Cooperative emission due to spontaneous build-up and rapid decay of macroscopic polarization in a strongly inverted gain medium is drastically different from the lasing dynamics. The medium polarization and not the cavity field drives the emission from a device in semiclassical Maxwell-Bloch picture. Yet as pioneered by Dicke, the decay of the highest-energy state in a quantum ensemble of two-level systems proceeds through a ladder of the highest-symmetry partially deexcited states, each of which is formalistically an entangled state in mathematical sense. In this paper we summarize our experimental and theoretical studies on the two fundamental aspects of superradiance in multi-section tandem cavity laser heterostructures: (i) How can the superradiance be reached in semiconductor quantum wells albeit the ultrafast dephasing of individual microscopic e-h dipoles? (ii) Could the ensemble non-classicality be transferred to the emitted optical field and what could be the resulting photon state?
In the area of smart mobility, a major challenge is to insure secure transportation. LIDAR are acknowledged as key enablers for Advanced Driver Assistance Systems (ADAS) and autonomous driving. Our approach for the Time of Flight (ToF) LIDAR is to use an Optical Phase Array (OPA), for the optical beam steering, together with a high peak power and high beam quality laser diode emitting at 905nm. To the best of our knowledge, a high-power laser diode at 905nm directly compatible with an OPA does not exist. We report on the design, realization and characterization of laser diode, with different geometries, emitting several watts (>10W) in a short pulse (typically 10ns) operation, in order to be coupled into the silicon nitride waveguide input of the OPA developed by the CEA LETI. The high power 905nm LASER coupled into the OPA, and their respective drivers, will constitute the optical steerable source, without no moveable parts, of the medium range TOF LIDAR developed within the European VIZTA project. The Aluminum free active region laser structure have been grown by Metal Organic Vapor Phase Epitaxy (MOVPE) on 3” GaAs substrates. It contains a single GaInAsP compressively strained Quantum Well (QW) for emission at 905nm, located in a GaInP waveguide. This structure exhibits high internal quantum efficiency ηqi of 0.99, low internal losses αi of 1.3cm-1 and low transparency current density J0 of 59A/cm2. Peak optical powers of 11.4W at 15.4A and 7.7W at 10.2A are obtained, respectively, for two different geometries.
We report a novel ultra-short light pulse emitters utilizing transient charge carrier behaviour in a multiple wide-quantumwell (WQW) heterostructure. The optical waveguide is implemented as a tandem-cavity laser diode with electro absorber section in the middle, surrounded by two end-firing gain sections. The ultrashort pulse production is achieved by employing the gain region with three wide GaAsP tensile strained quantum wells separated by GaInP barriers in an unintentionally doped active region of the p-i-n laser diode structure. At large negative absorber bias, lasing emission spiking starts with an unusually long delay of 7 μs. By applying the current pulses of duration smaller than 7 μs it is possible to quench entirely the lasing emission. With selection of the parameters of the electrical pump pulse and the absorber voltage it is possible to obtain ultra-short light pulse regime. This optical pulse appears at the end of the electrical pump pulse, as a single optical pulse on top of wide pedestal, due to amplified spontaneous emission. The duration of the pulse is 1.2 ps and pulse energy is 80 pJ. We attribute this behaviour to quantum confined Stark effect. Removal of the external bias field, enabling stronger overlap of carriers yields a sudden increase in the radiative recombination rate and optical gain enabling SR emission. We provide a detailed report on the pulse width and optical spectral behaviour as well as on possible nonclassical correlation in the emitted light state seen from comparison to CW lasing regime.
European Space Agency (ESA) considers Mode-Locked Semi-Conductor Lasers as a promising technology for precision metrology systems in space such as High Accuracy Absolute Long Distance Measurement. We report our progress towards challenging ESA requirements: picosecond pulse duration, pulse energy 200 pJ, Pulse Repetition Frequency (PRF) 1-3 GHz, PRF stability < 5·10-9 at 1 second and PRF tunability 20 MHz. The laser should have small power consumption, be compact and robust against launch vibrations. We have reported in the past two such mode-locked (ML) laser diodes, each reaching only 90 pJ pulse energies: (i) very long (13.5mm) monolithic tapered laser and (ii) inverse bow-tie external cavity (EC) laser. The subject of the present communication is a novel passively mode-locked monolithic tapered laser achieving 201 pJ pulses. Large optical cavity with 2QWs heterostructure provides a low internal loss (~1 cm-1) together with high quantum efficiency (< 90 %) and low series resistance. To reach high energy output pulses, the tapered gain section gets a low (< 0.1 %) reflectivity dielectric coating. For passive mode-locking at fundamental cavity frequency, the saturable electroabsorber section is located at the back side of the gain chip with a high reflectivity coating (< 95 %). The monolithic cavity is made 13.5mm long by introducing an intermediate section for PRF tuning around 3 GHz. We reached passive ML at 2.9 GHz PRF with pulse energy of 201 pJ, compressed pulse width of 2.6 ps and electric power consumption of 8.2 W. PRF can be continuously tuned by 9.8 MHz. Active current modulation for hybrid ML resulted in PRF relative stability at 9.16·10-10 level on 1s intervals, while with a phase lock loop (PLL) acting on the DC gain section current we reached PRF stability of 1.15·10-10 on 1 s measurement interval.
We report on multi-section inverse bow-tie laser producing mode-locked pulses of 90 pJ energy and 6.5 ps width (895 fs after compression) at 1.3 GHz pulse repetition frequency (PRF) and consuming 2.9 W of electric power. The laser operates in an 80 mm long external cavity. By translation of the output coupling mirror, the PRF was continuously tuned over 37 MHz range without additional adjustments. Active stabilization with a phase lock loop actuating on the driving current has allowed us to reach the PRF relative stability at a 2·10-10 level on 10 s intervals, as required by the European Space Agency (ESA) for inter-satellite long distance measurements.
Time and Frequency applications need high accuracy and high stability clocks. Optically pumped compact industrial Cesium atomic clocks are a promising approach that could satisfy these demands. However, the stability of these clocks relies, among others, on the performances of the laser diodes that are used. This issue has led the III-V Lab to commit to the European Euripides-LAMA project that aims to provide competitive compact optical Cesium clocks for ground applications. This work will provide key experience for further space technology qualification. III-V Lab was in charge of the design, fabrication and reliability of Distributed- Feedback diodes (DFB) at 894 nm (D1 line of Cesium) and 852 nm (D2 line). The use of D1 line for pumping will provide simplified clock architecture compared to the D2 line pumping thanks to simpler atomic transitions and a larger spectral separation between lines in the 894 nm case. Also, D1 line pumping overcomes the issue of unpumped “idle states” that occur with D2 line. The modules should provide narrow linewidth (<1 MHz), very good reliability in time and, crucially, be less sensitive to optical feedback. We show here results from Al-free active region with InGaAsP quantum well Ridge DFB lasers. We obtain the D1 Cs line (894.4nm) at 67°C and 165mA (optical power of 40mW) with a high side mode suppression ratio. The D2 Cs line (852.1nm) is obtained at room temperature at 40mW. By a small increase of temperature it is also possible to get Cs lines at 20mW. In order to address the long term reliability of these lasers, long duration ageing tests (more than one year targeted) have been carried out for both wavelengths at 20mW and 25°C The laser diodes have aged during 10 000 hours and 9336 hours for DFB addressing Cesium D2 and D1 lines, respectively. These ageing tests show very low increase of the operating current, almost linear with time. Lasers designed for D1 and D2 Cesium lines show an average increase of operating current of 0.15% and 0.37% per 1000hours, respectively.
Mode-locked semiconductor laser technology is a promising technology candidate considered by European Space Agency (ESA) for optical metrology systems and other space applications in the context of high-precision optical metrology, in particular for High Accuracy Absolute Long Distance Measurement. For these applications, we have designed, realized and characterized a multi-section monolithic-cavity tapered laser diode with a record cavity length of 13.5mm. The laser operates at 975nm wavelength with average output power up to 600mW. It is based on a MOVPE grown laser structure with Aluminium free active region enabling high optical gain, low internal losses and low series resistance. It reaches passive mode-locking operation on fundamental cavity round trip frequency of 2.88GHz with chirped pulse width of 6.2ps and time bandwidth product of 8 for the average output power of 250mW. Alongside with passive mode-locking operation, we discuss other lasing regimes in these very long tapered lasers.
Time-frequency applications need high accuracy and high stability clocks. Compact industrial optically pumped Cesium beam standards are promising to address various demands. In this context we are developing Al-free active region distributed-feedback diode (DFB) lasers at 852nm and 894nm for, respectively, the D2 and D1 line Cesium pumping. In order to address the long term reliability of these lasers, long duration ageing tests (more than one year targeted) are being carried out for both wavelengths at 20mW and 25°C. The laser diodes have been ageing for 4950 hours and 3120 hours respectively with very low increase of the operating current.
Mode-locked semiconductor laser technology is a promising technology candidate considered by European
Space Agency (ESA) for optical metrology systems and other space applications in the context of high-precision
optical metrology, in particular for High Accuracy Absolute Long Distance Measurement. For these
applications, we have realised a multi-section monolithic-cavity tapered laser diode with a record cavity
length of 13.5 mm. The laser operates at 975 nm wavelength. It is designed for the emission of ultra-short
optical pulses (<1 ps) at a repetition rate of 3 GHz with an average optical power of 600 mW. It is based on a
MOVPE grown laser structure with Aluminium free active region enabling high optical gain, low internal
losses and low series resistance. The first results obtained under CW pumping of such centimetre-long laser at
20 °C heatsink temperature show the lasing threshold current as low as 1.27 A and the differential external
efficiency as high as 0.55 W/A.
Due to the narrow absorption peak of Yb in glass at 975nm, a wavelength stabilisation is necessary for pump laser diodes. Our original approach is to use a Distributed Feedback broad area structure which is made possible since we use an Aluminium free active region laser structure. The target is to obtain high optical power of 10W with both a reduce wavelength evolution with temperature and a low spectral width. On a 3mm x 100 μm BA Fabry Perot laser, we have obtained a high power of 10W. Design, fabrication and results on BA DFB lasers will be presented, showing a low spectral width at 976nm at 3W output power.
The development of techniques such as atom optical pumping, for atomics clocks or precise gyroscopes, requires
laser diodes with high power and excellent spectral (narrow linewidth) and spatial qualities together with high
reliability.
We have realized a six months ageing test on Al-free DFB lasers emitting at 852nm for Cs pumping. Ten DFB
lasers were aged at 40°C and 20mW. The extrapolated lifetimes at 40°C, based on 20mW operating current, of
our DFB lasers are higher than 500000 hours which confirms the excellent potential of this Al-free technology
for long life spatial mission. Furthermore, the evolution of the operating current (initially around 70mA), after
six months, is less than 5% (corresponding to 3mA).
We obtain a very good stability of optical spectra: an average variation of the Side Mode Suppression Ratio
(SMSR) of less than 2dB and a variation of the wavelength of less than 0.12 nm.
We also measured the linewidth of our DFB lasers with the delayed self-heterodyne method after the six months
ageing: we obtain a very narrow linewidth at 25°C (measurement temperature) around 215kHz (lorentzian fit,
white noise) or 330kHz (gaussian fit, 1/f noise).
Precise gyroscopes and atomic clocks are in high demand for positioning and flight navigation systems or measurement
of fundamental constants. The development of techniques such as atom optical pumping (Cs or Rb) requires laser diodes
with high power and excellent spectral (narrow linewidth) and beam qualities. For spatial applications a high reliability is
required (mission lifetime is around 15 years).
We have realized different studies of reliability on our Al-free DFB lasers: Catastrophically Optical Mirror Damage
(COMD) evaluation, lifetest, optical and spectral measurements before and after ageing. We obtained high COMD
densities (respectively 13MW/cm2 in continuous wave CW and 19MW/cm2 in pulsed mode. Furthermore, we have
realized ageing test on these DFB laser diodes emitting at 852.12nm (D2 line of Cs). We used five different ageing
conditions (power and temperature) to determine ageing properties.
The extrapolated lifetimes of our DFB laser (for operating current variation equal to 100%) are higher than 140000 hours
(about 15 years) for an ageing at T= 25°C and P= 40mW. This confirms the excellent potential of this Al-free technology
for long life spatial mission.
The Side Mode Suppression Ration (SMSR) of the aged D2 line DFB lasers remains very high with a measured change
of -1.4dB ± 8dB. There are no significant drifts of the DFB laser wavelength after aging (average ~0.03 nm).
We also measured the linewidth of our aged DFB lasers by the self-heterodyne technique and obtained narrow beating
linewidths of around 900kHz.
F. Lelarge, R. Brenot, B. Rousseau, F. Martin, G. Patriarche, F. Poingt, L. LeGouezigou, O. Le Gouezigou, C. Dernazaretian, E. Derouin, O. Drisse, F. Pommereau, A. Accard, M. Caligaro, D. Make, J.-G. Provost, P. Resneau, B. Dagens, F. van-Dijk, M. Krakowski, G. H. Duan
We report on the recent advances in InP-based Quantum Dashes (Qdashes) material for 1.55μm optoelectronic devices.
We achieve highly uniform, reproducible and wavelength-controlled Qdashes, with a length ranging from 50nm to
500nm depending on the growth conditions. These Qdashes lead either to high modal gain distributed feedback (DFB)
lasers or low chirp semiconductor optical amplifier (SOA). Moreover, we demonstrate that Qdashes are compatible with
buried ridge stripe and shallow ridge technology and lead to very reliable lasers. Directly modulated lasers with 10GHz
bandwidth are demonstrated in continuous wave mode operation. 10Gb/s transmission over 25km in semi-cooled
operation is achieved using DFB buried lasers. Qdashes optimization leads to SOA with internal gain of 10 dB and a -3dB optical bandwidth of 120 nm at 50°C, paving the way for semi-cooled CWDM optical sources. Furthermore, low
chirp Qdashes SOA are evaluated as optical boosters after a modulated source. Although we still observe overshoots on
the amplified signal, the chirp, even in their saturation regime, is low enough to allow for 50 km of transmission at
10Gb/s.
We present high precision intensity noise measurements of Quantum Dot Superluminescent LEDs and lasers
emitting at 1.3μm. For the QD-SLEDs we investigate the intensity noise behavior and identify the relevant
noise parameters by comparing the experimental results to theoretical calculations. We find an Excess Noise
behavior due to amplified spontaneous emission, the dominant origin of noise. The investigation of the spectrally
resolved emission enables further characterization of the noise properties. The influence of a resonator on the
noise behavior is discussed for QD-Lasers. The noise of the laser is compared to the SLED's, and shows strong
deviation from the Excess Noise character above threshold.
We have developed 1.3 μm quantum dots (Qdot) using a dot in a well (DWELL) structure based on GaAs and 1.55 μm quantum dash (Qdash) based on InP Fabry-Perot lasers using a ridge waveguide operating in continuous wave at room temperature. The quantum dot lasers have demonstrated high power of 135 mW per facet and 50 mW per facet for the quantum dash devices. We have obtained very low relative intensity noise (RIN) with a nearly flat spectrum, around -159 dB/Hz ± 2 dB/Hz within 0.1-10 GHz range for the quantum dots and -160 dB/Hz ± 2 dB/Hz over a wide bandwidth from 50 MHz to 18 GHz for the quantum dash lasers. Recent experimental results are presented and analysed especially those relating to the noise performances and reliability tests to demonstrate the suitability of these new devices for microwave optical links.
During the European project, BIGBAND, we have developed 1.55 μm quantum dash Fabry-Perot lasers based on InP using a ridge waveguide operating in continuous wave at room temperature. These devices have not only reached a high power of 50mW per facet but also have shown an ultra low relative intensity noise (RIN) of -162 dB/Hz ± 1.6 dB/Hz in 0.1-13 GHz range for the first year. At the end of the project we have succeeded in obtaining a very low RIN of -160 dB/Hz ± 2 dB/Hz over a wide bandwidth from 50 MHz to 18 GHz.
This paper deals with the analysis of the experimental results, obtained with quantum dash Fabry Perot lasers, especially those relating to noise performances and also the first results of reliability demonstrating the suitability of these new devices for microwave optical links.
At the present time, due to their improved spectral characteristics accompanied by low noise and high linearity of current-light output power features, 1.55 μm DFB lasers are key components of analog microwave fibre optical links. These devices are the most frequently used as both the optical source and RF/optical modulator. Especially in the case of direct intensity modulation links, stringent requirements repose on these devices together in terms of performances and reliability, the latter being a crucial issue for the viability of the optical links. This paper deals with the investigation on the reliability of 1.55 μm strained quantum well ridge DFB lasers. Long term ageing tests were performed during 12,000 hours at 80°C ambient temperature and a constant bias current of 140 mA corresponding to 10 mW output power. These tests ended, none failure or decrease of the optical power was observed.
A detailed evaluation based on crucial parameters for direct microwave modulation as static characteristics, emission spectra and relative intensity noise (RIN) has revealed only negligible changes after ageing.
The explosion of internet traffic, the increase in data or multimedia transmission are the main reasons for a huge rise in demand for transmission bandwidth especially in dense wavelength division multiplexing (DWDM) systems. Nowadays this technique must be developed in the 1.4 μm to 1.65 μm wavelength range to follow the progress of new low-loss fibres. A decade ago, a new class of gain material, based on quantum dot was intensively studied. For three years, researchers have succeeded in growing new elongated nano-structures based on InP, called quantum dashes, for applications beyond the wavelength limit of 1.3 μm using GaAs-based quantum dots. These great strides in the elaboration of these new gain materials could meet this gain bandwidth. In the framework of the European project, BIGBAND, we have developed 1.55 μm quantum dash Fabry-Perot lasers based on InP using a ridge waveguide operating in continuous wave at room temperature. These devices have reached the power of 40 and 50mW per facet in p side up and down configurations respectively and have shown a low relative intensity noise (RIN) of -162 dB/Hz ± 1.6 dB in 0.1-13 GHz range.
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