RESUMO
Second-harmonic generation allows for coherently bridging distant regions of the optical spectrum, with applications ranging from laser technology to self-referencing of frequency combs. However, accessing the nonlinear response of a medium typically requires high-power bulk sources, specific nonlinear crystals, and complex optical setups, hindering the path toward large-scale integration. Here we address all of these issues by engineering a chip-scale second-harmonic (SH) source based on the frequency doubling of a semiconductor laser self-injection-locked to a silicon nitride microresonator. The injection-locking mechanism, combined with a high-Q microresonator, results in an ultra-narrow intrinsic linewidth at the fundamental harmonic frequency as small as 41 Hz. Owing to the extreme resonant field enhancement, quasi-phase-matched second-order nonlinearity is photoinduced through the coherent photogalvanic effect and the high coherence is mapped on the generated SH field. We show how such optical poling technique can be engineered to provide efficient SH generation across the whole C and L telecom bands, in a reconfigurable fashion, overcoming the need for poling electrodes. Our device operates with milliwatt-level pumping and outputs SH power exceeding 2 mW, for an efficiency as high as 280%/W under electrical driving. Our findings suggest that standalone, highly-coherent, and efficient SH sources can be integrated in current silicon nitride photonics, unlocking the potential of χ(2) processes in the next generation of integrated photonic devices.
RESUMO
A system for gas sensing based on the quartz-enhanced photoacoustic spectroscopy technique has been developed. It makes use of a quantum well distributed feedback (DFB) laser diode emitting at 3.38 µm. This laser emits near room temperature in the continuous wave regime. A spectrophone, consisting of a quartz tuning fork and two steel microresonators were used. Second derivative wavelength modulation detection is used to perform low concentration measurements. The sensitivity and the linearity of the Quartz enhanced photoacoustic spectroscopy (QEPAS) sensor were studied. A normalized noise equivalent absorption coefficient of 4.06×10(-9) cm(-1)·W/Hz(1/2) was achieved.
RESUMO
The mid-IR region beyond 3 microm is very attractive for gas sensing, since the fundamental absorption bands of several hydrocarbons are located in this range. We demonstrated, for the first time to our knowledge, the use of a novel GaInAsSb/AlGaInAsSb distributed-feedback laser emitting around 3.03 microm in a tunable-diode laser-spectroscopy application. The laser operates in continuous mode at room temperature with excellent single-mode and tuning properties. A comparison of the measurement results was made with the recently updated data on C212H(2) found in the HITRAN 2008 compilation. A good agreement was found between the measurements and the database. Wavelength modulation spectroscopy of acetylene at ambient conditions was made, and a sensitivity of 18 ppb (parts per billion) per meter at an integration time of 3 s corresponding to a relative absorption of 5 x 10(-6) was obtained. The optimum detection limit of the acetylene measurement in this wavelength modulation spectroscopy setup was better than 1.5 ppb m at an integration time of 600 seconds.