We review recent results on exploiting microwave photonics to enable simultaneous interrogation of multiple fiber Bragg grating (FBG)-based sensors. In particular, we describe the use of (1) microwave photonic filtering and (2) chirped microwave pulse generation and compression as a means to map the wavelength (spectral) changes in the response of FBG-based sensors (specifically, an in-fiber Fabry-Pérot cavity sensor based on FBGs, FBG sensors directly, and a linearly chirped FBG sensor) to applied temperature (or strain) to the power of a radio-frequency signal (i.e., a wavelength-to-power mapping) or to the correlation peak of the compressed microwave signal. The approaches support high-resolution and high-speed interrogation and can be suitable for large scale sensing networks.

This paper proposes a system based on the chirped optical pulse sequence (COPS)-stimulated Brillouin scattering (SBS) effect that utilizes two-dimensional information mapping to realize instantaneous, high-precision and ultra-broadband microwave frequency measurement (MFM). In the proposed MFM system, the unknown signals of different frequencies are frequency-selected by the SBS effect on the COPS to obtain time-dimensional information corresponding to the frequency. The differential response of the optical band-pass filter at different wavelengths is then used to acquire the amplitude-dimensional information corresponding to the frequency. Simultaneous mapping of these dimensions allows for high-precision measurement of the signal under test. The proposed system's single-tone, dual-tone and quad-tone microwave frequency measurements are validated experimentally, and the proposed system exhibits a minimum measurement time of 100 ns with a frequency measurement accuracy of less than 1 MHz and an instantaneous bandwidth exceeding 20 GHz.

In this paper, a novel photonic scheme for the generation of square and triangular waveforms is proposed and experimentally demonstrated by using a dual-drive Mach–Zehnder modulator (DDMZM) without any optical signal processing. By properly setting the modulation index of the DDMZM, the square and triangular microwave waveforms could be easily achieved in conjunction with a 90° hybrid coupler. Furthermore, the modulation index of the DDMZM could be tuned for a low radio frequency (RF) signal power requirement by tuning the phase difference of the RF signals applied to the two arms of the DDMZM. The proposed scheme for the photonic generation of microwave waveforms is theoretically analyzed and experimentally demonstrated. The periodical triangular and square waveforms with repetition rates of 5 GHz, 8 GHz, and 10 GHz are successfully obtained. The root-mean-square errors between the generated and theoretical triangular and square waveforms with a repetition of 5 GHz are 0.042 and 0.053, respectively.

A novel scheme for generating full-duty-cycle triangular and square pulses based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The scheme can generate a tuneable fundamental tone corresponding to the repetition rate of the pulses without any external radio frequency source. The “Vernier effect” is realised using two chirped fibre Bragg gratings, which can effectively improve the side-mode suppression ratio. The oscillation frequency is tuned from 2.5 to 6 GHz in an experiment to verify the theory, and the phase noise of the generated fundamental tone is measured to be −115 dBc/Hz at an offset frequency of 10 kHz. By appropriately setting the gain of the OEO loop, the power of the first- and third-order harmonics can be adjusted to meet the required power ratio. Periodical triangular pulses with repetition rates of 5 GHz, 6 GHz and square pulses with repetition rates of 2.5 GHz, 5 GHz were successfully generated. The root–mean–square errors are measured as 0.026 and 0.083 at a repetition rate of 5 GHz.

A novel polymer waveguide for surface plasmon resonance (SPR) sensing is theoretically proposed and experimentally demonstrated. The waveguide sensor simply consists of a polymer and a thin gold film on a silica layer. According to the multilayer transfer-matrix theory and the multiple reflection theory, a formula describing the reflectivity of total light power is deduced and analyzed, which is related to the dielectric constant of both the waveguide and the metal, the thickness of the metal film, and the length of the sensing area. By the addition of liquids with refractive indices ranging from 1.40 to 1.47 in the sensing area, the proposed polymer waveguide-based surface plasmon resonance sensor exhibited an experimental sensitivity of 1489 dB/RIU. With a refractive index range between 1.45 and 1.47 beyond the measurement range of typical SPR fiber based sensors, the reported device operates with very high sensitivity. The proposed portable, compact, and simple polymer waveguide-based surface plasmon resonance sensor shows potential for low cost and on-chip multiple channel sensing for practical applications.

We propose and experimentally demonstrate a photonics method for generating broadband frequency hopping (FH) microwave signals based on an optoelectronic conversion (OEC) loop. In the proposed scheme, FH signals are generated after feedback modulation when low-frequency seed pulses are applied to the MZM in the OEC loop. The scheme can achieve a large-scale frequency hopping between S/C/X bands and C/X/Ku frequency bands. The experimental results indicate that 3-level FH signals with frequencies of 3/6/12 and 4/8/16 GHz have been successfully generated. Frequency-hopped linear frequency modulation (FH-LFM) signals from 2.5 GHz to 4.5 GHz, 5 GHz to 9 GHz and 10 GHz to 18 GHz with different chirp rates can also be generated. The achievable time-bandwidth product (TBWP) is as high as 15400. The autocorrelation results indicate that FH-LFM has good pulse compression ability. The pulse width, period and bandwidth of the FH signal can be adjusted flexibly. The proposed system does not require any optical filters or high-frequency RF signal source. It has potential to apply in radar, electronic warfare and wireless communication systems.