Feed-forward comb-assisted coherence transfer to a widely tunable DFB diode laser.

The transfer of phase coherence from an ultrastable master laser to a distributed feedback diode laser, using an optical comb as a transfer oscillator, is obtained via a new scheme allowing continuous scanning across the whole tuning range of the slave laser together with absolute frequency determination. This is accomplished without phase lock loops, through a robust high-bandwidth feed-forward control acting directly on the slave laser output radiation. The correction is obtained by means of a dual-parallel Mach-Zehnder interferometer used as an optical single-sideband modulator. Coherence transfer across a master-slave frequency gap of 14 THz yields an ∼10 kHz linewidth providing high injection efficiency of an optical cavity with finesse 250 000. This allows demonstrating a cavity ring-down absorption spectrum of low-pressure ambient air over a 300 GHz spectral window.

Wide-bandwidth Pound-Drever-Hall locking through a single-sideband modulator.

An integrated single-sideband modulator is used as the sole wide-bandwidth frequency actuator in a Pound-Drever-Hall locking loop. Thanks to the large modulation bandwidth, the device enables a locking range of ±75 MHz and a control bandwidth of 5 MHz without the need for a second feedback loop. As applied to the coupling of an extended-cavity diode laser at 1.55 µm to a high-finesse optical cavity, the in-loop frequency noise spectral density reaches a minimum of 1 mHz/Hz(1/2) at 1 kHz.

Communication: Saturated CO2 absorption near 1.6 µm for kilohertz-accuracy transition frequencies.

Doppler-free saturated-absorption Lamb dips were measured on weak rovibrational lines of (12)C(16)O2 between 6189 and 6215 cm(-1) at sub-Pa pressures using optical feedback frequency stabilized cavity ring-down spectroscopy. By referencing the laser source to an optical frequency comb, transition frequencies for ten lines of the 30013←00001 band P-branch and two lines of the 31113←01101 hot band R-branch were determined with an accuracy of a few parts in 10(11). Involving rotational quantum numbers up to 42, the data were used for improving the upper level spectroscopic constants. These results provide a highly accurate reference frequency grid over the spectral interval from 1599 to 1616 nm.

Optical phase cloning by an integrated dual-parallel Mach-Zehnder modulator.

The use of a dual-parallel Mach-Zehnder modulator in a feed-forward configuration is shown to serve the purpose of cloning the optical phase of a master oscillator on a distributed-feed-back (DFB) slave laser exhibiting a multi-MHz-wide frequency noise spectrum. A residual phase error of 113 mrad is obtained together with an extremely high control bandwidth of hundreds of megahertz and a gigahertz-level capture and tuning range. Besides offering a dramatic improvement over feedback loops, this approach is susceptible of hybrid integration in a cost-effective compact device benefiting from the wide tunability of DFB lasers.

Comb-locked cavity ring-down spectrometer.

Extreme frequency accuracy and high sensitivity are obtained with a novel comb-locked cavity-ring-down spectrometer operating in the near-infrared from 1.5 to 1.63 µm. A key feature of our approach is the tight frequency locking of the probe laser to the comb, ensuring very high reproducibility and accuracy to the frequency axis upon scanning the comb repetition rate, as well as an efficient light injection into a length-swept high-finesse passive cavity containing the gas sample. Spectroscopic tests on the (30012) ← (00001) P14e line of CO2 at ∼1.57 µm demonstrate an accuracy of ∼17 kHz on the line center frequency in a Doppler broadening regime over the time scale of about 5 min, corresponding to four consecutive spectral scans of the absorption line. Over a single scan, which consists of 1500 spectral points over 75 s, the limit of detection is as low as 5.7 × 10(-11) cm(-1).

Frequency-stabilized 1 W optical comb at 2.2-2.6 µm by Cr2+:ZnSe multipass amplification.

We present a frequency comb source with power level up to 150 µW per comb mode, tunable in the 2.2-2.6 µm wavelength region, based on a Cr(2+):ZnSe multipass solid-state amplifier seeded by the output of an actively stabilized optical parametric oscillator, synchronously pumped by a commercial 250 MHz Er:fiber laser. Phase relationship between idler, signal, and pump waves is exploited to perform frequency comb stabilization in the whole 2.2-2.6 µm mid-infrared spectral region.