All-optical microwave waveform transformation based on photonic temporal processors.

An all-photonic approach of microwave waveforms generation and transformation is proposed and experimentally demonstrated. From the perspective of envelope function operation in time domain, an initial triangular waveform is transformed into square waveform and sawtooth (or reversed-sawtooth) waveform via two types of differentiators, respectively. In addition, by using a SOA as a multiplier, both bright and dark parabolic pulses are achieved, which are further transformed into sawtooth (or reversed-sawtooth) waveform by taking the first derivative operation. The feasibility of the system is verified by theoretical analysis and simulation. In experiment, all of the expected results are successfully demonstrated and agree with the theoretical analysis well. This scheme provides a novel access to implement all-optical microwave waveforms generation, transformation, signal processing and computing.

Tunable microwave sawtooth waveform generation based on one single-drive Mach-Zehnder modulator.

A photonic method of sawtooth waveform generation by using one single-drive Mach-Zehnder modulator is proposed and experimentally demonstrated. Depending on the polarization-sensitive characteristic of the modulator, the modulation sidebands and optical carrier can independently exist on two orthogonal polarization directions. Therefore, the required Fourier components can be manipulated on two polarization dimensions separately, and the superposition of the orthogonal optical envelopes synthesize a sawtooth waveform in time domain. The feasibility of the scheme is theoretically analyzed. In the experiment, sawtooth waveforms with full duty cycle at 3, 5, and 8 GHz are obtained, which agree with the simulation results well.

Tunable single-mode microwave signal generation utilizing an all-optical coupled microwave oscillator.

A tunable all-optical coupled microwave oscillator is proposed and experimentally demonstrated. This system has no any electrical microwave devices as well as photoelectric conversion and electro-optic modulation. In this scheme, a fiber ring laser not only provides a set of frequency references but also acts as an active optical resonator. The oscillation frequency selection is carried out by cavity modes transfer and injection locking process. Due to the mode pulling effect, a self-adapting oscillation frequency locking is achieved. Through the microwave envelope detection and feedback modulation in a semiconductor optical amplifier (SOA), a microwave signal can be generated by a pure optical oscillation. In the experiment, good quality and high stability single-mode microwave signals are obtained, whose frequencies can be tuned from 6.93 GHz to 25.54 GHz by simply adjusting the wavelength of the master laser. Under different operation frequencies, the measured single-sideband phase noises are approximately -95 dBc/Hz at a 10-kHz offset from the carriers.

Photonic microwave waveforms generation based on two cascaded single-drive Mach-Zehnder modulators.

A new photonic scheme for various waveforms generation has been proposed and demonstrated. In the scheme, two cascaded single-drive LiNbO3 Mach-Zehnder modulators serve as pulse shaper and the polarization-dependent character of the modulators is fully exploited and utilized. By arranging the polarization states of the incident light, two different spectra are achieved on two orthogonal polarization components respectively. Finally, the desired waveforms can be obtained by superimposing the photocurrents of the two orthogonal signals on a photodetector. The detailed theoretical analyses and simulations are given. In the experiment, square-shaped waveform, triangular waveform and sawtooth (or reversed-sawtooth) waveform are obtained successfully. Furthermore, an approach to smoothing the sawtooth waveform with fewer harmonics is suggested and verified.

All-optical microwave oscillator based on semiconductor optical amplifier and stimulated Brillouin scattering.

An all-optical microwave oscillator is proposed and experimentally demonstrated. Based on a pure photonic feedback loop, this system can generate a photonic microwave signal without optical-electrical-optical conversion or any electrical microwave devices. A semiconductor optical amplifier implements the functions of microwave envelope detection and feedback modulation. Meanwhile, Brillouin-selective sideband amplification is employed to lock oscillation frequency. In experiment, a good quality microwave signal with a frequency of 10.8 GHz is obtained. The tunability is also demonstrated by adjusting the Brillouin pump wavelength.

Photonic microwave waveforms generation based on time-domain processing.

A new photonic approach of microwave waveform generator based on time-domain synthesis is proposed and experimentally demonstrated, in which two single-drive Mach-Zehnder modulators biased at quadrature point are severed as optical pulse carvers and various microwave waveforms can be generated by carving and overlapping optical field envelopes. The theoretical analysis and simulation are developed. In experiment, a square waveform with 50% duty cycle, triangular waveform with full duty cycle, and sawtooth (or reversed-sawtooth) waveform with 50% duty cycle are generated. Furthermore, a frequency doubling sawtooth (or reversed-sawtooth) waveform with full duty cycle is also obtained.