Numerical simulations are used to solve the coupled partial differential equations describing stimulated Brillouin scattering (SBS) built up from random thermal phonons as a function of time and the longitudinal spatial coordinate in an optical fiber. In the case of a passive fiber, a laser beam is incident with constant power, but its frequency is linearly ramped at 1.55
We investigate the temporal and energy characteristics of gain-switched diode-pumped Er-Yb codoped fiber lasers by establishing and solving an experimentally verified numerical model. With a pulsed laser diode pumping at 975 nm and in a proper repetition rate range, the laser exhibits the potential of lasing pulses of several hundred nanoseconds with excellent synchronism at around 1 and 1.5
We demonstrate a sinusoidal-gated InGaAs/InP single photon avalanche diode (SPAD) pair with high photon detection efficiency (PDE) and low dark count rate (DCR). The photodiode pair is biased in a balanced configuration with only one of the SPADs illuminated. The advantage of balanced detectors is cancellation of the common component of the output signal, which in this case arises from sinusoidal gating. In conventional sinusoidal gating, narrow-band RF filters are used to eliminate the gating signal while imparting minimal change to the avalanche pulses. A disadvantage of this approach is that the requisite filters fix the operating frequency, whereas the balanced SPAD receiver is frequency agile. At a laser repletion rate of 1 MHz and a temperature of 240 K, the DCR and PDE are 58 kHz and 43%, respectively. The afterpulse probability is lower than a single sinusoidal-gated SPAD. Jitter of 240 ps is achieved with one photon per pulse and an excess bias of 1.6%.
Distributed sensing using all-fiber laser-based acoustic sensors has been demonstrated recently for large area sensing. However, the sensitivity of this type of sensor has so far been much lower by comparison with currently available optical microphones. This paper studies the use of controlled interaction between the modes of oscillation in a fiber laser to enhance the sensitivity of acoustic wave detection. The responses of individual longitudinal modes to acoustic waves in a dual-wavelength fiber laser are demonstrated. With the experimental setup that has been developed, observation of a single wavelength output from the dual-wavelength laser shows optical responses to acoustic waves at 23 dB below the triggering threshold of laser dynamics, when compared with the previous scheme based on uncontrolled multimode operation.
In this paper, a comprehensive experimental study of the dynamics of an actively Q-switched Yb-doped GTWave-based fiber laser is presented. It is shown that the appearance of the Q-switching regime in the laser is sensitive to both the repetition rate and the temporal width of the transparency window of an acousto-optical Q-switch modulator placed in the cavity. It is also shown that, at low repetition rates, a peculiar self-Q-switch regime induced by stimulated Brillouin scattering is observed in the laser, which interferes stochastically with the regular (true) active Q-switching mode. While increasing the Q-modulator repetition rate, the self-Q-switch pulsing steadily vanishes but the true Q-switching remains. The latter, however, becomes strongly subjected, while further increasing the Q-switch repetition rate, by the nonlinear laser dynamics effects. That is, the laser is allowed to operate at certain subharmonics of the repetition rate or in some specific regimes that occur at laser transients from one attractor to another.
Temperature controllers based on proportion-integration-differentiation (PID) control strategy are widely used in tunable semiconductor laser modules for optical communication systems. A properly designed temperature controller (consisting of a thermoelectric cooler, a thermistor, and control circuits) can maintain a nearly constant laser temperature regardless of the variation of environment temperature (
We present a complete set of mode-locked fiber lasers designed for photonic analog-to-digital conversion. Design, simulation, fabrication, and characterization of Er-doped fiber lasers are carried out through optimizing their performance to suit the requirements of high-speed and high-resolution photonic-assisted analog-to-digital converters. The required properties are achieved by active mode-locking on the basis of amplitude modulation of the cavity losses through a Mach–Zehnder modulator, and passive mode-locking on the basis of fast semiconductor saturable absorbers and intracavity polarizing fibers. The use of an intracavity polarizing fiber in combination with a fast saturable absorber allows dynamic control of the operation regimes through polarization control. Besides these oscillators designed with ring cavity structure, a short linear cavity with fundamental repetition frequency at the order of 1 GHz is studied, and an effective continuous tunability of the repetition frequency is obtained by an electromechanical transducer. Pulsed repetition rates up to 20 GHz, pulsewidths down to 500 fs, and time jitters below 180 fs are obtained.
Under proper injection of an incoming optical signal to be format-converted, a semiconductor laser can be driven at period-one dynamics due to the dynamical competition between the injection-imposed laser oscillation and the injection-shifted cavity resonance. Equally separated spectral components therefore emerge, the intensity and frequency of which strongly depend on the intensity and frequency of the incoming optical signal. Optical modulation format conversion between amplitude-shift keying (ASK) and frequency-shift keying (FSK) can thus be achieved by applying such a mechanism. The conversion depends solely on the property of the incoming optical signal for a given laser and therefore only a typical semiconductor laser is necessary as the key conversion unit. Due to the unique underlying mechanism, both ASK-to-FSK and FSK-to-ASK conversions can be achieved using the same system. The bit-error ratio at 10 Gb/s is observed down to
External-cavity lasers are usually used for chaos encryption in optical chaos-based communication systems. The external-cavity round-trip time (the time delay in the laser dynamics) is often regarded as an additional key to encode messages, which is a critical security parameter. The feasibility of identifying the time delay has been a crucial issue in chaotic optical communication. Some researchers propose that the time delay can be hidden by modulating the value of feedback strength or increasing the number of feedback cavities. In this paper, we experimentally and numerically demonstrate that the time delay signatures cannot be concealed in optical feedback semiconductor lasers. Whether single or double optical feedback, the time delay signatures can all be identified by the power spectrum analysis method. Furthermore, adjusting the feedback strength, the pumping current and the time-delay value, we find that the extraction of the time delay signatures still cannot be influenced.
Gold nanoparticles embedded in an optical gain material, particularly in a water solution of Rhodamine 6G, used in dye lasers can both increase and damp dye flourescence, thus changing the laser output intensity. Simultaneously, such nanoparticles influence the gain material's resistance against photobleaching. In this paper, we report our study on the impact of the