Photonic true-time delay (TTD) beamforming has been considered as a promising technique for future wide-band phased array antenna systems. A TTD beamforming system based on a linear chirped fiber grating (LCFG) requires a tunable multi-wavelength laser source, in which the wavelengths are tuned simultaneously with equally increased or decreased wavelength spacing. We present a novel approach of a TTD laser source employing a DQPSK modulator and a highly nonlinear fiber (HNLF). The wavelength tuning is achieved by tuning the frequency of the radio frequency signal generator that drives the DQPSK modulator. Up to 41 lasing wavelengths with 0.08 nm spacing, 29 lasing wavelengths with 0.06 nm spacing and 31 lasing wavelengths with 0.12 nm spacing in 3 dB bandwidth were obtained. In theory, the multi-wavelengths can be simultaneously tuned from 10 MHz to 20 GHz in our experiments based on the fact that the frequency range of the RF signal source is from 10 MHz to 20 GHz and the bandwidth of DQPSK modulator is up to 22 GHz. The tuning precision of the RF signal generator is up to 1Hz and phase noise is about -104dBc/Hz. Therefore, the wavelengths can be tuned precisely and stably.
We proposed and demonstrated a linearly frequency-swept multi-wavelength laser source for optical coherence tomography (OCT) eliminating the need of wavenumber space resampling in the postprocessing progress. The source consists of a multi-wavelength fiber laser source (MFS) and an optical sweeping loop. In this novel laser source, an equally spaced multi-wavelength laser is swept simultaneously by a certain step each time in the frequency domain in the optical sweeping loop. The sweeping step is determined by radio frequency (RF) signal which can be precisely controlled. Thus the sweeping behavior strictly maintains a linear relationship between time and frequency. We experimentally achieved linear time-frequency sweeping at a sweeping rate of 400 kHz with our laser source.
Proc. SPIE. 9747, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications IX
KEYWORDS: Data conversion, Fiber Bragg gratings, Demodulation, Optical data conversion, Time division multiplexing, Sensing systems, Intelligent sensors, Multiplexing, Sensors, Frequency conversion, Data centers, Laser sources, Signal detection, Optoelectronics
In this paper, we propose an all-optical real-time data format conversion system to realize the efficient-utilization of the spectrum resource in the FBG sensing network. In the data format conversion unit, frequency domain sensing signals reflected by FBGs are converted into optical time division multiplexing signals with a specified wavelength in real time. Format converted data from each node are sent back to the control center for demodulation. Experimentally, data format conversion and demodulation of one sensing node is carried out with different temperature and static strain. The spectra of sensing pulses before and after data format conversion indicates that the data format conversion is successful and the spectrum resource in this node is released.
In this paper, wavelengths parallel swept technique is proposed by using an optical swept loop outside the laser cavity. A frequency shifter controlled by RF signal in the loop shifts the frequencies of the incident optical signals simultaneously with a constant value in every circulation. Experimentally, the outputs of two distributed feed back (DFB) lasers were parallel swept by using the optical swept loop. The swept step is tunable from 300MHz(24pm) to 15GHz(0.12nm) depending on the electro-optical bandwidth of the frequency shifter used in our experiments. Dual-wavelength swept output at 214 kHz swept rate with 0.08nm swept step and 122 kHz swept rate with 0.04nm swept step were achieved respectively. The swept span of the swept source was 1.6nm with a flatness of ±1.5dB.