David Larsson

Low-jitter and high-power 40-GHz all-active mode-locked lasers

A novel design strategy for the epitaxial structure of monolithic mode-locked semiconductor lasers is presented. Using an all-active design, we fabricate 40-GHz lasers generating 2.8-ps almost chirp-free pulses with record low high-frequency jitter and more than 7-mW fiber coupled output power.

Self-mixing interferometry in vertical-cavity surface-emitting lasers for nanomechanical cantilever sensing

We have experimentally investigated self-mixing interference produced by the feedback of light from a polymer micrometer-sized cantilever into a vertical-cavity surface-emitting laser for sensing applications. In particular we have investigated how the visibility of the optical output power and the junction voltage depends on the laser injection current and the distance to the cantilever. The highest power visibility obtained from cantilevers without reflective coatings was ∼60%, resulting in a very high sensitivity of 45 mV/nm with a noise floor below 1.2 mV. Different detection schemes are discussed.

Thermoplastic microcantilevers fabricated by nanoimprint lithography

Nanoimprint lithography has been exploited to fabricate micrometre-sized cantilevers in thermoplastic. This technique allows for very well defined microcantilevers and gives the possibility of embedding structures into the cantilever surface. The microcantilevers are fabricated in TOPAS and are up to 500 µm long, 100 µm wide, and 4.5 µm thick. Some of the cantilevers have built-in ripple surface structures with heights of 800 nm and pitches of 4 µm. The yield for the cantilever fabrication is 95% and the initial out-of-plane bending is below 10 µm. The stiffness of the cantilevers is measured by deflecting the cantilever with a well-characterized AFM probe. An average stiffness of 61.3 mN m−1 is found. Preliminary tests with water vapour indicate that the microcantilevers can be used directly for vapour sensing applications and illustrate the influence of surface structuring of the cantilevers.

Low-noise monolithic mode-locked semiconductor lasers through low-dimensional structures

The design of a quantum well (QW) based high-saturation energy and low-loss gain region allows a high power density which ensures efficient saturation of the absorber, increases the efficiency, and lowers the noise of monolithic modelocked lasers. This is illustrated though 10 GHz all-active lasers with different number of quantum wells. By comparing a 40 GHz quantum dot and a 40 GHz quantum well laser we discuss the physical difference in the dynamics of the devices. The slow dynamics of quantum dots (QD), results in low self-phase modulation for picosecond pulses and a strong damping of intensity fluctuations, which gives rise to clean optical spectra and very low noise for passive mode-locking.

41 GHz and 10.6 GHz low threshold and low noise InAs/InP quantum dash two-section mode-locked lasers in L band

This paper reports recent results on InAs/InP quantum dash–based, two-section, passively mode-locked lasers pulsing at 41 GHz and 10.6 GHz and emitting at 1.59 μm at 20 °C. The 41-GHz device (1 mm long) starts lasing at 25 mA under uniform injection and the 10.6 GHz (4 mm long) at 71 mA. Their output pulses are significantly chirped. The 41-GHz laser exhibits 7 ps pulses after propagation in 60 m of a single-mode fiber. The 10.6-GHz laser generates one picosecond pulses with 545 m of a single-mode fiber. Its single side-band phase noise does not exceed –80 dBc/Hz at 100 kHz offset, leading to an average timing jitter of 800 fs.

Long All-Active Monolithic Mode-Locked Lasers With Surface-Etched Bragg Gratings

We have fabricated 4.4-mm-long monolithic InAlGaAsP-InP mode-locked lasers with integrated deeply surface etched distributed Bragg reflector (DBR) mirrors. The lasers produce 3.7-ps transform-limited Gaussian pulses with 10-mW average output power and 250-fs absolute timing jitter. The performance of the DBR lasers is compared to the performance of Fabry-Perot mode-locked lasers from the same wafer and to the performance of earlier reported long monolithic DBR mode-locked lasers and is found to be better.

Optimization of VCSELs for Self-Mixing Sensing

We have simulated the variations in optical output power from a vertical-cavity surface-emitting laser (VCSEL) subject to self-mixing feedback, which is very important for applications in sensing. In order to maximize the self-mixing signal for a given feedback we have optimized the epitaxial design of the VCSEL. The most important parameters are the number of quantum wells (gain), the number of Bragg mirrors (reflection), and the detector position.

Design and evaluation of mode-locked semiconductor lasers for low noise and high stability (Invited Paper)

We present work on design of monolithic mode-locked semiconductor lasers with focus on the gain medium. The use of highly inverted quantum wells in a low-loss waveguide enables both low quantum noise, low-chirped pulses and a large stability region. Broadband noise measurements are performed and used to confirm the design principles.

Polymer-coated vertical-cavity surface-emitting laser diode vapor sensor

We report a new method for monitoring vapor concentration of volatile organic compounds using a vertical-cavity surface-emitting laser (VCSEL). The VCSEL is coated with a polymer thin film on the top distributed Bragg reflector (DBR). The analyte absorption is transduced to the electrical domain through modulation of the VCSEL output power as the polymer swell. We have investigated the responsivity of this technique experimentally using a plasma polymerized polystyrene coating and explain the results theoretically as a reflectance modulation of the top DBR.

10-GHz 1.59-μm quantum dash passively mode-locked two-section lasers

This paper reports the fabrication and the characterisation of a 10 GHz two-section passively mode-locked quantum dash laser emitting at 1.59 μm. The potential of the devices mode-locking is investigated through an analytical model taking into account both the material parameters and the laser geometry. Results show that the combination of a small absorbing section coupled to a high absorption coefficient can lead to an efficient mode-locking. Characterisation shows mode-locking operation though output pulses are found to be strongly chirped. Noise measurements demonstrate that the single side band phase noise does not exceed -80 dBc/Hz at 100 kHz offset leading to an average timing jitter as low as 800 fs. As compared to single QW lasers these results constitute a significant improvement and are of first importance for applications in optical telecommunications.