Ka-band thin film lithium niobate photonic integrated optoelectronic oscillator

Rui Ma; Zijun Huang; Shengqian Gao; Jingyi Wang; Xichen Wang; Xian Zhang; Peng Hao; X. Steve Yao; Xinlun Cai

doi:10.1364/PRJ.521301

Photonics Research, Volume. 12, Issue 6, 1283(2024)

Ka-band thin film lithium niobate photonic integrated optoelectronic oscillator Editors' Pick

Rui Ma¹, Zijun Huang¹, Shengqian Gao¹, Jingyi Wang¹, Xichen Wang², Xian Zhang¹, Peng Hao^2,4、*, X. Steve Yao^2,3,5、*, and Xinlun Cai^1,6、*

Author Affiliations

¹State Key Laboratory of Optoelectronic Materials and Technologies, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China

²Photonics Information Innovation Center and Hebei Provincial Center for Optical Sensing, College of Physics Science and Technology, Hebei University, Baoding 071002, China

³NuVison Photonics, Inc., Las Vegas, Nevada 89109, USA

⁴e-mail: haopeng@hbu.edu.cn

⁵e-mail: syao@ieee.org

⁶e-mail: caixlun5@mail.sysu.edu.cn

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Figures & Tables(7)

Fig. 1. Schematics of two different OEOs utilizing different TFLN PICs. (a) Fixed frequency OEO realized with a TFLN PIC containing an MZM and an add-drop MRR (left) with its operation principle (right). (b) Frequency-tunable OEO realized with another TFLN PIC containing a PM and a notch MRR (left) with its operation principle (right).

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Fig. 2. (a) The microscope image of the TFLN PIC containing an MZM and an add-drop MRR for realizing the fixed-frequency OEO. (b) The microscope image of another TFLN PIC consisting of a PM and a notch MRR for realizing the ultra-wide range frequency-tunable OEO. (c) The scanning electron microscope (SEM) image of the etched LNOI waveguide and its sidewalls (left) and the capacitance-loaded traveling-wave electrodes (CL-TWEs) (right). (d) The SEM image of the zoom-in view of the coupling region of MRR.

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Fig. 3. Experimental results of the fixed-frequency Ka-band OEO. (a) The measured EO bandwidth (S21 parameter) of the MZM with a total modulation length of 2.5 cm. Inset: The transmission spectrum of the MZM vs. bias voltage (Vb), indicating an ER of 29 dB. (b) The measured normalized optical transmission spectrum of the MZM as a function of the applied DC voltage, showing a Vπ of 1.2 V. (c) The measured transmission spectrum of the add-drop MRR. Inset: A zoom-in view of the transmission spectrum of one of the drop ports showing the 3 dB bandwidth, ER, and Q value of the add-drop MRR. (d) The measured frequency response of the OEO’s SSOL gain consisting of the laser, the MZM, the add-drop MRR, the EDFA with a nominal gain of 2 dB, the PD, the LNA with a power gain of 8 dB, and the EC.

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Fig. 4. (a) The photograph of the experimental setup for measuring the phase noise of the OEO. (b) The zoom-in view of the chip test bench. (c) Comparison of the phase noise between the fixed-frequency OEO (blue curve) and a commercial microwave source (Keysight: E8257D) (red curve). (d) The RF spectrum of the 30 GHz signal measured by an RFSA with a frequency span of 40 MHz and a resolution bandwidth (RBW) of 40 kHz. Inset: The zoom-in RF spectrum measured with a frequency span of 1 MHz and an RBW of 900 Hz.

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Fig. 5. Experimental results of the TFLN chip and the resulting frequency-tunable OEO. (a) The measured transmission spectrum of the notch MRR. Inset: A zoom-in view of the transmission spectrum of one of the resonances showing the 3 dB bandwidth, ER, and Q value of the notch MRR. (b) The wavelength shift of a resonance of the notch MRR as a function of the applied DC voltage. (c) The frequency response of the SSOL gain of the OEO with an LNA power gain of 29 dB with an optical power of 9 dBm into the PD. (d) Experimental results showing the wide range frequency tunability of the OEO. (e) The RF spectrum of the 30 GHz signal generated by the OEO measured with an RFSA with a frequency span of 40 MHz and a resolution bandwidth (RBW) of 40 kHz. (f) The measured phase noises of the OEO operating at 20, 30, and 35 GHz (blue, black, and green curves), as compared with a commercial microwave source (Keysight: E8257D) (red curve). (g) The measured phase noises of the generated RF signals at 10 kHz offset from different oscillation frequencies. (h) The measured optical spectrum when the OEO is operating at 30 GHz.

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Fig. 6. The experimental setup for measuring the frequency response of the SSOL gain of an OEO.

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Table 1. Comparison of Our Work with the Previous Photonic Integrated OEOs^a

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Table 1. Comparison of Our Work with the Previous Photonic Integrated OEOs^a

Material Platforms	Integrated Components	RF Frequency	Measured Phase Noise (dBc/Hz at 10 kHz)	Fiber-Free Equivalent Phase Noise (dBc/Hz at 10 kHz)
InP [35]	DML, ODL, PD	8.87 GHz	−60	−60
SOI [36]	PM, micro-disk, PD	3–7.4 GHz	−80	−80 ( $Q_{opt} \approx 1.4 \times 10^{5}$ , $L_{Q} \approx 2.4 cm$ )
SOI [38]	Hybrid-integrated (500 m)	3–18 GHz	−116	–
SOI [39]	MZI, MRR, PD (50 m)	0–20 GHz	−80	−31 ( $Q_{opt} \approx 10^{6}$ , $L_{Q} \approx 17 cm$ )
Chalcogenide [32]	Only chalcogenide waveguides (25 m)	5–40 GHz	−78	–
TFLN (this work)	MZM, micro-ring (25 m)	30 GHz	−102	−48 ( $Q_{opt} \approx 2.8 \times 10^{5}$ , $L_{Q} \approx 4.8 cm$ )
TFLN (this work)	PM, micro-ring (25 m)	20–35 GHz	−87	−46 ( $Q_{opt} \approx 1.3 \times 10^{6}$ , $L_{Q} \approx 22 cm$ )

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Rui Ma, Zijun Huang, Shengqian Gao, Jingyi Wang, Xichen Wang, Xian Zhang, Peng Hao, X. Steve Yao, Xinlun Cai, "Ka-band thin film lithium niobate photonic integrated optoelectronic oscillator," Photonics Res. 12, 1283 (2024)

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