Autocollimators (ACs) are primarily used for two-dimension measurement with small angle. A three-dimensional AC (3D-AC) with a large measurement range and capable of 3D angle measurement is proposed based on a modified cube corner reflector (MCCR). The MCCR structure is designed by establishing the space coordinate vector relation model between AC and the reflectors with the rotation relation of Euler space. A 3D-AC angle measurement equation for MCCR dimension angle recognition is established. Experiments demonstrate that the proposed 3D-AC model can be used for 3D measurement. The measurement range of 3D-AC is 10°, and the uncertainty values for the one-dimensional and combined angle measurements are (57.10″, 55.25″, 40.43″) and (394.16″, 455.36″, 319.57″), respectively.

A photonic technique for microwave frequency measurement with flexible range and high resolution is proposed based on frequency-configurable pilot tones. The method extracts the remote unknown microwave frequency by measuring electrical power at two known pilot frequencies, avoiding dual-channel photodetection and broadband microwave power measurement over the whole interested frequency range. Moreover, it enables flexible measurement range by configuring two pilot frequencies. A proof-of-concept experiment is successfully demonstrated with the frequency range of 6-18.9 GHz and the resolution of 0.1 GHz.

An approach to measuring time delay with high speed and high precision is proposed based on using complementary frequency-swept light and frequency-shifted dechirping. The complementary frequency-swept light is generated by up-converting a linear frequency-modulated waveform into the optical domain, which sweeps linearly and fast. The frequency-shifted dechirping operation and a phase-noise-elimination algorithm are utilized to suppress the phase noise of the optical source, which enables high-precision time delay measurement without limitation of the coherence time on the measurement range. In the experiment, the bandwidth of the linear frequency-modulated waveform is set to be 4 GHz. The time delay of a spool of single-mode fiber with a length of 1 km is measured by using two different laser sources with linewidths of 1.9 MHz and 27 kHz. The standard deviations of the measured time delay are 0.42 ps and 0.52 ps, respectively, indicating that the optical phase noise has a negligible impact on the measurement results. Allan deviation is used to calculate the relative measurement errors, which are 1 × 10 ⁻⁷ and 4 × 10 ⁻⁹ within a measurement duration of 30 μs and 4.53 ms, respectively. Besides, the time delay change of an optical tunable delay line with a tuning step of 4 ps is clearly distinguished. Hence, this scheme can achieve ultrafast and high-precision time delay measurement within a large range.

An electrical probing test method is proposed based on serial or parallel modulation mixing scheme for characterizing wideband optical transceiving devices including high-speed semiconductor laser diodes, electro-absorption modulators, photodetectors, and Mach-Zehnder modulators. The method enables self-referenced frequency responses measurement, such as modulation index of semiconductor laser diodes, modulation index of electro-absorption modulators, responsivity of photodetectors, and modulation index and half-wave voltage of dual-parallel Mach-Zehnder modulators, dual-drive Mach-Zehnder modulators, and push-pull Mach-Zehnder modulators. In the demonstration, the experimental results are compared to those obtained with the conventional optical or electrical methods for accuracy. The full-electrical test nature is promising for microwave characterization of wafer level devices and circuits with fully integrated transceiving components on chip.

An electrical method is proposed for the microwave characterization of dual-drive Mach–Zehnder modulators based on heterodyne mixing. The proposed method utilizes the heterodyne products between the two-tone modulated optical sidebands and frequency-shifted optical carrier, and achieves calibration-free and bias-drift-free microwave measurement of dual-drive Mach–Zehnder modulators with high resolution electrical-domain techniques. Our method avoids the extra calibration for the photodetector and reduces half the bandwidth requirement for the photodetector and the electrical spectrum analyzer through carefully choosing a half frequency relationship of the two-tone modulation. Moreover, our measurement avoids the bias drifting problem due to the insensitivity to the bias phase of the modulator under test. The frequency-dependent modulation depths and half-wave voltages are measured for a commercial dual-drive Mach–Zehnder modulator with our method, which agree well with the results obtained by the conventional optical spectrum analysis method.

An electro-optical heterodyne scheme is proposed and demonstrated for magnitude- and phase-frequency response measurement of optical filters based on harmonics heterodyne and Wiener-Lee transformation. The method consists of an acousto-optic frequency shifter and a phase modulator located in a frequency-shifted heterodyne interferometer (FHI). The minimum phase-frequency response is simultaneously extracted from the measured magnitude-frequency response with the help of Kramers-Kronig relations and Wiener-Lee transformation. As compared with the single-sideband-based or double-sideband-based methods, our method eliminates small-signal assumption and features the immunity to the undesired spurious sidebands, enabling harmonic sideband sweeping with even-folded measuring frequency range. Prior to the conventional frequency-shifted heterodyne methods, the method enables simultaneous extraction of intrinsic magnitude and phase frequency responses for most optical filters by introducing the Wiener-Lee transformation. A phase-shifted fiber Bragg grating (FBG) is measured for extracting the frequency responses in the proof-of-concept experiment with the frequency resolution up to 50 kHz and frequency range of 80 GHz by using a frequency-swept modulation of 20 GHz.