Antonio Pérez-Serrano

Spectral Delay Algebraic Equation Approach to Broad Area Laser Diodes

In this study, we discuss an efficient modeling approach for the simulation of broad-area laser diodes. Our method is based on folding the longitudinal propagation dimension into time delays which extend to the lateral dimension and to the influence of diffractive terms the idea of mesh decimation as it is discussed in . We compare the results of the dynamics obtained with our improved model that consists of coupled delay algebraic equations with the results of a standard traveling wave description in the cases of straight current stripes as well as in the important configuration of high-power tapered antireflection coated devices. We obtain an excellent agreement and an improvement of the integration time between one and two orders of magnitudes which may alleviate in some cases the necessity of using complex parallel codes.

Analysis of a random modulation single photon counting differential absorption lidar system for space-borne atmospheric CO 2 sensing

The ability to observe the Earths carbon cycles from space provides scientists an important tool to analyze climate change. Current proposed systems are mainly based on pulsed integrated path differential absorption lidar, in which two high energy pulses at different wavelengths interrogate the atmosphere sequentially for its transmission properties and are back-scattered by the ground. In this work an alternative approach based on random modulation single photon counting is proposed and analyzed; this system can take advantage of a less power demanding semiconductor laser in intensity modulated continuous wave operation, benefiting from a better efficiency, reliability and radiation hardness. Our approach is validated via numerical simulations considering current technological readiness, demonstrating its potential to obtain a 1.5 ppm retrieval precision for 50 km averaging with 2.5 W average power in a space-borne scenario. A major limiting factor is the ambient shot noise, if ultra-narrow band filtering technology could be applied, 0.5 ppm retrieval precision would be attainable.

Wavelength Jumps and Multimode Instabilities in Integrated Master Oscillator Power Amplifiers at 1.5

We analyze the large (>10 nm) and abrupt jumps in emission wavelength, together with the multimode instabilities associated with them, which are observed in monolithically integrated master oscillator power amplifiers emitting at 1.5 μm. The physical origin of such phenomena is investigated in the framework of a travelling-wave model which phenomenologically incorporates thermal effects via self and cross-heating of the different sections of the device. The occurrence of the wavelength jumps and the instabilities as a function of the injected currents in the two sections is interpreted in terms of a thermally tuned competition between the modes of the master oscillator and the compound cavity modes.

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We theoretically study all-optical simultaneous wavelength conversion of multiple channels by four-wave mixing in semiconductor ring lasers. Locking the semiconductor ring laser to a holding beam allows us to achieve large conversion efficiencies with good signal-to-noise ratio in several channels at multi-Gb/s bit rates. Cross-talk between signals, arising from the peculiar four-wave mixing cascade of modes in semiconductor ring lasers and their cross-gain saturation, is studied in detail. We show that it can be controlled by adjusting the intensity of the holding beam, the bias current of the laser, and the number, intensity, and wavelength of signals that one wants to convert.

m: Experiments and Theory

We propose an integrated path differential absorption (IPDA) lidar system based on a hybrid master oscillator power amplifier (MOPA) and single photon counting detection for column-averaged measurements of atmospheric CO2. The random modulated continuous wave (RM-CW) approach has been selected as the best suited to the average output power obtained from hybrid and monolithically integrated MOPAs. A compact RM-CW IPDA lidar instrument has been designed and fabricated. High-sensitivity and low-noise single photon counting has been used for the receiver. Colocated 2-km horizontal trial path experiments with a pulsed system and in situ measurements were performed for comparison. The RM-CW IPDA lidar instrument shows a relative accuracy of the order of about ±10% or ±40 parts per million CO2 concentration in absolute terms. The measurements qualitatively demonstrate the feasibility of CO2 IPDA measurements with an RM-CW system.

Multichannel Wavelength Conversion Using Four-Wave Mixing in Semiconductor Ring Lasers

We propose an integrated path differential absorption lidar system based on all-semiconductor laser sources and single photon counting detection for column-averaged measurements of atmospheric CO2. The Random Modulated Continuous Wave (RM-CW) approach has been selected as the best suited to semiconductor lasers. In a RM-CW lidar, a pseudo random sequence is sent to the atmosphere and the received signal reflected from the target is correlated with the original sequence in order to retrieve the path length. The transmitter design is based on two monolithic Master Oscillator Power Amplifiers (MOPAs), providing the on-line and off-line wavelengths close to the selected absorption line around 1.57 µm. Each MOPA consists of a frequency stabilized distributed feedback master oscillator, a bent modulator section, and a tapered amplifier. This design allows the emitters to deliver high power and high quality laser beams with good spectral properties. An output power above 400 mW with a SMSR higher than 45 dB and modulation capability have been demonstrated. On the side of the receiver, our theoretical and experimental results indicate that the major noise contribution comes from the ambient light and detector noise. For this reason narrow band optical filters are required in the envisioned space-borne applications. In this contribution, we present the latest progresses regarding the design, modeling and characterization of the transmitter, the receiver, the frequency stabilization unit and the complete system.

Atmospheric CO

The accurate determination of the atmospheric distribution of carbon dioxide (CO2) on planetary scale is a key requirement for setting up modeling tools able to make reliable predictions of Earth climate dynamics which are essential for the understanding of such important issues as climate change and global warming. Nowadays, the concentrations of CO2 are mainly measured in-situ at a number of surface stations that are unevenly distributed over the planet. Air-borne and space-borne missions have the potential to provide a denser and better distributed set of observations to complement those provided by the surface network.

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The suitability of a three-section master oscillator power amplifier for pseudorandom lidar is investigated by means of the experimental characterization and analysis of its emission characteristics under modulation. The proposed architecture consists of a distributed feedback laser, a modulation section, and a tapered semiconductor optical amplifier. The modulation section acts as an absorber or amplifier when driven at zero or positive bias. Under pseudorandom modulation at 25 Mb/s, a high optical modulation amplitude and extinction ratio were achieved. The characterization of the emission spectra under modulation revealed typical features of frequency modulation due to the carrier-induced refractive index changes.

Sensing with a Random Modulation Continuous Wave Integrated Path Differential Absorption Lidar

Numerous applications such as free space optical communications, metrology and differential absorption lidar systems require high brightness laser sources with spectral purity. Monolithically integrated Master Oscillator Power Amplifiers (MOPAs) are promising candidates to fulfil these requirements. In particular, a three-section bent mOpA at 1.5 μm was recently proposed as laser source for an integrated path differential absorption lidar system for measurement of atmospheric CO2 [1]. The device consists of a distributed feedback (DFB) section acting as master oscillator, a bent modulator (MOD) section and a tapered semiconductor optical amplifier (SOA) section with a tilted front facet to avoid coupled cavity effects [2]. Three separate electrical contacts on the laser chip provide access to the three sections: the DFB current controls the laser emission frequency, the MOD current allows for modulation and the SOA current drives the amplification. The MOD section acts as an absorber or amplifier when driven at zero or positive voltage bias respectively. Complete output extinction requires negative values of the MOD current due to carrier generation caused by the power injected from the DFB into the MOD section [1].

Atmospheric CO2 remote sensing system based on high brightness semiconductor lasers and single photon counting detection

High brightness semiconductor laser sources with modulation capacity are emerging candidates for an increasing number of applications. We have recently presented an integrated three section Master Oscillator Power Amplifier (MOPA) [1] to be used in space-borne Random Modulated Continuous Wave (RM-CW) Integrated Path Differential Absorption (IPDA) lidar systems for atmospheric CO2 detection [2]. The application requires a stable single-mode emission spectrum, high power and beam quality, together with internal modulation capacity at 25 Mb/s.