Optical wavelength measurement is imperative in a wide range of applications, such as optical metrology, sensing, wireless communication, and so on. In this paper, we propose and demonstrate a novel microwave photonic optical wavelength measurement method based on swept wavelength-to-time mapping, where the optical wavelength is mapped to the time domain information of a microwave photonic link with the help of a swept signal. Wavelength of the optical signal under test can therefore be measured by simply measuring the time domain information. To achieve swept wavelength-to-time mapping, a bi-directional frequency-swept optical signal for reference is first constructed. The reference optical signal and the optical signal under test is then combined and launched into a photodetector for optical-to-electrical conversion. A pair of microwave pulses can be observed, which is obtained by filtering the recovered photocurrent using an electrical bandpass filter with narrow passband. The occurrence time of the filtered pulses are related to the optical wavelength under test due to the bi-directional frequency-scanning property of the reference optical signal, thus swept wavelength-to-time mapping is enabled. Only a low-speed oscilloscope is needed for optical wavelength measurement by monitoring the time-domain information of the microwave pulses in the proposed method, which provides a cost-effective approach for microwave photonic optical wavelength measurement.
Microwave photonic signal processing such as microwave frequency measurement and temperature sensing has been widely studied due to its advantages such as large instantaneous bandwidth, high resolution, flexible reconfigurability as well as immunity to electromagnetic interference. In this paper, we review our recent works about microwave photonic signal processing based on parameter-to-time mapping, where the parameters under test, such as the frequency or temperature, are mapped to the time interval of the output pulses. Parameter-to-time mapping relationship is therefore established, and the parameter can be measured by using a low-speed time-domain acquisition equipment. The microwave photonic signal processing schemes based on parameter-to-time mapping feature low-cost and high resolution, which have great potential in applications such as radar, electronic warfare and metrology systems.
With the development of the economy and the society, spectrum resources of higher frequencies are becoming increasingly scarce. Beneficial from the photonic technology, optoelectronic oscillators (OEOs) have the advantages in generating microwave signal with high center frequency and low phase noise. However, applications of OEO systems are limited by its bulky size. In this work, a hybrid integrated OEO is proposed and experimentally demonstrated. A high integration level is achieved by assembling all the optical and electrical chips. A compact fiber ring and a YIG filter are also well packaged. At the oscillation frequency of 10 GHz, phase noise of the proposed OEO is -115.83 dBc/Hz@10 kHz. Wideband frequency tuning from 3 GHz to 18 GHz is also realized, the phase noise is better than -110 dBc/Hz @10 kHz at the entire tuning range. This work shows the great potential of integrated OEO in a wide range of applications such as wireless communications and satellite communications.
The dispersive wavelength to time mapping with the entangled photon source is an effective way of measuring the spectral information of the entangled photon pairs. This approach avoids the usage of spectral filtering equipment like the monochromator, which reduces the measuring time and the system’s complexity. The wavelength-to-time mapping method can be divided into local mapping and nonlocal mapping depending on whether the measurement utilizes the frequency correlation of the entangled photon pairs. For local mapping, the spectral information of signal photons is directly mapped to the time domain through dispersion without utilizing the frequency correlation between the photon pair. For nonlocal mapping, the signal photons with spectral information are directly detected. And the corresponding idler photons are dispersed. With the help of the frequency correlation between the photon pair, the spectral information on signal photons can be recorded in count measurement. In this letter, the two types of mapping results are theoretically and experimentally compared. The theoretical result indicates that the two types of mapping results are the same when the pump light of the entangled source is ideal monochromatic with infinite linewidth. However, when using a real pump light with finite linewidth, the theoretical and experimental result of the two types of mapping is different. The difference in the result indicates the potential influence of the mapping method, which can further help to select a more suitable mapping method for different measuring conditions.
An optoelectronic oscillator (OEO) is a microwave photonic system that produces microwave signals with ultralow phase noise using a high-quality-factor optical energy storage element. This type of oscillator is desired in various practical applications, such as communication links, signal processing, radar, metrology, radio astronomy, and reference clock distribution. Recently, new mode control and selection methods based on Fourier domain mode-locking and parity-time symmetry have been proposed and experimentally demonstrated in OEOs, which overcomes the long-existing mode building time and mode selection problems in a traditional OEO. Due to these mode control and selection methods, continuously chirped microwave waveforms can be generated directly from the OEO cavity and single-mode operation can be achieved without the need of ultranarrowband filters, which are not possible in a traditional OEO. Integrated OEOs with a compact size and low power consumption have also been demonstrated, which are key steps toward a new generation of compact and versatile OEOs for demanding applications. We review recent progress in the field of OEOs, with particular attention to new mode control and selection methods, as well as chip-scale integration of OEOs.
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