Reduce Intensity Noise Research Articles

Large-mode-area soliton fiber oscillator mode-locked using NPE in an all-PM self-stabilized interferometer.

In this work, we investigate an approach to scale up the output pulse energy in an all-polarization-maintaining 17.3 MHz Yb-doped fiber oscillator via implementation of a 25 µm core-diameter large-mode-area fiber. The artificial saturable absorber is based on a Kerr-type linear self-stabilized fiber interferometer, enabling non-linear polarization rotation in polarization-maintaining fibers. Highly stable mode-locked steady states in the soliton-like operation regime are demonstrated with 170 mW average output power and a total output pulse energy of ∼10n J distributed between two output ports. An experimental parameter comparison with a reference oscillator constructed with 5.5 µm core-sized standard fiber components reveals an increase of pulse energy by a factor of 36 with simultaneously reduced intensity noise in the high-frequency range >100k H z.

Use of external optical feedback to stabilize multimode hopping and reduce intensity noise in long-wavelength semiconductor laser

We report on the possibility of applying optical feedback (OFB) from a short external cavity to change the multimode hopping oscillation in long-wavelength semiconductor laser to single-mode oscillation. We characterize the influence of OFB on the modal oscillations and the associated noise spectrum of the multimode laser. The study is based on a modified time-delay multimode rate-equation model of the laser that includes mechanisms of spectral gain suppression along with OFB induced due to multiple reflections by an external reflector. The study is applied to 1.55 μm-InGaAsP laser that exhibits multimode hopping in its solitary version and supports wide bandwidth. The noise is evaluated in terms of the relative intensity noise. We show that strong OFB changes impact of the asymmetric gain suppression on the mode structure of the laser so that it changes the side mode suppression ratio (SMSR) and induces jumping of the strongest modes to longer or shorter wavelengths in random-like fashion. The change of SMSR of the laser occurs mainly when strong OFB induces multiperiodic and chaos oscillations. We specify the ranges of OFB over which SMO is induced. The low-frequency noise is lowest when the laser maintains CW operation or exhibits period-1 oscillations, while it is maximized when the laser dynamics are chaotic.

Intensity Noise Properties of Mid-Infrared Injection Locked Quantum Cascade Lasers: I. Modeling

In this paper, we numerically investigate the effect of optical injection locking on the noise properties of mid-infrared quantum cascade lasers. The analysis is carried out by means of a rate equation model, which takes into account the various noise contributions and the injection of the master laser. The obtained results indicate that the locked slave laser may operate under reduced intensity noise levels compared with the free running operation. In addition, optimization of the locking process leads to further suppression of the intensity noise when the slave laser is biased close to the free-running threshold current. The main factors that significantly affect the locking process and the achievable noise levels are the injected optical power and the master-slave frequency detuning.

Observation of squeezed light from one atom excited with two photons

Single quantum emitters such as atoms are well known as non-classical light sources with reduced noise in the intensity, capable of producing photons one by one at given times. However, the light field emitted by a single atom can exhibit much richer dynamics. A prominent example is the predicted ability of a single atom to produce quadrature-squeezed light, which has fluctuations of amplitude or phase that are below the shot-noise level. However, such squeezing is much more difficult to observe than the emission of single photons. Squeezed beams have been generated using macroscopic and mesoscopic media down to a few tens of atoms, but despite experimental efforts, single-atom squeezing has so far escaped observation. Here we generate squeezed light with a single atom in a high-finesse optical resonator. The strong coupling of the atom to the cavity field induces a genuine quantum mechanical nonlinearity, which is several orders of magnitude larger than in typical macroscopic media. This produces observable quadrature squeezing, with an excitation beam containing on average only two photons per system lifetime. In sharp contrast to the emission of single photons, the squeezed light stems from the quantum coherence of photon pairs emitted from the system. The ability of a single atom to induce strong coherent interactions between propagating photons opens up new perspectives for photonic quantum logic with single emitters.

DE-NOISING TECHNIQUE FOR VIBRATION SIGNALS OF ROTATING MACHINERY BASED ON MATHEMATICAL MORPHOLOGY FILTER

De-noising the vibration signal of rotating machinery realized based on mathematical morphology. New noise reduction technique based on open-closing and close-opening combined morphological filters proposed. The ability of morphological filter deals with different types of noise discussed. The method of FT combined morphological filter also proposeds to reduce intensity noise. Simulation and experiment example demonstrate the effectiveness of the algorithm. It is effective to filter the noises in vibration signal and improve S/N ratio prominently. The algorithm is fast and propitious to engineering.

Intensity noise in Brillouin fiber ring lasers

The intensity noise properties of Brillouin fiber ring lasers are investigated both theoretically and experimentally. The fluctuating parameters that have the dominant influence on laser intensity noise are the pump rate and the cavity reinjection rate. The transfer functions that relate the laser intensity noise to the fluctuations of these parameters are determined in a theoretical study that is performed within the framework of the usual three-wave model of stimulated Brillouin scattering. The theoretical predictions are confirmed by experiments performed in a Brillouin fiber ring laser operating in a low-finesse cavity. Finally, the ability of all-fiber Brillouin lasers to reduce intensity noise of pump sources is discussed.

Quantum noise of laser diodes

Single-mode laser theory for semiconductor lasers predicts sub-Poissonian light generation for a laser quietly driven far above threshold. Experiments have shown however that only few laser diodes exhibits such reduced intensity noise. We present a review of different mechanisms that have been proposed to explain the excess noise observed in semiconductor lasers, including imperfect anticorrelations in multimode lasers, and Petermann excess noise factor in single-mode lasers.

Effect of transmission through fiber gratings on semiconductor laser intensity noise

The effect of transmission through a fiber Bragg grating on the relative intensity noise of semiconductor laser light is investigated. We first present a model of the grating as a linear frequency discriminator that exchanges correlated power between frequency noise and intensity noise caused by spontaneous emission. This correctly explains observed increases in intensity noise of up to 30 dB at low frequencies, obeying an inverse-square frequency dependence. Next, we show that there exist conditions under which a grating can reduce intensity noise and that these are determined by the phase relationship between correlated intensity and frequency fluctuations. Finally, we demonstrate a 2 dB reduction of intensity noise at frequencies up to 15 GHz, and present a numerical calculation based on the complex transmittance of the grating that correctly describes the effect of grating dispersion.

Detection of methane in air using diode-laser pumped difference-frequency generation near 3.2 ?m

Spectroscopic detection of the methane in natural air using an 800 nm diode laser and a diode-pumped 1064 nm Nd:YAG laser to produce tunable light near 3.2 µm is reported. The lasers were pump sources for ring-cavity-enhanced tunable difference-frequency mixing in AgGaS2. IR frequency tuning between 3076 and 3183 cm−1 was performed by crystal rotation and tuning of the extended-cavity diode laser. Feedback stabilization of the IR power reduced intensity noise below the detector noise level. Direct absorption and wavelength-modulation (2f) spectroscopy of the methane in natural air at 10.7 kPa (80 torr) were performed in a 1 m single-pass cell with 1 µW probe power. Methane has also been detected using a 3.2 µm confocal build-up cavity in conjunction with an intracavity absorption cell. The best methane detection limit observed was 12 ppb m (Hz.)−1/2.

Intensity noise reduction in semiconductor lasers by amplitude-phase decorrelation

Detuned operation of a laser results in coupling of field amplitude and phase fluctuations. In a semiconductor laser, this coupling is known to be very large. We demonstrate that it can be used to significantly reduce intensity noise below its intrinsic limit.

Within mode quality and intensity changes of habituated stimuli

Habituation of skin conductanes response (SCR) magnitude was established by a number of presentations of a short burst of moderate intensity white noise. The 6th, 11th or 21st stimulus event was either a pure tone of unchanged loudness or another noise pulse of greatly reduced loudness. Mean SCR magnitude to the reduced intensity noise pulses was consistently smaller than that to the tones, but the difference of each of these responses from the habituation curve varied with the number of prior habituation trials. The qualitative changes in the stimulus produced a consistent increase in SCR magnitude; the greater the number of prior habituation trials, the larger the difference from the habituation curve. The reduced intensity noise stimulus reduced SCR magnitude below that of the habituation curve at the 6th trial, equalled the curve at the 11th trial, and yielded a greater response than the habituation curve at the 21st trial test position. The response to the tone was superior to that to the reduced intensity noise by a constant amount over the three habituation curve test points.