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 present measurements of the linewidth enhancement factor of a distributed feedback quantum cascade laser (DFB-QCL) using the so-called self-mixing technique. The linewidth enhancement factor is investigated by analyzing optical feedback induced changes of the emission properties of the laser. We will demonstrate that our self-mixing setup works well with QCLs in the mid infrared wavelength regime, and that it is possible to use the obtained signal to extract the linewidth enhancement factor. We present a setup that records the self-mixing signal with the voltage signal across the laser device using the laser as a detector itself. In this contribution we will show the advantages of this measurement technique. First measurements of the linewidth enhancement factor yield values that rise from 0.24 to 2.6 with an increase of the injection current of the QCL. We will discuss the influence of the injection current on the linewidth enhancement factor.
We investigate the performance of a modern hollow-core optical fibre coupled to a GaAs-based quantum cascade laser (QCL) emitting at a wavelength of 10.7 μm. The QCL is operated in pulsed operation with current pulses of 100 ns width at a repetition rate of 10 kHz at a heat sink temperature of 258 K. The emitted light is collected by a f/1.6 ellipsoidal mirror and focused onto the hollow-core optical fibre. The investigated fibre is 2 m long and is designed for a transmission wavelength of 10.6 μm. After the transmission through fibre, the light is collected by a ZnSe-aspheric lens. We investigate the transmission efficiency of the hollow-core optical fibre and its influence on the intensity noise properties by measuring the transmitted optical peak power in relation to the emitted optical peak power. We find a total transmission loss of 6.25 dB. We then analyze the influence of this hollow-core optical fibre on the intensity noise properties of the QCL in terms of the relative intensity noise (RIN). We find that for the same detected optical peak powers the RIN of the optical power transmitted through the fibre is about 4 dB/Hz lower than the RIN of the emitted optical power. We attribute this reduction of the RIN level to a random selection process of photons due to the losses of the fibre which alters the intensity noise towards the standard quantum limit.
We present results of comprehensive investigations of the
intensity noise of continuous wave (CW) operated quantum cascade
lasers (QCLs) under various operation conditions. These
experiments are performed with the aim to measure and understand
the intensity noise of QCLs, and furthermore to explore the
potential to generate non-classical light, i.e. squeezed states of
light with sub-shot intensity noise with these new devices. First,
we measure the relative intensity noise (RIN) and find that the
relative intensity noise behaviour of QCLs is different from that
of bipolar edge emitting lasers and Vertical-Cavity Surface-Emitting Laser (VCSELs). These observations are explained by a semi-classical noise description in which the particular level scheme of the QCLs is incorporated via an effective cascaded three-level model. Second, we compare this intensity noise with respect to the shot-noise level in order to explore the possibility of generation of squeezed states of light in the mid-infrared spectral domain with QCLs. In our first experiments we find only an intensity noise 2 dB above the shot noise level. Finally, these experimental results, the possible origin of the observed non-successful sub-shot noise generation, as well as possibilities for future trends, applications and the limitations of these non-classical states of light with respect to sensing and spectroscopic applications are discussed.