分类： 天文学 >> 天文学 提交时间： 2023-02-19
Nemanja Jovanovic
Pradip Gatkine
Boqiang Shen
Maodong Gao
Nick Cvetojevic
Katarzyna Lawniczuk
Ronald Broeke
Charles Beichman
Stephanie Leifer
Jeffery Jewell
Gautam Vasisht
Dimitri Mawet
摘要： Spectral shaping is critical to many fields of science. In astronomy for example, the detection of exoplanets via the Doppler effect hinges on the ability to calibrate a high resolution spectrograph. Laser frequency combs can be used for this, but the wildly varying intensity across the spectrum can make it impossible to optimally utilize the entire comb, leading to a reduced overall precision of calibration. To circumvent this, astronomical applications of laser frequency combs rely on a bulk optic setup which can flatten the output spectrum before sending it to the spectrograph. Such flatteners require complex and expensive optical elements like spatial light modulators and have non-negligible bench top footprints. Here we present an alternative in the form of an all-photonic spectral shaper that can be used to flatten the spectrum of a laser frequency comb. The device consists of a circuit etched into a silicon nitride wafer that supports an arrayed-waveguide grating to disperse the light over hundreds of nanometers in wavelength, followed by Mach-Zehnder interferometers to control the amplitude of each channel, thermo-optic phase modulators to phase the channels and a second arrayed-waveguide grating to recombine the spectrum. The demonstrator device operates from 1400 to 1800 nm (covering the astronomical H band), with twenty 20 nm wide channels. The device allows for nearly 40 dBs of dynamic modulation of the spectrum via the Mach-Zehnders , which is greater than that offered by most spatial light modulators. With a superluminescent diode, we reduced the static spectral variation to ~3 dB, limited by the properties of the components used in the circuit and on a laser frequency comb we managed to reduce the modulation to 5 dBs, sufficient for astronomical applications.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Zhiquan Yuan
Heming Wang
Peng Liu
Bohan Li
Boqiang Shen
Maodong Gao
Lin Chang
Warren Jin
Avi Feshali
Mario Paniccia
John Bowers
Kerry Vahala
摘要： Narrow-linewidth lasers are important to many applications spanning precision metrology to sensing systems. Characterization of these lasers requires precise measurements of their frequency noise spectra. Here we demonstrate a correlated self-heterodyne (COSH) method capable of measuring frequency noise as low as 0.01 Hz^2/Hz at 1 MHz offset frequency. The measurement setup is characterized by both commercial and lab-built lasers, and features low optical power requirements, fast acquisition time and high intensity noise rejection.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Jingwei Ling
Jeremy Staffa
Heming Wang
Boqiang Shen
Lin Chang
Usman A. Javid
Lue Wu
Zhiquan Yuan
Raymond Lopez-Rios
Mingxiao Li
Yang He
Bohan Li
John E. Bowers
Kerry J. Vahala
Qiang Lin
摘要： High coherence visible and near-visible laser sources are centrally important to the operation of advanced position/navigation/timing systems as well as classical/quantum sensing systems. However, the complexity and size of these bench-top lasers is an impediment to their transitioning beyond the laboratory. Here, a system-on-a-chip that emits high-coherence visible and near-visible lightwaves is demonstrated. The devices rely upon a new approach wherein wavelength conversion and coherence increase by self-injection-locking are combined within in a single nonlinear resonator. This simplified approach is demonstrated in a hybridly-integrated device and provides a short-term linewidth around 10-30 kHz. On-chip, converted optical power over 2 mW is also obtained. Moreover, measurements show that heterogeneous integration can result in conversion efficiency higher than 25% with output power over 11 mW. Because the approach uses mature III-V pump lasers in combination with thin-film lithium niobate, it can be scaled for low-cost manufacturing of high-coherence visible emitters. Also, the coherence generation process can be transferred to other frequency conversion processes including optical parametric oscillation, sum/difference frequency generation, and third-harmonic generation.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Maodong Gao
Qi-Fan Yang
Qing-Xin Ji
Heming Wang
Lue Wu
Boqiang Shen
Junqiu Liu
Guanhao Huang
Lin Chang
Weiqiang Xie
Su-Peng Yu
Scott B. Papp
John E. Bowers
Tobias J. Kippenberg
Kerry J. Vahala
摘要： Optical microresonators with high quality (Q) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator Q factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of Q, the ultimate attainable Q, as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited Q factors in several photonic material platforms. High-Q microresonators are fabricated from thin films of SiO_2, Si_3N_4, Al_{0.2}Ga_{0.8}As and Ta_2O_5. By using cavity-enhanced photothermal spectroscopy, the material-limited Q is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate Q vary in a complementary fashion across photonic materials. Besides guiding microresonator design and material development in four material platforms, the results help establish performance limits in future photonic integrated systems.
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