavelength. The pump laser is realized by polarization combining two single-mode fibered laser diodes in a single-mode fiber, leading to a 100% in-phase correlation of the pump noises for the two modes. The relative intensity noise is lower than -140 dB/Hz, and the beatnote phase noise is suppressed by 30 dB, getting close to the spontaneous emission limit. The role of the imperfect cancellation of the thermal effect resulting from unbalanced pumping of the two modes in the residual phase noise is evidenced.

Fully–correlated multi–mode pumping for low–noise dual–frequency VECSELs

“…It is worth noticing that, in the model for the thermal noise, the fact that the correlation amplitude η of the pump noises is not strictly equal to 1 leads to a larger contribution to the beat note phase noise than the unbalanced pumping of the two modes P p,x P p,y . We could thus expect a stronger phase noise suppression to occur with a single-mode fibered pump ensuring η = 1 and delivering enough power like in [9], provided such a single-mode fiber-coupled highpower diode laser would exist around 673 nm. Furthermore, we observe a discrepancy reaching almost 10 dB at 10 kHz between the model and the measurements.…”

“…However, this solution cannot be applied to several wavelengths for which either there simply exists no commercial single-mode fibered pump laser, or there is a power issue. Pumping 1.5 µm dual-frequency VECSELs using currently available single-mode fibered pump diodes requires a trick, as reported in [9], otherwise the power delivered to the structure is not sufficient. In the particular case of 852 nm VECSELs for example, no commercial single-mode fibered laser diode is currently available with enough power.…”

Direct measurement of the spectral dependence of Lamb coupling constant in a dual frequency quantum well-based VECSEL

“…In semiconductor active media, dual-polarization oscillation has been already demonstrated in semiconductor Quantum Well (QW) based Vertical External Cavity Surface Emitting Lasers (VECSELs), at 1 μm [15][16][17], at 852 nm [18,19], as well as at telecom wavelengths [20,21]. The use of such semiconductor structures in an external cavity enables class-A operation of the laser without relaxation oscillations leading naturally to low intensity noise oscillation.…”

Thermal phase fluctuations in optically pumped dual-frequency vertical external-cavity surface-emitting lasers for cesium clocks based on coherent population trapping

“…However, since the same laser pumps the two modes, one needs to take into account the correlations between the pump power fluctuations seen by these two modes. 17 The modulus η and the phase ψ of this correlation have been shown to be to a large extent independent of the noise frequency in the range of frequencies that we consider here (1 kHz to 20 MHz). In these conditions, the PSD S f T f ð Þ of the beatnote phase noise induced by the pump fluctuations is related to the optical phase noise PSD S _ ψ f ð Þ through the following relation: 17…”

“…Noise investigations in VECSELs have led to a quantitative understanding and description of at least the two first sources of noise. 4,9,[11][12][13][14][15][16][17][18] The description of the two other sources of noise deserves more effort, especially the thermal noise. These fluctuations of the local temperature induce changes of the effective optical length of the laser cavity and thus of the laser phase.…”