Photonic-based radar for distance and velocity measurement with multiformat waveforms.

A radar with multiformat waveforms is proposed to measure distance and velocity. A dual-polarization, dual-parallel Mach-Zehnder modulator (DP-DPMZM) is used to realize carrier-suppressed single-sideband (CS-SSB) modulation, so the switchable down-, up-, and dual-chirp signals, and the amplitude shift keying (ASK) signal, can be generated. The central frequency and bandwidth of the signals are flexible. A Mach-Zehnder modulator (MZM) is added for an optical switch to realize the generation of a pulsed signal and suppress interference in the dechirping process. A dual-drive MZM (DDMZM) is used for the dechirping process. The key component of this radar is that there are no filters used, which can significantly extend the operation bandwidth. In our test, the interference frequency caused by the CW can be suppressed. The error of the distance measurement is less than 2 cm, and the velocity error is less than 0.180 m/s. In addition, the direction of the target can be distinguished.

Microwave photonic radar for distance and velocity measurement based on optical mixing and compressive sensing.

We propose a microwave photonic compressive sensing radar for distance and velocity measurement. First, a de-chirped signal that carries distance or velocity information is extracted between the transmitted and received signals in the proposed system. Then it is mixed with a pseudo-random bit sequence in the optical domain using a Mach-Zehnder modulator. After that, the de-chirped signal can be acquired by a photodetector and an analog-to-digital converter (ADC) at a sub-Nyquist sampling rate. Finally, a reconstruction algorithm can be used to recover the de-chirped signal. In our test, the bandwidth of ADC can be shortened from 2 GHz to 500 MHz, leading to a compression factor of four. A series of frequencies from 1.043 GHz to 1.875 GHz can be compressed with a 500-MHz ADC and recovered using a reconstruction algorithm. For a moving target, the Doppler frequency shift can be calculated, and the direction of the moving target can be distinguished. The maximum relative error of distance measurement is 0.21%. The maximum relative error of velocity measurement is 2.6%. The signal-to-noise ratio can be developed from ∼15dB to ∼30dB. This microwave photonic compressive sensing radar can achieve distance and velocity measurements using few samples. Also, it provides a large bandwidth of system operation and reduces data processing and storage pressure.

Photonic generation of a dual-chirp waveform with an optoelectronic oscillator based on stimulated Brillouin scattering.

A photonic method to generate a dual-chirp microwave waveform (DCMW) is proposed and demonstrated by utilizing a stimulated Brillouin scattering based optoelectronic oscillator and a frequency scanning laser source (FSLS). There are no radio frequency sources or Mach-Zehnder modulators in the proposed structure, which makes the system simple and stable. In the experiment, an alternative scheme is utilized to replace the FSLS, and the DCMW signal with a central frequency of 4.69 GHz is generated; the bandwidth of the generated DCMW signal is up to 7 GHz and the chirp rate up to ±5.3GHz/µs. The autocorrelation and ambiguity function of the generated signal are also investigated and show good performance of pulse compression and reduction of range-Doppler coupling.

Efficient single-component white light emitting diodes enabled by lanthanide ions doped lead halide perovskites via controlling Förster energy transfer and specific defect clearance.

Currently, a major challenge for metal-halide perovskite light emitting diodes (LEDs) is to achieve stable and efficient white light emission due to halide ion segregation. Herein, we report a promising method to fabricate white perovskite LEDs using lanthanide (Ln3+) ions doped CsPbCl3 perovskite nanocrystals (PeNCs). First, K+ ions are doped into the lattice to tune the perovskite bandgap by partially substituting Cs+ ions, which are well matched to the transition energy of some Ln3+ ions from the ground state to the excited state, thereby greatly improving the Förster energy transfer efficiency from excitons to Ln3+ ions. Then, creatine phosphate (CP), a phospholipid widely found in organisms, serves as a tightly binding surface-capping multi-functional ligand which regulates the film formation and enhances the optical and electrical properties of PeNC film. Consequently, the Eu3+ doped PeNCs based-white LEDs show a peak luminance of 1678 cd m-2 and a maximum external quantum efficiency (EQE) of 5.4%, demonstrating excellent performance among existing white PeNC LEDs from a single chip. Furthermore, the method of bandgap modulation and the defect passivation were generalized to other Ln3+ ions doped perovskite LEDs and successfully obtained improved electroluminescence (EL). This work demonstrates the comprehensive and universal strategies in the realization of highly efficient and stable white LEDs via single-component Ln3+ ions doped PeNCs, which provides an optimal solution for the development of low-cost and simple white perovskite LEDs.