Intrinsic Chirp Research Articles

Cosmic equation of state and advanced LIGO-type gravitational wave experiments

Future generation of interferometric gravitational wave detectors is hoped to provide accurate measurements of the final stages of binary inspirals. The sources probed by such experiments are of extragalactic origin and the observed chirp mass is the intrinsic chirp mass multiplied by $(1+z)$ where $z$ is the redshift of the source. Moreover the luminosity distance is a direct observable is such experiments. This creates the possibility to establish a new kind of cosmological tests, supplementary to more standard ones. Recent observations of distant type Ia supernovae light-curves suggest that the expansion of the universe has recently begun to accelerate. A popular explanation of present accelerating expansion of the universe is to assume that some part $\Omega_Q$ of the matter-energy density is in the form of dark component called ``the quintessence'' with the equation of state $p_Q = w \rho_Q$ with $w \geq -1.$ In this paper we consider the predictions concerning observations of binary inspirals in future LIGO type interferometric experiments assuming a ``quintessence cosmology''. In particular we compute the expected redshift distributions of observed events in the a priori admissible range of parameters describing the equation of state for the quintessence. We find that this distribution has a robust dependence on the cosmic equation of state.

Pulse compression of a high-order harmonic

The fifth harmonic pulses of an intense femtosecond Ti:sapphire laser were experimentally shown to be negatively chirped by using an LiF plate as a positive dispersive medium. The chirp of the harmonic pulse originates from the intensity-dependent atomic dipole phase, which is estimated to be proportional to 25 Up, where Up is the ponderomotive energy. Consequently, we have succeeded in compressing the chirped pulses to 13 fs by compensating the intrinsic negative chirp. Chirp effects of the fundamental laser on the pulse width of the fifth harmonic were consistent with the negative chirp of the fifth harmonic.

Pulse Compression of a High-Order Harmonic by Compensating the Atomic Dipole Phase

The fifth harmonic pulses of an intense femtosecond Ti:sapphire laser are experimentally shown to be negatively chirped by using a LiF plate as a positive dispersive medium. The chirp of the harmonic pulse is originated from the intensity-dependent atomic dipole phase, which is estimated to be proportional to ${25U}_{p}$, where ${U}_{p}$ is the ponderomotive energy. Consequently, we have succeeded in compressing the chirped pulses to 13 fs by compensating the intrinsic negative chirp. Chirp effects of the fundamental laser on the pulse width of the fifth harmonic were also investigated.

Precise measurement of semiconductor laser chirp using effect of propagation in dispersive fiber and application to simulation of transmission through fiber gratings

Measurements of small-signal intensity modulation from direct-modulated distributed feedback (DFB) semiconductor lasers after propagation in dispersive fiber have previously been used to extract intrinsic laser chirp parameters such as linewidth enhancement factor and crossover frequency. Here, we demonstrate that the simple rate equations do not satisfactorily account for the frequency response of real DFB lasers and describe some experimental techniques that conveniently determiner the precise laser chirp. Implications for simulation of high-speed lightwave systems are also considered.

Cosmological constant and advanced gravitational wave detectors

Interferometric gravitational wave detectors could measure the frequency sweep of a binary inspiral [characterized by its chirp mass] to high accuracy. The observed chirp mass is the intrinsic chirp mass of the binary source multiplied by $(1+z)$, where $z$ is the redshift of the source. Assuming a non-zero cosmological constant, we compute the expected redshift distribution of observed events for an advanced LIGO detector. We find that the redshift distribution has a robust and sizable dependence on the cosmological constant; the data from advanced LIGO detectors could provide an independent measurement of the cosmological constant.

Chirp and system performance of integrated laser modulators

Time-resolved chirp measurements and laser-threshold measurements are used to understand the chirp performance of integrated laser electroabsorption modulators. The different effects of the intrinsic modulator chirp component and chirp caused by optical feedback, from reflection at the output facet into the laser, are observed. A figure of merit is introduced to assess the chirp performance, which shows good correlation with dispersion penalty measurements. The effect of reflection-induced chirp is considerably reduced by operating the modulator with negative chirp. An optimized device is reported, which delivers purely negative chirp with reasonable optical power. >

Injection-seeding and self-injection-seeding of gain-switched Fabry-Pérot laser diodes

We present a simple model which allows us to predict the spectral behaviour of gain-switched Fabry-Perot (F-P) laser diodes submitted to a weak quasi-monochromatic cw (or pulsed) injection signal. Different experiments are reported for illustration, some of them being new. The model describes the competition between the injection-driven field and the spontaneousnoise driven field during pulse build-up. The relative amplitudes of the two fields are evaluated at the gains-witching time as well as the spectral content of the injection-driven field. Different types of modal selection are found depending on the injection conditions. In the case of cw injection, there is a wide range of injection frequencies leading to single-mode emission, but two-mode lasing is also predicted for lasers exhibiting strong intrinsic chirp. These results are confirmed in experiments carried out on a 1.5 μm Fabry-Perot laser driven by different cw dfb injection lasers. In the case of pulsed injection, the laser behaviours are similar but the model also shows the influence of the pulsed-injection arrival time on the mode selection process. This is experimentally illustrated in the case of a pulsed 1.3 μm laser operated in self-injection, the injected signal resulting from a weak spectrally-filtered optical feedback.