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Innovative Silicon and InP Integrated Photonic Devices for RF Frequency Downconversion

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Technical Report,14 Dec 2017,14 Dec 2018

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Universiteit Gent Vzw Gent Belgium

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We demonstrated that two monolithically integrated InP-based lasers integrated on a single chip can be locked to the same optical cavity using the PDH frequency locking technique. The PDH is implemented with a single control loop and voltage control electro-optic tuning therefore avoiding significant heat dissipation. The frequency difference of the stabilized lasers can be discretely tuned at multiples of the FSR of the external optical cavity and used for RF signal generation. We presented generated tones at 12.436 GHz, 24.8735 GHz and 40.4194 GHz, limited only by the bandwidth of the photodetector, with FWHM 40 kHz. The SSB phase noise is lower than 50 dBcHz for all frequency offsets. The obtained SSB phase noise of the RF signal is not as good as state of the art oscillators up to several tens of GHz frequency at the moment. The phase noise can be improved however in two ways. At low offset frequencies couple of MHz further suppression of the laser frequency noise can be achieved with improvement of the PDH locking system with higher gain. At high offset frequencies, lasers with lower intrinsic linewidth should be used since implementation of PDH locking with such control bandwidths is very challenging. Despite the SSB phase noise not being better than the state-of-the-art this technique has several advantages. The tuning range can be extended by more than an order of magnitude by using lasers realised in the same technology. Such tuneable lasers can be tuned over tens of nm several THz and can be stabilized in the same way as shown in this report. Therefore discrete tuning from microwave to THz frequencies can be enabled. In the same technology we have demonstrated that widely tuneable lasers can have roughly the same frequency noise level independent of their lasing wavelength. The implementation of this technique with such lasers would yield virtually

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