P. Resneau

Coherence function control of Quantum Dot Superluminescent Light Emitting Diodes by frequency selective optical feedback.

Low coherent light interferometry requires broad bandwidth light sources to achieve high axial resolution. Here, Superluminescent Light Emitting Diodes (SLDs) utilizing Quantum Dot (QD) gain materials are promising devices as they unify large spectral bandwidths with sufficient power at desired emission wavelengths. However, frequently a dip occurs in the optical spectrum that translates into high side lobes in the coherence function thereby reducing axial resolution and image quality. We apply the experimental technique of frequency selective feedback to shape the optical spectrum of the QD-SLD, hence optimizing the coherence properties. For well-selected feedback parameters, a strong reduction of the parasitic side lobes by a factor of 3.5 was achieved accompanied by a power increase of 40% and an improvement of 10% in the coherence length. The experimental results are in excellent agreement with simulations that even indicate potential for further optimizations.

High power, very low noise and long term ageing 1.55 /spl mu/m InP-based Fabry-Perot quantum dash lasers under CW operation

Under continuous wave operation at room temperature, 50 mW per facet output power, -162 dB/Hz wide spectrum relative intensity noise and 6500 hours accelerated ageing with no failure of quantum dash Fabry-Perot lasers are presented.

Intensity noise of ultrabroadband quantum dot light emitting diodes and lasers at 1.3 μm

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 SLEDs, and shows strong deviation from the Excess Noise character above threshold.

High-power and low-noise 1.55 μm InP-based quantum dash lasers

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.

Long-term aging with highly stable performances of 1.55-μm DFB lasers 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.

High-power, high-reliability, and narrow linewidth, Al-free DFB laser diode for Cs pumping (852nm)

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).

High Power, Very Low Noise, C.W. Operation of 1.32μm Quantum-Dot Fabry-Perot Laser Diodes

1.32 mum InAs quantum dot narrow ridge lasers have reached a record single spatial mode optical power of 130 mW/facet under CW operation. Furthermore we demonstrate a very low relative intensity noise of -159 dB/Hz plusmn2 dB/Hz in the 0.1-10 GHz range

High power and very low noise operation at 1.3 and 1.5 μm with quantum dot and quantum dash Fabry-Perot lasers for microwave links

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.

Mode locking and bandwidth enhancement in single section ridge laser with two spatial modes.

With a single section ridge multi-quantum well laser diode having two spatial modes, we demonstrate mode locking and modulation bandwidth enhancement at 1580nm.

High-power high-reliability narrow-linewidth Al-free DFB laser diode for Cs pumping (852 nm)

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.