Laser phase noise (PM) to transmitted intensity noise (AM) conversion is a fundamental aspect of the field/matter interaction, and a major noise process that limits the frequency stability of next-generation atomic clocks. It arises from the absorption cross section’s dependence on laser phase and is especially pernicious for vertical-cavity surface-emitting lasers (VCSELs) given their relatively broad singlemode linewidths (e.g., 40 MHz). This is unfortunate, since VCSELs (with their very low operating power and low probability for mode hops) are otherwise ideal for quantum devices. Here, we demonstrate that atomic spectroscopy with N VCSELs reduces the total PM-to-AM noise by a factor of ~N1/2. Consequently, atomic clocks with (for example) five VCSELs would have a signal-to-noise ratio (SNR5) approximately 120% higher than the same device operating with one VCSEL (SNR1) at the same total power: SNR5/SNR1≌ 2.2.Laser phase noise (PM) to transmitted intensity noise (AM) conversion is a fundamental aspect of the field/matter interaction, and a major noise process that limits the frequency stability of next-generation atomic clocks. It arises from the absorption cross section’s dependence on laser phase and is especially pernicious for vertical-cavity surface-emitting lasers (VCSELs) given their relatively broad singlemode linewidths (e.g., 40 MHz). This is unfortunate, since VCSELs (with their very low operating power and low probability for mode hops) are otherwise ideal for quantum devices. Here, we demonstrate that atomic spectroscopy with N VCSELs reduces the total PM-to-AM noise by a factor of ~N1/2. Consequently, atomic clocks with (for example) five VCSELs would have a signal-to-noise ratio (SNR5) approximately 120% higher than the same device operating with one VCSEL (SNR1) at the same total power: SNR5/SNR1≌ 2.2.

IEEE Open Journal of Ultrasonics Ferroelectrics and Frequency ControlJan 1, 20260 citations

Nonlinear Spectroscopy

Wolfgang Demtröder

Springer eBooksJan 1, 20154 citations

VCSELs for Atomic Sensors.

Darwin K. Serkland

A new generation of small low-power atomic sensors, including clocks, magnetometers, and gyroscopes, is being developed based on recently available MEMS and VCSEL technologies.These sensors rely on spectroscopic interrogation of alkali atoms, typically rubidium or cesium, contained in small vapor cells.The relevant spectroscopic wavelengths (in vacuum) are 894.6 nm (D1) and 852.3 nm (D2) for cesium, and 795.0 nm (D1) and 780.2 nm (D2) for rubidium.The D1 wavelengths are either preferred or required, depending on the application, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources because of their low power consumption and circular output beam.This paper describes the required VCSEL characteristics for atomic clocks and magnetometers.The fundamental VCSEL requirement is single-frequency output with tunability to the particular spectroscopic line of interest.Singlepolarization and single-transverse-mode operation are implicit requirements.VCSEL amplitude noise and frequency noise are also important because they contribute significantly to the sensor signal-to-noise ratio.Additional desired VCSEL attributes are low cost, low power consumption, and several years of continuous operating lifetime.This paper also describes the 894-nm VCSELs that we have developed for cesium-based atomic sensors.In particular, we discuss VCSEL noise measurements and accelerated lifetime testing.Finally, we report the performance of prototype atomic clocks employing VCSELs.A new generation of small low-power atomic sensors, including clocks, magnetometers, and gyroscopes, is being developed based on recently available MEMS and VCSEL technologies.These sensors rely on spectroscopic interrogation of alkali atoms, typically rubidium or cesium, contained in small vapor cells.The relevant spectroscopic wavelengths (in vacuum) are 894.6 nm (D1) and 852.3 nm (D2) for cesium, and 795.0 nm (D1) and 780.2 nm (D2) for rubidium.The D1 wavelengths are either preferred or required, depending on the application, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources because of their low power consumption and circular output beam.This paper describes the required VCSEL characteristics for atomic clocks and magnetometers.The fundamental VCSEL requirement is single-frequency output with tunability to the particular spectroscopic line of interest.Singlepolarization and single-transverse-mode operation are implicit requirements.VCSEL amplitude noise and frequency noise are also important because they contribute significantly to the sensor signal-to-noise ratio.Additional desired VCSEL attributes are low cost, low power consumption, and several years of continuous operating lifetime.This paper also describes the 894-nm VCSELs that we have developed for cesium-based atomic sensors.In particular, we discuss VCSEL noise measurements and accelerated lifetime testing.Finally, we report the performance of prototype atomic clocks employing VCSELs.

Jul 26, 20160 citations

Nonlinear Spectroscopy

Wolfgang Demtröder

Laser SpectroscopyJan 1, 19964 citations

Nonlinear Spectroscopy

Laser SpectroscopyJul 22, 20082 citations

Quantum noise and polarization properties of vertical-cavity surface-emitting lasers

Jean-Luc C. Vey, Christian Degen, Karsten Auen +1 more

We present theoretical and experimental results on the quantum noise performances of vertical-cavity-surface-emitting-lasers (VCSELs). Using a semiclassical laser noise approach, we demonstrate that the ratio $M=\overline{S}/\overline{P}$ of the powers in the two polarization modes of the laser is one of the essential parameters governing the VCSELs quantum noise behavior. The generation of amplitude squeezed states of light is only possible for two well-selected cases which are the ideal two-polarization-mode laser $(M\ensuremath{\approx}1)$ and the ideal single-polarization-mode laser $(M\ensuremath{\approx}0),$ respectively. Furthermore, we show that gain suppression, as well as other relevant semiconductor parameters, have also to be taken into account to model realistically the VCSEL's quantum noise. These theoretical investigations are very well supported by our experimental results. We demonstrate experimentally that indeed there exists a direct link between the parameter M and the shot noise normalized amplitude noise. In a two-polarization-mode laser as, e.g., represented by a large diameter air-post VCSEL, squeezed states could not be generated because of insufficiently low values of M even though a strong anticorrelation between the two modes exists. With a single-polarization-mode laser, as realized with small diameter oxide confined VCSELs, we have been able to demonstrate the generation of single-mode squeezed light with a VCSEL. A squeezing level of 0.9 dB has been measured, which with the detection efficiency corrected, results in 1.3 dB at the VCSEL upper facet.We present theoretical and experimental results on the quantum noise performances of vertical-cavity-surface-emitting-lasers (VCSELs). Using a semiclassical laser noise approach, we demonstrate that the ratio $M=\overline{S}/\overline{P}$ of the powers in the two polarization modes of the laser is one of the essential parameters governing the VCSELs quantum noise behavior. The generation of amplitude squeezed states of light is only possible for two well-selected cases which are the ideal two-polarization-mode laser $(M\ensuremath{\approx}1)$ and the ideal single-polarization-mode laser $(M\ensuremath{\approx}0),$ respectively. Furthermore, we show that gain suppression, as well as other relevant semiconductor parameters, have also to be taken into account to model realistically the VCSEL's quantum noise. These theoretical investigations are very well supported by our experimental results. We demonstrate experimentally that indeed there exists a direct link between the parameter M and the shot noise normalized amplitude noise. In a two-polarization-mode laser as, e.g., represented by a large diameter air-post VCSEL, squeezed states could not be generated because of insufficiently low values of M even though a strong anticorrelation between the two modes exists. With a single-polarization-mode laser, as realized with small diameter oxide confined VCSELs, we have been able to demonstrate the generation of single-mode squeezed light with a VCSEL. A squeezing level of 0.9 dB has been measured, which with the detection efficiency corrected, results in 1.3 dB at the VCSEL upper facet.

Physical Review AOct 1, 199930 citations

M=\overline{S}/\overline{P}

of the powers in the two polarization modes of the laser is one of the essential parameters governing the VCSELs quantum noise behavior. The generation of amplitude squeezed states of light is only possible for two well-selected cases which are the ideal two-polarization-mode laser $(M\ensuremath{\approx}1)$ and the ideal single-polarization-mode laser $(M\ensuremath{\approx}0),$ respectively. Furthermore, we show that gain suppression, as well as other relevant semiconductor parameters, have also to be taken into account to model realistically the VCSEL's quantum noise. These theoretical investigations are very well supported by our experimental results. We demonstrate experimentally that indeed there exists a direct link between the parameter M and the shot noise normalized amplitude noise. In a two-polarization-mode laser as, e.g., represented by a large diameter air-post VCSEL, squeezed states could not be generated because of insufficiently low values of M even though a strong anticorrelation between the two modes exists. With a single-polarization-mode laser, as realized with small diameter oxide confined VCSELs, we have been able to demonstrate the generation of single-mode squeezed light with a VCSEL. A squeezing level of 0.9 dB has been measured, which with the detection efficiency corrected, results in 1.3 dB at the VCSEL upper facet.