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Flattening laser frequency comb spectra with a high dynamic range, broadband spectral shaper on-a-chip

Jovanovic, Nemanja and Gatkine, Pradip and Shen, Boqiang and Gao, Maodong and Cvetojevic, Nick and Ławniczuk, Katarzyna and Broeke, Ronald and Beichman, Charles and Leifer, Stephanie and Jewell, Jeffery and Vasisht, Gautam and Mawet, Dimitri (2022) Flattening laser frequency comb spectra with a high dynamic range, broadband spectral shaper on-a-chip. Optics Express, 30 (20). p. 36745. ISSN 1094-4087. doi:10.1364/oe.470143.

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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 smooth spectrum light source (superluminescent diode), we reduced the static spectral variation to ∼3 dB, limited by the properties of the components used in the circuit. On a laser frequency comb which had strong spectral modulations, and some at high spatial frequencies, we nevertheless managed to reduce the modulation to ∼5 dBs, sufficient for astronomical applications. The size of the device is of the order of a US quarter, significantly cheaper than their bulk optic counter parts and will be beneficial to any area of science that requires spectral shaping over a broad range, with high dynamic range, including exoplanet detection.

Item Type:Article
Related URLs:
URLURL TypeDescription
Jovanovic, Nemanja0000-0001-5213-6207
Gatkine, Pradip0000-0002-1955-2230
Shen, Boqiang0000-0003-0697-508X
Gao, Maodong0000-0002-7791-0008
Cvetojevic, Nick0000-0002-7465-4176
Beichman, Charles0000-0002-5627-5471
Leifer, Stephanie0000-0002-8980-7825
Vasisht, Gautam0000-0002-1871-6264
Mawet, Dimitri0000-0002-8895-4735
Additional Information:Keck Institute for Space Studies; European Research Council (grant agreement CoG - 683029); National Aeronautics and Space Administration (80NM0018D0004, HST-HF2-51478.001-A, NAS5-26555); David and Ellen Lee Postdoctoral Fellowship at the California Institute of Technology. This work was produced with support from the Keck Institute for Space Studies. N. Cvetojevic acknowledges the funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement CoG - 683029). P. Gatkine is supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51478.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Gatkine also acknowledges the support from David and Ellen Lee Postdoctoral Fellowship at the California Institute of Technology. Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).
Group:Astronomy Department, Infrared Processing and Analysis Center (IPAC), Keck Institute for Space Studies
Funding AgencyGrant Number
Keck Institute for Space Studies (KISS)UNSPECIFIED
European Research Council (ERC)683029
NASA Hubble FellowshipHST-HF2-51478.001-A
David and Lucile Packard FoundationUNSPECIFIED
Issue or Number:20
Record Number:CaltechAUTHORS:20221031-575177800.13
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117654
Deposited By: Research Services Depository
Deposited On:09 Nov 2022 18:14
Last Modified:11 Nov 2022 17:43

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