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
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$_3$N$_4$, Al$_{0.2}$Ga$_{0.8}$As and Ta$_2$O$_5$. 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.
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
Qing-Xin Ji
Warren Jin
Lue Wu
Yan Yu
Zhiquan Yuan
Wei Zhang
Maodong Gao
Bohan Li
Heming Wang
Chao Xiang
Joel Guo
Avi Feshali
Mario Paniccia
Vladimir S. Ilchenko
Andrey B. Matsko
John Bowers
Kerry Vahala
摘要： Normal group velocity dispersion (GVD) microcombs offer high comb line power and high pumping efficiency compared to bright pulse microcombs. The recent demonstration of normal GVD microcombs using CMOS-foundry-produced microresonators is an important step towards scalable production. However, the chromatic dispersion of CMOS devices is large and impairs generation of broadband microcombs. Here, we report the development of a microresonator in which GVD is reduced due to a couple-ring resonator configuration. Operating in the turnkey self-injection-locking mode, the resonator is hybridly integrated with a semiconductor laser pump to produce high-power-efficiency combs spanning a bandwidth of 9.9 nm (1.22 THz) centered at 1560 nm, corresponding to 62 comb lines. Fast, linear optical sampling of the comb waveform is used to observe the rich set of near-zero GVD comb behaviors, including soliton molecules, switching waves (platicons) and their hybrids. Tuning of the 20 GHz repetition rate by electrical actuation enables servo locking to a microwave reference, which simultaneously stabilizes the comb repetition rate, offset frequency and temporal waveform. This hybridly integrated system could be used in coherent communications or for ultra-stable microwave signal generation by two-point optical frequency division.
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