Tightly locked optical frequency comb from a semiconductor disk laser.

Ultrafast semiconductor disk lasers (SDLs) passively modelocked using semiconductor saturable absorbers mirrors (SESAMs) generate optical frequency combs (OFCs) with gigahertz line spacings - a regime where solid-state and fiber lasers struggle with geometrical and Q-switching limitations. We stabilized both the frequency comb spacing and the offset without any additional external optical amplification or pulse compression. The overall noise performance is competitive with other gigahertz OFCs. A SESAM-modelocked vertical external-cavity surface-emitting laser (VECSEL) at a center wavelength around 1 µm generates 122-fs pulses with 160 mW average output power and we only needed 17-pJ pulse energy coupled into a silicon nitride (Si3N4) waveguide for supercontinuum generation (SCG) and OFC offset stabilization.

Direct thermo-optical tuning of silicon microresonators for the mid-infrared.

We use light from a visible laser diode to directly tune silicon-on-chip microresonators by thermo-optical effect. We show that this direct tuning is local, non invasive and has a much smaller time constant than global temperature tuning methods. Such an approach could prove to be highly effective for Kerr comb generation in microresonators pumped by quantum cascade lasers, which cannot be easily tuned to achieve comb generation and soliton-mode locked states.

Frequency comb offset detection using supercontinuum generation in silicon nitride waveguides.

We present the first direct carrier-envelope-offset (CEO) frequency detection of a modelocked laser based on supercontinuum generation (SCG) in a CMOS-compatible silicon nitride (Si(3)N(4)) waveguide. With a coherent supercontinuum spanning more than 1.5 octaves from visible to beyond telecommunication wavelengths, we achieve self-referencing of SESAM modelocked diode-pumped Yb:CALGO lasers using standard f-to-2f interferometry. We directly obtain without amplification strong CEO beat signals for both a 100-MHz and 1-GHz pulse repetition rate laser. High signal-to-noise ratios (SNR) of > 25 dB and even > 30 dB have been generated with only 30 pJ and 36 pJ of coupled pulse energy from the megahertz and gigahertz laser respectively. We compare these results to self-referencing using a commercial photonic crystal fiber and find that the required peak power for CEO beat detection with a comparable SNR is lowered by more than an order of magnitude when using a Si(3)N(4) waveguide.

Ultrabroadband supercontinuum generation in a CMOS-compatible platform.

We demonstrate supercontinuum generation spanning 1.6 octaves in silicon nitride waveguides. Using a 4.3 cm-long waveguide, with an effective nonlinearity of γ=1.2 W(-1) m(-1), we generate a spectrum extending from 665 nm to 2025 nm (at -30 dB) with 160 pJ pulses. Our results offer potential for a robust, integrated, and low-cost supercontinuum source for applications including frequency metrology, optical coherence tomography, confocal microscopy, and optical communications.