Advances in laser spectroscopy have enabled many scientific breakthroughs in physics, chemistry, biology, and astronomy. Optical frequency combs pushed measurement limits with ultrahigh-frequency accuracy and fast-measurement speed, while tunable-diode-laser spectroscopy is used in scenarios that require high power and continuous spectral coverage. Despite these advantages of tunable-diode-laser spectroscopy, it is challenging to precisely determine the instantaneous laser frequency because of fluctuations in the scan speed. Here, we demonstrate a simple spectroscopy scheme with a frequency-modulated diode laser that references the laser on-the-fly to a fiber cavity. The fiber cavity’s free spectral range is on-the-fly calibrated with sub-10-Hz frequency precision. We achieve a relative precision of the laser frequency of 2×10−8 for an 11-THz frequency range at a measurement speed of 1 THz/s. This is an improvement of more than 2 orders of magnitude compared to existing diode-laser-spectroscopy methods. Our scheme provides precise frequency calibration markers, while simultaneously tracking the instantaneous scan speed of the laser. We demonstrate the versatility of our method through various applications, including dispersion measurement of a fiber, ultrahigh-Q microresonators, and spectroscopy of a hydrogen fluoride gas cell. The simplicity, robustness, and low cost of this spectroscopy scheme are valuable for out-of-the-lab applications like lidar and environmental monitoring.
Amplification of ultrafast optical pulses is key to a large number of applications in photonics. While ultrashort pulse amplification is well established in optical gain fibers, it is challenging to achieve in photonic-chip integrated waveguides, due to their inherent high-optical nonlinearity.
Here, we demonstrate for the first-time femtosecond pulse amplification on an integrated photonic chip. Our approach translates the concept of chirped pulse amplification to the chip level. Specifically, we leverage tailored all-normal dispersion, large mode-area gain waveguides to realize a low-nonlinearity, high-gain, short-length optical amplifier in which pulse propagation is dominated by dispersion. We show more than 17dB amplification of ultrashort pulses from a 1 GHz femtosecond source at center wavelength of 1815 nm. The amplified pulses have an on-chip output pulse peak power of 800 W with a pulse duration of 116 fs.
In this work, we evaluate the advantages and limitations of the Selective Laser-induced Etching (SLE) process for the fabrication of novel three-dimensional microresonator structures. Microresonators are resonant optical structures with the ability to store light of a specific wavelength. They are used as non-linear optical components, in sensors or even in integrated photonic devices. These structures are characterized by the optical quality factor Q as a measure of the optical storage capabilities. Q is significantly influenced by a high-quality optical surface with low surface roughness. In addition to surface quality and small dimensions, from tens of microns to millimeters, high optical nonlinearity is a key requirement in these fields. The fabrication of 3D fused silica parts fulfilling these requirements is an ongoing challenge in the field of microfabrication in quantum technology. The SLE process is used to fabricate three-dimensional parts of transparent materials such as fused silica with a high degree of geometric freedom in a two-step process. In the first step, a model of the part is written into the material using Ultrashort Pulse (USP) laser radiation. In the second step, the laser-written shape is wet-chemically etched in aqueous KOH to expose the part. The fabrication of 2D disk microresonators with high Q-factors is evaluated by studying the surface roughness of the SLE process followed by polishing. The polished samples are characterized and Q-factors >107 are achieved. In addition, the extent to which dimensions and geometry differ between design and real SLE components is analyzed. The SLE process will thus be investigated as a possible process for the future fabrication of three-dimensional microresonators.
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