Michel Lintz

All-Fibered High-Quality Stable 20- and 40-GHz Picosecond Pulse Generators for 160-Gb/s OTDM Applications

In this work, we investigate the generation of stable 20- and 40-GHz pulse trains through the nonlinear compression of an initial beat-signal in a cavity-less optical-fiber-based device. Enhanced temporal stability is achieved by generating the sinusoidal beating thanks to a commercial LiNbO3 intensity modulator driven by a half repetition-rate external radio-frequency (RF) clock. We also show that the residual timing jitter induced by the RF phase modulation imposed to suppress Brillouin back-scattering can be reduced by managing the cumulated dispersion of the compression line, whereas complete polarization stabilization is obtained owing to a modified setup involving a Faraday rotator mirror. Finally, a high-quality 160-Gb/s signal is generated from our low duty-cycle 40-GHz pulse source through optical time-division multiplexing (OTDM).

Demonstration of an optical polarization magnifier with low birefringence

In any polarimetric measurement technique, enhancing the laser polarization change of a laser beam before it reaches the analyzer can help in improving the sensitivity. Enhancement of a small polarization rotation can be performed using an optical component having a large linear dichroism, the enhancement factor being equal to the square root of the ratio of the two transmission factors. A pile of parallel plates at Brewster incidence seems appropriate for realizing such a polarization magnifier. In this article, we address the problem raised by the interference in the plates and between the plates, which affects the measurement by giving rise to birefringence. We demonstrate that wedged plates provide a convenient and efficient way to avoid this interference. We have implemented and characterized devices with four and six wedged plates at Brewster incidence, which have led to a decisive improvement of the signal-to-noise ratio in our ongoing parity violation measurement.

Pump-probe measurement of atomic parity violation in cesium with a precision of 2.6%

Abstract.We present the atomic parity violation measurements made in Cs vapour using a pump-probe scheme. After pulsed excitation of the 6S -7S forbidden transition in the presence of a longitudinal electric field, a laser beam resonant with one of the 7S -6P transitions stimulates the 7S atom emission for a duration of 20ns. The polarisation of the amplified probe beam is analysed. A seven-fold signature allows discrimination of the parity-violating linear dichroism, and real-time calibration by a similar, known, parity-conserving linear dichroism. The zero-field linear dichroism signal due to the magnetic dipole transition moment is observed for the first time, and used for in situ determination of the electric field. The result, ImE1pv = (- 808±21)×10-14ea0 , is in perfect agreement with the corresponding, more precise measurement obtained by the Boulder group. A transverse field configuration with large probe amplification could bring atomic parity violation measurements to the 0.1% accuracy level.

Phase Measurement of a Microwave Optical Modulation: Characterisation and Reduction of Amplitude-to-Phase Conversion in 1.5 μm High Bandwidth Photodiodes

High accuracy and low noise measurement of the phase of a microwave signal requires that spurious contributions are adequately dealt with. In this paper we investigate the power-to-phase coupling in two commercial high bandwidth P-I-N, near-IR photodetectors. We observe that a sudden change of the optical power induces a transient of the phase of the 20 GHz signal, at different time scales. The temperature rise of the photodetector junction is likely to be involved in this dynamical behaviour. The value of the bias voltage applied to the photodetector appears to control the size of the phase transients, as well as the optical power for which the slope of the amplitude-to-phase coupling cancels. The most efficient way to reduce amplitude to phase couplings consists in implementing optical demodulation, instead of electrical demodulation, of the microwave signal.

Comments and Corrections Comments on “Frequency Response of the Noise Conversion From Relative Intensity Noise to Phase Noise in the Photodetection of an Optical Pulse Train”

It is shown that the results presented in the above letter, and attributed by the authors to amplitude-to-phase conversion in the photodetector, do not originate in the photodetector under test, due to the power dependence observed. More recent results show that conversion effects with the same size and frequency dependence are observed in passively mode-locked nonlinear polarization rotation mode-locked lasers.

Alkali-vapor cell with metal coated windows for efficient application of an electric field

We describe the implementation of a cylindrical T-shaped alkali-vapor cell for laser spectroscopy in the presence of a longitudinal electric field. The two windows are used as two electrodes of the high-voltage assembly, which is made possible by a metallic coating which entirely covers the inner and outer sides of the windows except for a central area to let the laser beams in and out of the cell. This allows very efficient application of the electric field, up to 2kV∕cm in a rather dense superheated vapor, even when significant photoemission takes place at the windows during pulsed laser irradiation. The body of the cell is made of sapphire or alumina ceramic to prevent large currents resulting from surface conduction observed in cesiated glass cells. The technique used to attach the monocrystalline sapphire windows to the cell body causes minimal stress birefringence in the windows. In addition, reflection losses at the windows can be made very small. The vapor cell operates with no buffer gas and has ...

Note: Efficient diode laser line narrowing using dual, feed-forward + feed-back laser frequency control

We have achieved distributed feedback laser diode line narrowing by simultaneously acting on the diode current via a feed-back loop and on an external electrooptic phase modulator in feed-forward actuator. This configuration turns out to be very efficient in reaching large bandwidth in the phase correction: up to 15 MHz with commercial laser control units. About 98% of the laser power undergoes narrowing. The full width at half maximum of the narrowed optical spectrum is of less than 4 kHz. This configuration appears to be very convenient as the delay in the feed-forward control electronics is easily compensated for by a 20 m optical fiber roll.

A Two-mode Interference Measurement for Nanometer Accuracy Absolute Distance Ranging

We present a laser ranging system, under development, that uses a high frequency modulated beam to achieve sub-nm resolution by the combined use of interferometric and time-of-flight measurements. We first describe how the absolute distance is extracted from a two-mode interference signal. In particular we show that the signal, which presents both optical and synthetic wavelength scales, is essential to achieve nm-scale accuracy, despite the significant long-term phase drifts in the 20 GHz detection chains. Then we present results obtained with the telemeter implemented on an optical table, for a distance of about four meters, implemented by folding the laser beam path to the target. The challenge here is to achieve a phase and amplitude measurement of two 20 GHz signals with a resolution well below 10-4 cycle and 10-4, respectively, despite the fact that the signal undergoes very strong (×3 ) amplitude changes.

DUAL, FEED-FORWARD + FEED-BACK LASER FREQUENCY CONTROL FOR EFFICIENT AND CONVENIENT DIODE LASER LINE NARROWING

Distributed feedback (DFB) diode lasers are convenient, small footprint and robust single mode laser sources. DFB lasers have an emission linewidth in the MHz to several MHz range, which may be too large for some applications, such as cold atom physics, optical clocks, laser ranging, lidar or gas sensing... Control of the diode forward current allows for the control the frequency of the emitted laser beam.

On recent progress in all-fibered pulsed optical sources from 20 GHz to 2 THz based on multiple four wave mixing approach

In this paper, we report recent progress on the design of all-fibered ultra-high repetition-rate pulse sources for telecommunication applications around 1550 nm. Based on the nonlinear compression of an initial beat-signal in optical fibers through a multiple four-wave mixing process, we theoretically and experimentally demonstrate that this simple technique allows an efficient and accurate design of versatile pulse sources having repetition rates and pulse durations ranging from 20 GHz up to 2 THz and from 10 ps up to 110 fs, respectively.