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).
presented. The proposed tool is addressed to the students of optical communication courses, encouraging self consolidation of the subjects learned in lectures. The semiconductor laser model is based on the well known rate equations for the carrier density, photon density and optical phase. The direct modulation of the laser is considered with input parameters which can be selected by the user. Different options for the waveform, amplitude and frequency of the injected current are available, together with the bias point. Simulation results are plotted for carrier density and output power versus time. Instantaneous frequency variations of the laser output are numerically shifted to the audible frequency range and sent to the computer loudspeakers. This results in an intuitive description of the “chirp” phenomenon due to amplitude-phase coupling, typical of directly modulated semiconductor lasers. In this way, the student can actually listen to the time resolved spectral content of the laser output. By changing the laser parameters and/or the modulation parameters, consequent variation of the laser output can be appreciated in intuitive manner. The proposed educational tool has been previously implemented by the same authors with locally executable software. In the present manuscript, we extend our previous work to a web based platform, offering improved distribution and allowing its use to the wide audience of the web.
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.
Integrated master-oscillator power amplifiers driven under steady-state injection conditions are known to show a complex dynamics resulting in a variety of emission regimes. We present experimental results on the emission characteristics of a 1.5 μm distributed feedback tapered master-oscillator power-amplifier in a wide range of steady-state injection conditions, showing different dynamic behaviors. The study combines the optical and radio-frequency spectra recorded under different levels of injected current into the master oscillator and the power amplifier sections. Under low injection current of the master oscillator the correlation between the optical and radio-frequency spectral maps allows to identify operation regimes in which the device emission arises from either the master oscillator mode or from the compound cavity modes allowed by the residual reflectance of the amplifier front facet. The quasi-periodic occurrence of these emission regimes as a function of the amplifier current is interpreted in terms of a thermally tuned competition between the modes of the master oscillator and the compound cavity modes. Under high injection current of the master oscillator, two different regimes alternate quasi-periodically as a function of the injected current in the power amplifier: a stable regime with a single mode emission at the master oscillator frequency, and an unstable and complex self-pulsating regime showing strong peaks in the radio-frequency spectra as well as multiple frequencies in the optical spectra.
We have studied experimentally and theoretically the nonlinear dynamics of a 1550 nm single transverse mode VCSEL subject to two-frequency orthogonal optical injection. In this type of injection both injected fields have a linear polarization that is orthogonal to that of the free-running VCSEL. We have found different behaviors that include irregular and periodic dynamics in the orthogonal polarization, periodic dynamics in both linear polarizations and a situation in which both linearly polarized modes lock to the most intense injection when its wavelength is close to the free-running laser wavelength. In this study we also analyze the generated high-frequency microwave signal found when the VCSEL is emitting only in the orthogonal polarization. The relative strength of peaks in the optical spectra at the frequencies of both master lasers depends on the behaviour of the VCSEL under single optical injection by the most intense master laser. The peak in the optical spectrum that appears at the frequency of the most intense master laser is larger than the peak that appears at the frequency of the other master laser, providing that there is stable locking when only light from the most intense laser is injected. In this case a significant emission of the VCSEL at the frequency of the most intense master laser is observed. On the contrary, if there is not stable locking when only light from the most intense laser is injected, the magnitude of both peaks becomes similar and a significant emission of the VCSEL at the frequency of the weakest master laser is observed. Good agreement is found between our experimental and theoretical results.
The availability of suitable laser sources is one of the main challenges in future space missions for accurate measurement
of atmospheric CO2. The main objective of the European project BRITESPACE is to demonstrate the feasibility of an
all-semiconductor laser source to be used as a space-borne laser transmitter in an Integrated Path Differential Absorption
(IPDA) lidar system. We present here the proposed transmitter and system architectures, the initial device design and the
results of the simulations performed in order to estimate the source requirements in terms of power, beam quality, and
spectral properties to achieve the required measurement accuracy. The laser transmitter is based on two InGaAsP/InP
monolithic Master Oscillator Power Amplifiers (MOPAs), providing the ON and OFF wavelengths close to the selected
absorption line around 1.57 μm. Each MOPA consists of a frequency stabilized Distributed Feedback (DFB) master
oscillator, a modulator section, and a tapered semiconductor amplifier optimized to maximize the optical output power.
The design of the space-compliant laser module includes the beam forming optics and the thermoelectric coolers. The
proposed system replaces the conventional pulsed source with a modulated continuous wave source using the Random
Modulation-Continuous Wave (RM-CW) approach, allowing the designed semiconductor MOPA to be applicable in
such applications. The system requirements for obtaining a CO2 retrieval accuracy of 1 ppmv and a spatial resolution of less than 10 meters have been defined. Envelope estimated of the returns indicate that the average power needed is of a
few watts and that the main noise source is the ambient noise.
We experimentally investigate high-frequency microwave signal generation using a 1550 nm single-mode VCSEL subject to two-frequency optical injection. We first consider a situation in which the injected signals come from two similar VCSELs. The polarization of the injected light is parallel to that of the injected VCSEL. We obtain that the VCSEL can be locked to one of the injected signals, but the observed microwave signal is originated by beating at the photodetector. In a second situation we consider injected signals that come from two external cavity tunable lasers with a significant increase of the injected power with respect to the VCSEL-by-VCSEL injection case. The polarization of the injected light is orthogonal to that of the free-running slave VCSEL. We show that in this case it is possible to generate a microwave signal inside the VCSEL cavity.
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.
High power two-section tapered lasers are promising candidates to generate short optical pulses by Q-switching. The
main advantage of these devices is that high peak optical power can be generated by using a low excitation current in the
ridge-waveguide section. In this work we analyze the Q-switching dynamics of two-section tapered lasers by means of a
simplified three-rate-equation model and we compare the results with measurements in 1060 nm DBR multi/section
tapered lasers. The experiments and simulations show similar trends with repetition frequency, modulation signal
amplitude and bias conditions. The effect of the driving conditions on the peak power and pulse duration is analyzed.
100 ps pulses with 4.2 W peak power are obtained at 900 MHz repetition frequency.
We present results on the electrical characterization of commercial fiber pigtailed 1. 55 μm 2.5 Gb/s VCSEL based on
InAlGaAs active region, tunnel junction (TJ), air-gap aperture and InAlGaAs/InAlAs mirrors. The current-voltage (I-V)
characteristics were measured and the results were fitted to the analytical expressions of an equivalent circuit considering
the TJ in series with the active junction and a series resistance. Carrier capture/escape effects were considered in order to
account for the reduced value of the drop in the measured differential resistance at threshold. The electrical parameters of
both junctions were determined, showing that the TJ was responsible for most of the voltage drop at threshold. High
frequency electrical impedance measurements were used to determine internal parameters as well as the role of external
parasitics. The results were analyzed using a small signal equivalent circuit which includes the TJ, carrier capture/escape
effects, the cavity parasitics, and the electrical access. A good agreement between the experimental and the equivalent
circuit impedances at different bias was obtained by considering the differential resistances of the active and tunnel
junctions extracted from the I-V characteristics, yielding reasonable values of the dynamic time constants and of the
recombination coefficients.
We report an experimental and theoretical investigation of the effect of optical injection on the characteristics of optical
pulses generated by gain-switching a 1550 nm single transverse mode vertical-cavity surface-emitting laser (VCSEL).
Under continuous wave operation the VCSEL emits in a linear polarization along the whole current range. The
experimental analysis of the effect of external optical injection on the timing jitter, maximum power, and pulse width of
optical pulses generated by gain-switching the single mode VCSEL is performed for several repetition rates and for
different values of the detuning between the frequency of the optical injection and the VCSEL. Experimental results
show that for 1 GHz repetition frequency, jitter reductions greater than 70 % can be obtained over a 47 GHz frequency
detuning range with a slight increase of 22% in pulse width with respect to the solitary case. A clear anticorrelation
between the maximum power and pulse width is also obtained. A theoretical study is also performed by using a model
that incorporates both spatial dependence of carrier density and optical field profiles. The two polarization modes are
also taken into account in the model. The theoretical results are in good agreement with the experimental results.
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