We propose a novel Polarization-Dependent Loss (PDL) measurement method to achieve optical device polarization characterization. The method utilizes high-fineness frequency sweeping based on Microwave Photonics (MWP) to achieve high frequency resolution. Theoretically, a sub-Hz frequency resolution is available. In the experiment, the stimulated Brillouin scattering (SBS) in a 5-km single-mode fiber serves as the device under test (DUT). The PDL is measured with a frequency resolution as high as 100 kHz over a frequency span of 400 MHz, demonstrating the advantages of high frequency resolution.
Photodetectors (PDs) are optoelectronic (O/E) devices to achieve optical-to-electrical conversion, which are essential and of great importance in optical communication, optoelectronic oscillator, etc. Measuring O/E frequency responses, including magnitude response and phase response, is a fundamental measurement processing in their development and application. Microwave photonics (MWP) is a promising solution to achieve ultrahigh-resolution characterization. However, the frequency measurement range is restricted by the relatively small working bandwidth of modulators. To enlarge the measurement range, an approach to measure magnitude response of O/E devices is proposed and experimentally presented. In the approach, two optical double-sideband (ODSB) signals with the carrier suppression are generated. One ODSB signal filtered out +1st-order sideband is used as the frequency-shifted carrier. By coupling the frequency-shifted carrier and the other ODSB signal, an asymmetrical ODSB signal is thus achieved and served as a probe signal. After square-law detection of a PD under test, a photocurrent is produced. Detecting the frequency downconversion component in the produced photocurrent, the magnitude response in the low-frequency regime is obtained. Similarly, the magnitude response in the high-frequency regime is observed via extracting the magnitude information of the frequency up-conversion component. Thanks to the MWP-based frequency conversion, the measurement range is doubled, and the nonlinear error is suppressed. Furthermore, an ultrahigh-frequency resolution up to Hz or even sub-Hz is theoretically achievable. In an experiment, a 20-GHz commercial PD is accurately measured using a 200-kHz resolution. A measurement range as large as 67 GHz is enabled by 33.5 GHz RF frequency sweeping.
Optoelectronic devices, such as photodetectors (PDs), integrated coherent receivers (ICRs) and microwave photonics integrated circuits (MPICs), are the fundamental and essential components to bridge the optical world and the electronic world and massively applied in emerging fields. Optoelectronic frequency responses, representing the optical-to-electrical conversion efficiency at different frequencies, are the primary and critical parameters for optoelectronic devices, which are essential and of great importance to be precisely measured in their development, manufacture and application. To achieve ultrahigh-resolution and multi-dimensional characterization, optoelectronic vector analyzers (OEVAs) utilizing photonics-based frequency conversion have been proposed and demonstrated. Benefitting from photonics-based frequency conversion and ultrahigh-resolution microwave technologies, the ultrahigh-resolution and broadband optoelectronic frequency responses are de-coupled from the joint frequency responses. Theoretically, sub-Hz frequency resolution together with hundred-GHz measurement range is potentially achievable. However, limited by the high-order sidebands and the high-order intermodulation sidebands stimulated by the nonlinear electro-optic conversion, the measurement accuracy is deteriorated and the dynamic range is considerably limited. Additionally, for the on-chip measurement, the relatively narrow working bandwidth of the on-chip electro-optic modulators places a restriction on the measurement range. Recently, great efforts have been devoted to eliminate the nonlinear errors, improve the dynamic range and extend the measurement range. In this paper, the influence of the high-order sidebands and high-order intermodulation sidebands on the measurement accuracy and the dynamic range of the proposed OEVA are comprehensively investigated. The techniques for implementing high-accurate and broadband OEVAs are reviewed and discussed.
Most of the efforts devoted to the area of optical communications were on the improvement of the optical spectral
efficiency. Varies innovative optical devices are thus developed to finely manipulate the optical spectrum. Knowing the
spectral responses of these devices, including the magnitude, phase and polarization responses, is of great importance for
their fabrication and application. To achieve high-resolution characterization, optical vector analyzers (OVAs) based on
optical single-sideband (OSSB) modulation have been proposed and developed. Benefiting from the mature and highresolution
microwave technologies, the OSSB-based OVA can potentially achieve a resolution of sub-Hz. However, the
accuracy is restricted by the measurement errors induced by the unwanted first-order sideband and the high-order
sidebands in the OSSB signal, since electrical-to-optical conversion and optical-to-electrical conversion are essentially
required to achieve high-resolution frequency sweeping and extract the magnitude and phase information in the electrical
domain. Recently, great efforts have been devoted to improve the accuracy of the OSSB-based OVA. In this paper, the
influence of the unwanted-sideband induced measurement errors and techniques for implementing high-accurate OSSB-based
OVAs are discussed.
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