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Using the Jones formalism, it is shown that electro-optic modulators used for phase modulation generate a modulation of the output polarization induced by the difference of phase modulation depth along the crystallographic axes of the modulator. We study two consequences of this polarization modulation in the fiber setups, limiting the performance of high sensitivity measurement devices. The first one is its partial conversion into a residual amplitude modulation (RAM) within any component presenting polarization dependent losses (PDL). The second one is a new effect that consists of the distortion of the signal detected at the output of a fiber cavity. The theoretical expressions of the detected signals are computed in each case.

In this paper, we present an experimental study of the metrological stabilization of a solid-state frequency comb for embedded metrology applications. The comb is a passively mode-locked laser diode based on InGaAs/InP Quantum-dash structure emitting optical lines into a 9 nm bandwidth centered at 1.55 $\mu$m with a repetition rate of 10.09 GHz. The frequency stabilization is achieved by optical injection locking of the comb with an external cavity laser diode referenced onto a metrological frequency standard. One observes the transfer of the spectral purity from the injection laser to the neighbouring modes of the injected one as well as the transfer of stability to the adjacent modes. The measurement of the long term stability highlights a frequency noise with random walk behavior specific of the passive mode locking process. Demonstration of sidebands of the injection laser at the repetition frequency of the comb also makes it possible to propose a transfer mechanism and to consider a complete stabilization of the frequency comb at a metrological stability level.

We demonstrate a compact and low-cost all-fiber-based locking setup for frequency-noise suppression of a 420 nm external-cavity diode laser. Frequency noise reduction in the 100 Hz to 800 kHz range is demonstrated up to 40 dB associated with a linewidth narrowing from 850 kHz to 20 kHz for 10 ms integration time. This simple locking scheme might be implemented for a large range of wavelengths and can be integrated on a small footprint for embedded applications requiring narrow linewidth blue laser diodes.

We describe a fiber ring cavity for transferring frequency stability from a metrological optical reference at 1542 nm to tunable lasers covering 100 nm around 1.55 µm and show a stability transfer to the 10−15 level in relative value. The optical length of the ring is controlled by two actuators: a cylindrical piezoelectric tube (PZT) actuator on which a portion of the fiber is coiled and glued for fast corrections (vibrations) acting on the length of the fiber, and a Peltier module for slow corrections acting on its temperature. We characterize the stability transfer and analyze the limitations imposed by two critical effects in the setup: Brillouin backscattering and the polarization modulation generated by the electro-optic modulators (EOMs) used in the error signal detection scheme. We show that it is possible to reduce the impact of these limitations to a level below the detection threshold imposed by the servo noise. We also show that in the long term, the limitation to the stability transfer is a thermal sensitivity of –550 Hz/K/nm which could be reduced by active control of the ambient temperature.

In this paper we present recent results on a fiber ring cavity stabilization and some of its limitations such as polarization modulation, error signal line shape distortion due to residual amplitude modulation (RAM), intracavity backscattering and dispersion. Solutions for each limitative phenomenon are proposed. A stability transfer over 30 GHz at the 10-14 level is demonstrated which propose a possibility to perform successful frequency stability transfer over several nanometers.

We report in this communication experimental investigation on full frequency stabilization of a compact Frequency Comb. The Comb is an InGaAs Quantum-dot Fabry-Perot diode emitting about 150 modes spaced of 10 GHz into a 10 nm optical band around 1.55µm. Frequency stabilization of the comb carrier (f 0 ) is obtained thanks to optical injection leading to relative frequency stability at 10 -13 level. Stability transfer along the comb (f rep ) is studied by means of current electrical modulation (electrical injection at f rep ). Such frequency comb sources are of particular interest for transportable measuring systems, in fundamental physics, spectroscopy or clocks comparison [1] .

We present an experimental investigation of the stability limits specific to optical frequency standards using fiber optic architecture and semiconductor lasers. A compact setup composed of a semiconductor laser frequency-locked onto an acetylene transition detected in saturated absorption has been implemented using only fiber optic components. Fiber optic technology allows compact and reliable solutions for various applications. However, for high sensitivity and stability applications such as metrology, residual reflections induced by optical index inhomogeneities in connectors and fiber-coupled components leading to spurious interference significantly limit performance. We have examined the origin of the interference fringes superimposed on the detected signal and the limitations they cause to the frequency stability of the reference. The effects of temperature and beam power fluctuations are also examined. Our results show that the frequency stability is limited in the 10 − 13 range by the effect of interference fringes due to use of fiber components.

We analyse limitations introduced by a fibre connectorised Lithium-Niobate electro-optic modulator which modulates the beam of a1.5 μm laser for frequency lock onto one mode of a fibre cavity. It is shown that the ellipticity and/or misalignment of the input polarization with the main axes of the modulator leads to a modulation of the output polarization. This results in two effects on the signal detected at the cavity output: an offset due to residual amplitude modulation (RAM) and a distortion due to the slight birefringence presented by the cavity. Both effects limit the stability of the frequency lock.

The use of fibre-optical components allows the development of compact devices qualified for numerous industrial applications (telecoms, space, radar, etc.). However, some limitations due to the use of optical fibres are critical in a metrological context. The main limitation is the high sensitivity of the light polarization to environmental conditions as temperature and pressure. The second is the presence of interferences caused by residual reflections at the optical interfaces [1]. We present an original scheme to overcome those limitations while achieving metrological performances.

A compact setup for transferring the stability of a metrological frequency reference at 1.55 μm is described. One mode of a fiber-ring cavity is frequency-locked onto the reference. The stability transfer is achieved by locking an extended-cavity diode laser, tunable over 100 nm onto one cavity mode. Once locked, this tunable laser exhibits a relative frequency stability close to 10−12 for integration times from 1 to 3000 s (minimum of 6·10−13 at 10 s). We show that this stability limitation is due to the polarization fluctuations’ sensitivity of the fiber optic components. Using a second cavity, the frequency stability transfer over 58 nm is demonstrated at a level of 4·10−12. Associated with a local frequency reference and with an efficient acoustic and thermal insulation, this compact setup is intended for embedded metrological applications.