126 research outputs found
Intensity and phase noise correlations in a dual-frequency VECSEL operating at telecom wavelength
The amplitude and phase noises of a dual-frequency vertical-external-cavity
surface-emitting laser (DF-VECSEL) operating at telecom wavelength are
theoretically and experimentally investigated in detail. In particular, the
spectral behavior of the correlation between the intensity noises of the two
modes of the DF-VECSEL is measured. Moreover, the correlation between the phase
noise of the radio-frequency (RF) beatnote generated by optical mixing of the
two laser modes with the intensity noises of the two modes is investigated. All
these spectral behaviors of noise correlations are analyzed for two different
values of the nonlinear coupling between the laser modes. We find that to
describe the spectral behavior of noise correlations between the laser modes,
it is of utmost importance to have a precise knowledge about the spectral
behavior of the pump noise, which is the dominant source of noise in the
frequency range of our interest (10 kHz to 35 MHz). Moreover, it is found that
the noise correlation also depends on how the spatially separated laser modes
of the DF-VECSEL intercept the noise from a multi-mode fiber-coupled laser
diode used for pumping both the laser modes. To this aim, a specific experiment
is reported, which aims at measuring the correlations between different spatial
regions of the pump beam. The experimental results are in excellent agreement
with a theoretical model based on modified rate equations
Noise investigation of a dual-frequency VECSEL for application to Cesium clocks
We theoretically and experimentally study the noise of a class-A
dual-frequency vertical external cavity surface emitting laser operating at
Cesium clock wavelength. The intensity noises of the two orthogonally polarized
modes and the phase noise of their beatnote are investigated. The intensity
noises of the two modes and their correlations are well predicted by a theory
based on coupled rate equations. The phase noise of the beatnote is well
described by considering both thermal effects and the effect of phase-amplitude
coupling. The good agreement between theory and experiment indicates possible
ways to further decrease the laser noises
Fully-correlated pumping for dual-frequency VECSELs dedicated to cesium CPT clocks
We report a fully-correlated multi-mode pumping architecture optimized for
dramatic noise reduction of a class-A dual-frequency Vertical External Cavity
Surface Emitting Laser (VECSEL). Thanks to amplitude division of a laser diode,
the two orthogonally polarized modes emitted by the VECSEL oscillating at 852
nm are separately pumped by two beams exhibiting fully in--phase correlated
intensity noises. This is shown to lead to very strong and in-phase
correlations between the two lasing modes intensities. As a result, the phase
noise power spectral density of the RF beat note generated by the two modes
undergoes a drastic reduction of about 10 to 20 dB throughout the whole
frequency range from 10 kHz to 20 MHz and falls below the detection floor above
a few MHz. A good agreement is found with a model which uses the framework of
rate equations coupled by cross--saturation. The remaining phase noise is
attributed to thermal effects and additional technical noises and lies mainly
within the bandwidth of a phase-locked-loop
Phase Noise of the Radio Frequency (RF) Beatnote Generated by a Dual-Frequency VECSEL
We analyze, both theoretically and experimentally, the phase noise of the
radio frequency (RF) beatnote generated by optical mixing of two orthogonally
polarized modes in an optically pumped dual-frequency Vertical External Cavity
Surface Emitting Laser (VECSEL). The characteristics of the RF phase noise
within the frequency range of 10 kHz - 50 MHz are investigated for three
different nonlinear coupling strengths between the two lasing modes. In the
theoretical model, we consider two different physical mechanisms responsible
for the RF phase noise. In the low frequency domain (typically below 500 kHz),
the dominant contribution to the RF phase noise is shown to come from the
thermal fluctuations of the semicondutor active medium induced by pump
intensity fluctuations. However, in the higher frequency domain (typically
above 500 kHz), the main source of RF phase noise is shown to be the pump
intensity fluctuations which are transfered to the intensity noises of the two
lasing modes and then to the phase noise via the large Henry factor of the
semiconductor gain medium. For this latter mechanism, the nonlinear coupling
strength between the two lasing modes is shown to play an important role in the
value of the RF phase noise. All experimental results are shown to be in good
agreement with theory
Ramsey CPT Signal Generation with a Miniature Clock Bench and a Dual-Frequency Optical Generator
We demonstrate, for the first time, Ramsey CPT spectroscopy with a miniature
electro-optical bench associated to a dual-frequency generator based on
combined optical injection locking and optical phase locking techniques
Preliminary results show Ramsey CPT resonance with a contrast of 2% at the
Cesium D2 line. Frequency difference locking loops lead to a contribution of
Dick effect to fractional frequency stability lower than 1.7x10-13 at 1 s, in
line with targeted clock stability of 5x10-13 at 1 s
Ultra-low noise dual-frequency VECSEL at telecom wavelength using fully correlated pumping
International audienceAn 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
Dual frequency emission in a compact semiconductor laser for coherent population trapping cesium atomic clocks
We present the dual-frequency emission of a diode-pumped vertical external-cavity semiconductor laser at 852 nm dedicated to coherent population trapping experiments. With a compact cavity more than 10mW is demonstrated in each polarization, with a frequency difference in the GHz range. One polarization has been stabilized on an atomic transitio
Coherent dual-frequency emission of a vertical external-cavity semiconductor laser at the cesium D2 line
International audienceWe describe the dual-frequency and dual-polarization emission of a diode-pumped vertical external-cavity semiconductor laser at 852 nm dedicated to the coherent population trapping of cesium atoms. The output power reaches ∼20 mW on each frequency, with a frequency difference in the GHz range
Tunable high-purity microwave signal generation from a dual-frequency VECSEL at 852 nm (orale)
International audienceWe demonstrate the dual-frequency emission of a diode-pumped vertical external-cavity semiconductor laser operating at 852 nm, dedicated to the coherent population trapping of cesium atoms for compact atomic frequency references. It is based on a single laser cavity sustaining the oscillation of two adjacent, cross-polarized, modes. The output power reaches 10 mW on each frequency. The frequency difference and the absolute laser frequencies are simultaneously precisely tuned and stabilized on external references, resulting in the generation of a high-purity optically-carried microwave signal. The laser design has focused on stability and compactness
Emission bifréquence d'un laser à semiconducteur en cavité externe à 852 nm pour les horloges atomiques a césium (orale)
National audienceNous décrivons l'émission simultanée en phase, sur deux fréquences optiques polarisées perpendiculairement, d'un laser à semiconducteur en cavité externe pompé optiquement. L'émission est accordable autour de la raie D2 du césium à 852,14 nm avec une puissance optique d'environ 13 mW sur chaque polarisation. La différence de fréquence est ajustée grâce à un modulateur électro-optique autour de 9,2 GHz. Nous évaluons la source réalisée en vue de son application au piégeage cohérent de population d'atomes de césium dans une horloge atomique
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