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.
An approach to measuring high-frequency responses of electro-absorption modulated lasers (EMLs) is proposed based on fixed low-frequency pilot analysis. The fixed low-frequency pilot is inserted into the microwave driving signal loaded on the EML through amplitude modulation. Then, the high-frequency response of EML can be obtained by extracting and analyzing the pilot (kHz level) after photodetection, thereby realizing the low-frequency detection for EML measurement. Moreover, the method is independent of the responsivity fluctuation of the photodetector due to the fixed frequency analysis and enables the self-calibrated frequency response measurement of high-speed EML.
A slowly-varying-envelope photonic sampling method is proposed for hyperfine and ultra-wideband frequency response measurement of high-speed photodetectors (PDs). The measuring frequency range of PD is firstly divided into several segments by the repetition frequency fr of a mode-locked laser diode (MLLD), and the hyperfine frequency response measurement of the PD in every segment is then achieved by applying a slowly-varying-envelope microwave modulation sweeping up to fr/2, which is also independent of the uneven responses of the MLLD and the Mach-Zehnder modulator (MZM). Finally, through carefully choosing the joint-frequency of photonic sampling, the ultra-wideband frequency response of the PD can be obtained with the help of seamlessly stitching different segments. Most importantly, the frequency response of the PD at any frequency can be measured by subtly changing the frequency of photonic sampling from DC to fr/2. Moreover, the measuring frequency range of the PD can be extended by 2(n+1)-fold relative to the modulation frequency range of the MZM, where the microwave frequency swept up to fr/2 enables the measuring frequency range up to (n+1)fr.
An approach to measuring ultra-wideband frequency responses of high-speed photodetectors (PDs) is proposed based on low-speed photonic sampling. The optical frequency comb lines of a mode-locked laser diode (MLLD) can be used as the ultra-wideband and scalable optical stimulus of PD. The relative frequency response of PD can be extracted by analyzing the frequency components at comb lines of the MLLD. Thereinto, the uneven response of the MLLD can be eliminated through the specific frequency photonic sampling, thereby realizing the self-referenced and ultra-wideband measurement of PD. Moreover, the measuring frequency range is 2M-fold expanded with respect to the operating range of the microwave modulation frequency.
A self-calibrated method is proposed for electrical spectrum measurement of optical frequency comb (OFC) based on segmental electro-optic up-conversion. In the method, every N comb teeth of OFC are divided into one segment in the frequency domain, and M segments are investigated with the measuring frequency range of M×N×fr (fr is the repetition frequency of the OFC). Through symmetric frequency modulation, intra-segment measurement and seamless stitching between different segments are performed. Finally, only a low-frequency microwave source is required to achieve the electrical spectrum measurement of OFC within ultra-wideband frequency range, and the measuring frequency range can be 2M-fold expanded with respect to the modulation frequency rang. Meanwhile, the frequency responses of MachZehnder modulator and photodetector are fully cancelled out, realizing the self-calibrated electrical spectrum measurement of OFC within ultra-wideband frequency range.
An electrical method is proposed for the absolute time-delay characterization of optical delay components based on the frequency-shifted self-heterodyning. The method utilizes the electrical spectrum of the heterodyne products between the delayed optical signal and the frequency-shifted optical carrier, and achieves the intrinsic absolute time-delay measurement from the notch frequencies of the spectrum at microwave region. Moreover, our method enables highresolution and wide range measurement with low-frequency electrical spectrum analysis. The theoretical analysis is supported by experimental results.
A two-tone spectrum analysis method is proposed for self-referenced microwave characterization of high-speed electro-optic phase modulators (PMs) based on the frequency-shifted heterodyning. The method avoids correcting the roll-off responsivity of photodetection and alleviates the bandwidth requirements of the high-speed photodetector and the electrical spectrum analyzer. Moreover, it achieves very high frequency resolution and high stability measurement by the use of the two-tone frequency-shifted heterodyning.
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