High-speed electro-optic Phase Modulators (PMs) are critical devices in microwave photonics and optical communication. Optical spectrum analysis is widely used to measure the modulation depth of PMs thanks to simple structure and wide measurement frequency range. To further obtain the accurate frequency response especially the half-wave voltage of PMs, the microwave driving power input to the electrical port of PMs must be measured accurately. However, the source adapter network such as coaxial cables and connectors for connecting the microwave source and the PM under test will result in degraded response, which should be de-embedded. In this study, an improved optical spectrum analysis method is proposed to measure the frequency response of PMs based on microwave fixture de-embedding. In the proposed scheme, the microwave power transmitted from the microwave source to the PM is investigated by using signal flow graph to track the accurate driving power input to the PM, including transmission attenuation and impedance mismatch of the source adapter network and the PM. The accurate frequency response including modulation depth, half-wave voltage and relative response of the PM are obtained. In a proof-of-concept experiment, a commercial PM has been accurately measured in the frequency range of 1–30 GHz to demonstrate the feasibility of the proposed method. Our method fully calibrates the microwave power loss and the port impedance mismatch, which is applicable for those PMs even without good impedance match. Moreover, our method features simple structure and broadband measurement thanks to the optical spectrum analysis scheme.
An improved self-reference photonic sampling method is proposed to measure the frequency response of photodiode (PD) chips. In the proposed scheme, the uneven response of the Mode-Locked Laser Source (MLLS) is eliminated by using the half-frequency photonic sampling measurements. The microwave de-embedding under short-open-load-device termination is used to realize on-chip de-embedding of the adapter network connected to the receiver of the microwave network analyzer in terms of the transmission loss and the impedance mismatch. The proposed on-chip measurement method is free of any extra electro-optical transducer standard, and an accurate measurement can still be realized without an impedance match.
A simple and novel method is proposed for the self-calibrated measurement of high-speed photodetectors (PDs) based on photonic sampling by using a mode-locked laser (MLL). Through the photonic sampling measurements, the uneven response of the MLL can be determined. The prominent advantage of the proposed method lies that the self-reference extraction of the frequency response of the PD can be achieve without the need of any extra electrical/optical transducer standard. In the experiment, a commercial PD is measured by using a MLL with the repetition frequency of 21.936 MHz. The measurement results fit in with the conventional electro-optic frequency sweep measurement.
Electroabsorption-modulated laser (EML) is integrated by distributed feedback (DFB) laser and electro-absorption modulator (EAM). Microwave interaction in the EML has been observed to limit modulation performance especially in high frequency region. In this work, the EML is investigated as a three-port network with two electrical inputs and one optical output. Scattering matrix of the device was derived theoretically and obtained experimentally. Thus, microwave equivalent circuit model of the EML can be established and microwave interaction between the DFB laser and the EAM was successfully extracted. The results reveal that microwave interaction within an integrated EML contains both electrical isolation and optical coupling. The electrical isolation is bidirectional while the optical coupling is directional, which aggravates the performance of the EML. This result can provide a reference for further device optimization design.
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