M. Vilera

High Power Three-Section Integrated Master Oscillator Power Amplifier at 1.5 μm

We present the design and the performance of a monolithically integrated master oscillator power amplifier at 1.5 μm. The three-section device includes a distributed feedback laser, a modulation section, and a high power tapered amplifier. In order to mitigate the coupling effects of the light reflected at the facets, the device has been designed with a bent longitudinal axis and a tilted front facet. The device delivers >400 mW mode-hopping free output power. In static regime, the modulation section allows an extinction ratio of 35 dB.

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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Fully integrated semiconductor master-oscillator power-amplifiers (MOPA) with a tapered power amplifier are attractive sources for applications requiring high brightness. The geometrical design of the tapered amplifier is crucial to achieve the required power and beam quality. In this work we investigate by numerical simulation the role of the geometrical design in the beam quality and in the maximum achievable power. The simulations were performed with a Quasi-3D model which solves the complete steady-state semiconductor and thermal equations combined with a beam propagation method. The results indicate that large devices with wide taper angles produce higher power with better beam quality than smaller area designs, but at expenses of a higher injection current and lower conversion efficiency.

m: Experiments and Theory

We study experimentally the dynamic properties of a fully integrated high power master-oscillator power-amplifier emitting at 1.5 μm under continuous wave and gain-switching conditions. High peak power (2.7 W) optical pulses with short duration (~ 110 ps) have been generated by gain switching the master-oscillator. We show the existence of working points at very close driving conditions with stable or unstable regimes caused by the compound cavity effects. The optical and radio-frequency spectra of stable and unstable operating points are analyzed.

Simulation and geometrical design of multi-section tapered semiconductor optical amplifiers at 1.57 μm

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.

Dynamic response of a monolithic master-oscillator power-amplifier at 1.5 µm

The beam properties of tapered semiconductor optical amplifiers emitting at 1.57 μm are analyzed by means of simulations with a self-consistent steady state electro-optical and thermal simulator. The results indicate that the self-focusing caused by carrier lensing is delayed to higher currents for devices with taper angle slightly higher than the free diffraction angle.

Modulation Performance of Three-Section Integrated MOPAs for Pseudorandom 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].

Analysis of the performance of tapered semiconductor optical amplifiers: role of the taper angle

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.

Modeling three-section master oscillator power amplifiers with a voltage driven traveling wave model

Semiconductor light sources like light emitting diodes (LEDs) or laser diodes (LDs) are the most important light sources for space applications. LEDs are used in the control panels or lightning systems in the spacecrafts and as growth lightning systems in a deep space.

Modulation characteristics of an integrated three-section master oscillator power amplifier at 1.5 μm

Nowadays the interest in high power semiconductor devices is growing for applications such as telemetry, lidar system or free space communications. Indeed semiconductor devices can be an alternative to solid state lasers because they are more compact and less power consuming. These characteristics are very important for constrained and/or low power supply environment such as airplanes or satellites. Lots of work has been done in the 800-1200 nm range for integrated and free space Master Oscillator Power Amplifier (MOPA) [1]-[3]. At 1.5 μm, the only commercially available MOPA is from QPC [4]: the fibred output power is about 700 mW and the optical linewidth is 500 kHz. In this paper, we first report on the simulations we have done to determine the appropriate vertical structure and architecture for a good MOPA at 1.58 μm (section II). Then we describe the fabrication of the devices (section III). Finally we report on the optical and electrical measurements we have done for various devices (section IV).