Stefan Kundermann

Self-referenceable frequency comb from a gigahertz diode-pumped solid-state laser

We present carrier envelope offset (CEO) frequency detection of a diode-pumped Yb:KGW (ytterbium-doped potassium gadolinium tungstate) laser with a repetition rate of 1 GHz. The SESAM-soliton-modelocked laser delivers 2.2-W average power in 290-fs pulses. This corresponds to a peak power of 6.7 kW and the optical-to-optical efficiency is 38%. With a passive pulse compression the duration is reduced to 100 fs at an average power of 1.1 W. Coherent supercontinuum (SC) generation in a highly nonlinear photonic crystal fiber (PCF) is achieved without additional amplification. Furthermore we have demonstrated that pulse compression towards lower soliton orders of approximately 10 was required for coherent SC generation and CEO detection. Additional numerical simulations further confirm these experimental results.

Radiation hard mode-locked laser suitable as a spaceborne frequency comb

We report ground-level gamma and proton radiation tests of a passively mode-locked diode-pumped solid-state laser (DPSSL) with Yb:KYW gain medium. A total gamma dose of 170 krad(H(2)O) applied in 5 days generates minor changes in performances while maintaining solitonic regime. Pre-irradiation specifications are fully recovered over a day to a few weeks timescale. A proton fluence of 9.76·10(10) cm(-2) applied in few minutes shows no alteration of the laser performances. Furthermore, complete stabilization of the laser shows excellent noise properties. From our results, we claim that the investigated femtosecond DPSSL technology can be considered rad-hard and would be suitable for generating frequency combs compatible with long duration space missions.

Repetition rate stabilization of an optical frequency comb based on solid-state laser technology with an intra-cavity electro-optic modulator

The repetition rate stabilization of an optical frequency comb based on diode-pumped solid-state laser technology is demonstrated using an intra-cavity electro-optic modulator. The large feedback bandwidth of such modulators allows disciplining the comb repetition rate on a cavity-stabilized continuous-wave laser with a locking bandwidth up to 700 kHz. This surpasses what can be achieved with any other type of actuator reported so far. An in-loop integrated phase noise of 133 mrad has been measured and the PM-to-AM coupling of the electro-optic modulator has been investigated as well.

Comparison of different carrier-envelope frequency stabilization methods for a high performance DPSSL frequency comb

Carrier envelope frequency (fCEO) stabilization of frequency combs is traditionally achieved via power modulation of the pump of the comb oscillator. A further possibility is to shift the laser fCEO using an external acousto-optic frequency shifter (AOFS). In this case the optical frequency comb spectrum is shifted exactly by the RF modulation frequency of the AOFS. In this work different stabilization schemes in self-referenced frequency comb system architecture are compared. It is shown that AOFS frequency shifting represents a high performance alternative to the standard feedback control via pump power modulation.

Compact Gigahertz Frequency Comb Generation: How Short Do The Pulses Need To Be?

We investigate the required pulse duration for coherent supercontinuum generation for CEO detection in the 1-µm and 1.5-µm spectral regime. We demonstrate the first self-referenceable frequency comb from a gigahertz diode-pumped solid state laser.

High-pulse energy-stabilized passively mode-locked external cavity inverse bow-tie 990nm laser diode for space applications

We report on multi-section inverse bow-tie laser producing mode-locked pulses of 90 pJ energy and 6.5 ps width (895 fs after compression) at 1.3 GHz pulse repetition frequency (PRF) and consuming 2.9 W of electric power. The laser operates in an 80 mm long external cavity. By translation of the output coupling mirror, the PRF was continuously tuned over 37 MHz range without additional adjustments. Active stabilization with a phase lock loop actuating on the driving current has allowed us to reach the PRF relative stability at a 2·10-10 level on 10 s intervals, as required by the European Space Agency (ESA) for inter-satellite long distance measurements.

On-chip integrated zero-RAM frequency modulator for noise reduction and linewidth narrowing in discrete-mode lasers

Wavelength tuneable lasers for 40G and 100G coherent optical communications systems need to meet stringent requirements on narrow linewidth emission across the entire tuning range, with typical values of 300–500 kHz required in commercial systems. Higher capacities can be achieved in next generation systems by employing higher order modulation formats such as 16QAM or 64QAM. However, such systems have even more stringent linewidth requirements [1]. For example, square 64QAM transmission at data rate 40Gbit/s (the baud rate is 6.7G symbols / second) demands a laser with 1 kHz linewidth. Although linewidths as low as 70 kHz and even lower have been demonstrated in free-running Discrete Mode Laser Diodes (DMLD), further (active) linewidth reduction is required. This can be achieved by introducing a phase modulator on chip and applying a Pound-Drever-Hall (PDH) technique to stabilize on an optical reference cavity for instance. In the usual implementation of the PDH technique an external acousto-optic modulator (AOM) is used for active phase noise correction (Figure 1 (a), compare blue and red curves). This worsens significantly the intensity noise (Figure 1 (b)) rendering the laser unsuitable for QAM applications. In this talk we will report a DMLD laser with on-chip integrated frequency modulator based on Joule heating and showing zero residual amplitude modulation (RAM) (Figure 1 (a) and (b) green curves show preliminary stabilization results). DMLDs with integrated phase modulators are highly interesting for coherent optical communications and other applications demanding actively narrowed linewidth emission while offering an economic approach with a focus on high volume manufacturability of monolithic semiconductor lasers [2].

9.6 GHz ultra-low phase noise signal generation from a diode-pumped solid-state laser

We present ultra-low phase noise microwave generation based on a photonics oscillator. By using an ultra-narrow linewidth continuous-wave laser stabilized on a high-finesse optical cavity as a frequency reference, an optical frequency comb as an optical-to-microwave frequency divider and a photodiode for optical-to-electrical conversion, a 9.6 GHz carrier frequency signal has been generated with residual phase noise of -110 dBc/Hz and absolute phase noise below -165 dBc/Hz at 1 Hz and 1 MHz offset frequencies respectively. Further improvements of the system are under way.

Low-noise 1-micron optical frequency comb based on diode-pumped solid-state laser technology

Optical frequency combs are key instruments that have revolutionized many fields like frequency metrology and spectroscopy. Traditionally based on fiber lasers or Ti:Sapphire lasers they have been widely studied. Here we demonstrate a 1-micron optical frequency comb based on passively mode-locked diode-pumped solid-state laser technology with low-noise properties and high-reliability.

Compact Hz-level linewidth laser system

Increasing the compactness and robustness of laser stabilization systems is a critical need for the development of industrial applications of ultra-narrow linewidth lasers. In this aim, a compact optical setup based on the Pound-Drever-Hall scheme with a high finesse cavity was built with overall dimensions of L × W × H = 45 × 35 × 13 cm³. An external cavity diode laser (PLANEX^™, RIO Inc.) as well as a distributed-feedback fiber laser (Koheras Adjustik, NKT photonics) were stabilized using this system. The frequency stability was evaluated using a similar setup as reference. The combined relative stability of the systems reached 7·10⁻¹⁵ at 1s.