A tunable all-optical microwave generator based on period-one (P1) dynamics of an external optically injected distributed-feedback laser diode (DFB-LD) is proposed and demonstrated. A DFB-LD implements the functions of light source, microwave frequency selection, and optical–optical modulation. To overcome the frequency drift in P1 oscillation process, a set of reference frequencies from a fiber ring laser (FRL) is introduced. Once the P1 oscillation signal and the modes of FRL are coupled, the whole system is closed and a stable frequency determined by P1 oscillation can be established. In the experimental verification, tunable photonic microwave signals with frequencies from 6.42 to 21.36 GHz are obtained. The measured single-sideband phase noise is −83 dBc / Hz at 10-kHz offset, which is operation frequency independent.
KEYWORDS: Fiber lasers, Sensors, Demodulation, Head, Signal to noise ratio, Sensing systems, Laser systems engineering, Temperature metrology, Optical filters, Polarization
In this paper, a customizable, sensitive fiber laser temperature-sensing scheme based on beat frequency demodulation method is proposed. The scheme adopts a ring fiber laser cavity structure and monitors temperature variations by tracking changes in the beat frequency signal (BFS). An erbium-doped fiber amplifier is used to provide gain for the optical fiber laser sensing system, and an ordinary single-mode fiber is used as the sensing head. Sensing fibers of different lengths were heated, and the sensitivities were estimated at -0.177, -0.538, and -1.116 kHz/°C for lengths of 1, 4, and 8 m, respectively. Meanwhile, by measuring the monitored frequency shifts, different sensitivities were obtained, estimated at -0.42 and -1.12 kHz/°C for monitored frequencies of 0.5 and 1.168 GHz, respectively. The BFS bandwidth reaches to 8.0 GHz, the signal-to-noise ratio is approximately 65 dB, and the -3dB linewidth is less than 2.5 kHz.
A simple scheme of tunable parabolic pulses generation is proposed. Mathematically, a parabolic function is a quadratic function, which is equivalent to a sine-squared function when the independent variable is small enough. Since the transmissivity curve of Mach–Zehnder modulator is exactly a sine-squared function, bright parabolic pulse or dark parabolic pulse can be obtained that a linear drive signal with small voltage is used to map a center range of the peak or valley of the curve to the time domain. Starting from a sinusoidal signal, the second-order approximation triangular signal is simply obtained and used as a drive signal. By setting the bias point appropriately, parabolic pulses with the same or double frequency as the drive signals can be generated. Theoretical analysis and simulation are given. In the experiment, full-duty-cycle parabolic pulses at 2, 3, and 4 GHz and corresponding frequency-doubled pulses are obtained, which are consistent with the theoretical expectations.
An all-optical microwave oscillator is proposed and experimentally demonstrated, in which a distributed feedback laser diode (DFB-LD) acts as light source and optical-optical modulator simultaneously. By employing stimulated Brillouin scattering (SBS) process for oscillation frequency selection and active optical comb filter for side-modes suppression, single-mode photonic microwave signal generation can be achieved through a pure optical oscillation. In the experiment, a stable 10.87-GHz photonic microwave signal is obtained. The signal quality is evaluated by measuring the side-mode suppression ratio and single side-band phase noise of the signal. The corresponding values are 42 dB and −85 dBc / Hz at 10 kHz, respectively. This scheme explores the innovative application potentiality of DFB-LD, which will benefit on-chip photonic microwave systems.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.