Quantum Dot Superluminescent Diodes Research Articles

Silent white light: Reduction of the second-order intensity correlation coefficient

We investigate the intrawaveguide statistics manipulation of broadband light by combining semiconductor quantum dot physics with quantum optics. By cooling a quantum dot superluminescent diode to the liquid nitrogen temperature of 77 K, Blazek [] have demonstrated a temperature-dependent reduction of the second-order intensity correlation coefficient from 2 for thermal amplified spontaneous emission light to g(2)(0,T=190K)≈1.33. Here, we model the broadband photon statistics assuming amplified spontaneous emission radiation in a pumped, saturable quantum dot gain medium. We demonstrate that, by an intensity increase due to the quantum dot occupation dynamics via the temperature-tuned quasi-Fermi levels, together with the saturation nonlinearity, a statistics manipulation from thermal Bose-Einstein statistics towards Poissonian statistics can be realized, thus producing “silent white light” with a reduced second-order correlation coefficient. Such intensity-noise-reduced broadband radiation is relevant for many applications such as optical coherence tomography, optical communication, or optical tweezers. Published by the American Physical Society 2024

Broadband chirped InAs quantum-dot superluminescent diodes with a small spectral dip of 0.2 dB

We report on the fabrication and characterization of InAs/GaAs chirped multilayer quantum-dot superluminescent diodes (CMQD-SLDs) with and without direct Si doping in QDs. It was found that both the output power and the spectral width of the CMQD-SLDs were significantly enhanced by direct Si doping in the QDs. The output power and spectral width have been increased by approximately 18.3% and 40%, respectively. Moreover, we shortened the cavity length of the doped CMQD-SLD and obtained a spectral width of 106 nm. In addition, the maximum output power and spectral width of the CMQD-SLD doped directly with Si can be further increased to 16.6 mW and 114 nm, respectively, through anti-reflection coating and device packaging. The device exhibited the smallest spectral dip of 0.2 dB when the spectrum was widest. The improved performances of the doped CMQD-SLD can be attributed to the direct doping of Si in the QDs, optimization of device structure and device packaging.

Stochastic Simulation of Emission Spectra and Classical Photon Statistics of Quantum Dot Superluminescent Diodes

We present a stochastic procedure to investigate the correlation spectra of quantum dot superluminescent diodes. The classical electric field of a diode is formed by a polychromatic superposition of many independent stochastic oscillators. Assuming fields with individual carrier frequencies, Lorentzian linewidths and amplitudes we can form any relevant experimental spectrum using a least square fit. This is illustrated for Gaussian and Lorentzian spectra, Voigt profiles and box shapes. Eventually, the procedure is applied to an experimental spectrum of a quantum dot superluminescent diode which determines the first- and second-order temporal correlation functions of the emission. We find good agreement with the experimental data and a quantized treatment. Thus, a stochastic field represents broadband light emitted by quantum dot superluminescent diodes.

Electrically pumped continuous-wave O-band quantum-dot superluminescent diode on silicon.

High-power, broadband quantum-dot (QD) superluminescent diodes (SLDs) are ideal light sources for optical coherence tomography (OCT) imaging systems but have previously mainly been fabricated on native GaAs- or InP-based substrates. Recently, significant progress has been made to emigrate QD SLDs from native substrates to silicon substrates. Here, we demonstrate electrically pumped continuous-wave InAs QD SLDs monolithically grown on silicon substrates with significantly improved performance thanks to the achievement of a low density of defects in the III-V epilayers. The fabricated narrow-ridge-waveguide device exhibits a maximum 3 dB bandwidth of 103 nm emission spectrum centered at the O-band together with a maximum single facet output power of 3.8 mW at room temperature. The silicon-based SLD has been assessed for application in an OCT system. Under optimized conditions, a predicted axial resolution of ∼5.3µm is achieved with a corresponding output power of 0.66 mW/facet.

Enhanced performance of InAs/GaAs quantum dot superluminescent diodes by direct Si-doping

It is necessary to improve the output power and spectral width of superluminescent diodes (SLDs) simultaneously. In this paper, we show that both the output power and the spectral width of the SLDs based on InAs/GaAs quantum dots (QDs) can be significantly enhanced by direct Si-doping in the QDs. The maximum output power of the Si-doped QD-SLD reaches 20.5 mW at an injection current of 570 mA, while that of the undoped one with an identical structure is only 17.8 mW at the injection current of 550 mA. Moreover, the broadest spectral width of the doped QD-SLD is 105 nm, while that of the undoped QD-SLD is 93 nm. The enhanced performance of the doped QD-SLDs can be attributed to the direct Si doping that leads to inactivating the nonradiative recombination centers within or near the QDs and provides excess carriers to occupy the higher excited states.

Wide and tunable spectral asymmetry between narrow and wide facet outputs in a tapered quantum-dot superluminescent diode.

A wide spectral asymmetry between the front and rear facets of a tapered chirped quantum dot multi-section superluminescent diode is reported. The spectral asymmetry between the two facet outputs was found to be tunable and highly dependent on the bias asymmetry between the two contact sections, with a spectral mismatch of up to 14 nm. Numerical simulations confirmed a relationship between this spectral asymmetry and the non-uniform filling of the quantum dots' confined states when different current densities are applied to the device electrodes. The results from this investigation open up an additional degree of freedom for multi-section superluminescent diodes, which could pave the way for optical bandwidth engineering via multiplexing the spectral output from both facets, using only a single device.

Emission spectrum of broadband quantum dot superluminescent diodes

We present a microscopic theory of the amplified spontaneous emission of a spectrally broadband quantum dot superluminescent diode with tilted end facets within the quantum white noise limit. From this multimode quantum theory, we have the ability to obtain all orders of temporal correlation functions. In particular, we derive rate equations for the optical power densities, the level occupation of inhomogeneous ensemble of quantum dots within the diode, as well as the emitted optical spectra. As the main result, we find the external power spectrum as a convolution of the intra-diode photon spectrum with a Lorentzian response. Assuming a Gaussian light-matter coupling results in a similar shaped Gaussian output spectrum, which agrees very well with available experimental data.

High-power quantum-dot superluminescent tapered diode under CW operation.

A high-power quantum-dot superluminescent diode is demonstrated under continuous-wave operation, with an output power of 137.5 mW and a corresponding spectral bandwidth of 21 nm. This represents not only the highest output power, but also a record-high power spectral density of 6.5 mW/nm for a CW-operated superluminescent diode in the 1.1 - 1.3 μm spectral region, marking more than a 6-fold increase with respect to the state of the art. The two-section contact layout of the reported device introduces additional degrees of freedom, which enable a wide tunability of the bandwidth and power depending on the desired application. A maximum bandwidth of 79 nm was recorded, with an output power of 1.4 mW. The high-power continuous-wave operation of this device would be particularly relevant for continuous, high-speed, high-sensitivity spectroscopy, imaging and sensing applications, as well as in optical communications.

Effects of Modulation P-Doping on Thermal Stability of InAs/GaAs Quantum Dot Superluminescent Diodes

Effects of Modulation P-Doping on Thermal Stability of InAs/GaAs Quantum Dot Superluminescent Diodes

Broadband Chirped InAs Quantum-Dot Superluminescent Light-Emitting Diodes With InxAl1-xAs Strain-Reducing Layers

In this paper, broadband InAs quantum-dot (QD) superluminescent light-emitting diodes (SLEDs) are grown by molecular beam epitaxy, fabricated, and then characterized. In order to achieve broadband and uniform emission spectra, the active regions contain a combination of chirped InAs QDs with different InxAl1-xAs strain-reducing layers (SRLs). It has been shown that the InxAl1-xAs SRLs can effectively enlarge the QD emission energy separation between the ground and the excited states. In this paper, QDs with increased energy separation are utilized to enable a broadband QD ensemble by adding additional QD layers with the ground state emission wavelength tuned to fill the gap in emission. In addition, we employed a short postgrowth annealing process of 30 s to further even out the emission spectra. Characterizations of the emission spectra of the as-grown QDs and fabricated QD SLEDs are performed by room-temperature photoluminescence and electroluminescence under continuous-wave (c-w) operation, respectively. In the SLED devices, a broad and uniform spectrum with a linewidth of 100 nm at 3 dB is realized at an injection current level of 100 mA, and no significant spectrum dip is observed in the entire injection current window ranging from 50 $\mu\text{A}$ to 100 mA.

Active multi-mode-interferometer broadband superluminescent diodes**Project supported by the National Natural Science Foundation of China (No. 61274072) and the National High Technology Research and Development Program of China (No. 2013AA014201).

We report a new quantum dot superluminescent diode with a new device structure. In this device, a multi-mode-interferometer configuration and a J-bend structure were monolithically integrated. Owing to the multi-mode-interferometer structure, the superluminescent diode exhibits 60% increase in output power and 43% reduction in the differential resistance compared with the uniform waveguide width superluminescent diode fabricated from the same wafer. Our device produces an emission spectrum as wide as 103.7 nm with an output power of 2.5 mW at 600 mA continue-wave injection current. This broadband emission spectrum makes the axial resolution of the optical coherence tomography system employing the superluminescent diode to 6 μm in theory, which is high enough for most tissue imaging.

大功率短波长InAlGaAs/AlGaAs量子点超辐射发光管

大功率短波长InAlGaAs/AlGaAs量子点超辐射发光管

Broadband and high-speed swept external-cavity laser using a quantum-dot superluminescent diode as gain device**Project supported by the National Natural Science Foundation of China (Grant No. 61274072) and the National High Technology Research and Development Program of China (Grant No. 2013AA014201).

A wide wavelength tuning range swept external-cavity laser using an InAs/GaAs quantum-dot superluminescent diode as a gain device is demonstrated. The tunable filter consists of a polygon scanner and a grating in Littrow telescope-less configuration. The swept laser generates greater than 54-mW peak output power and up to 33-kHz sweep rate with a sweep range of 150 nm centered at 1155 nm. The effects of injection current and sweep rate on the sweep performance of the swept laser are studied.

Tailored quantum statistics from broadband states of light

We analyze the statistics of photons originating from amplified spontaneous emission generated by a quantum dot superluminescent diode. Experimentally detectable emission properties are taken into account by parametrizing the corresponding quantum state as a multimode phase-randomized Gaussian density operator. The validity of this model is proven in two subsequent experiments using fast two-photon-absorption detection observing second-order equal-time and second-order fully time-resolved intensity correlations on femtosecond timescales. In the first experiment, we study the photon statistics when the number of contributing longitudinal modes is systematically reduced by applying well-controlled optical feedback. In a second experiment, we add coherent light from a single-mode laser diode to quantum dot superluminescent diode broadband radiation. Tuning the power ratio, we realize tailored second-order correlations ranging from Gaussian to Poissonian statistics. Both experiments are very well matched by theory, thus giving first insights into the quantum properties of radiation from quantum dot superluminescent diodes.

InAs/GaAs quantum-dot superluminescent diodes monolithically grown on a Ge substrate.

We report the first InAs/GaAs quantum-dot (QD) superluminescent diode (SLD) monolithically grown on a Ge substrate by molecular beam epitaxy. The QD SLD exhibits a 3 dB emission bandwidth of ~60 nm centered at 1252 nm with output power of 27 mW at room temperature. The 3 dB bandwidth is very stable over the temperature range from 20 °C to 100 °C, which highlights the potential for integration with high performance ICs.

Tailored first- and second-order coherence properties of quantum dot superluminescent diodes via optical feedback

We demonstrate experimentally that the first- and second-order coherence properties of light emitted by a quantum dot superluminescent diode can be simultaneously tailored by well-controlled optical feedback. Depending on feedback intensity and feedback spectral range we achieve a spectral width Δλ between 120 and 0.26 nm, corresponding to a coherence length in first order in the range between 13 and 5820 μm, while the central second-order coherence degree g((2))(τ=0) is tuned gradually from a thermal value of g((2))(0)~1.8 down to the coherent laser limit of g((2))(0)=1.0. These results are complemented by comprehensive investigations of relative intensity noise, which are in excellent agreement with the observed intensity correlation behavior.

Emission State Hierarchy Governed Coherence and Intensity Noise Properties of Quantum Dot Superluminescent Diodes

There is an inherent link between the coherence properties in the first and second order, depending on the quantum optical characteristics of the light emitting source. Whereas the coherence in the first order reflects the spectral distribution of radiation, the coherence in the second order describes the intensity fluctuations of photonic beams quantified by the relative intensity noise. In this paper, we demonstrate how the particularly interesting and highly complex spectral emission state hierarchy of a quasi-zero-dimensional inhomogeneously broadened quantum dot superluminescent diode governs both the coherence and intensity noise properties. We confirm that indeed a generalized Hodara formula reflecting the pure thermal emission character of the investigated quantum dot superluminescent diode quantitatively explains the experimentally observed complex intensity noise behavior just by the observed complex spectral behavior.

High-power InAs quantum-dot superluminescent diodes with offset J-shaped waveguides

We demonstrate a superluminescent diode (SLD) that uses an offset between straight and bent regions in a J-shaped ridge waveguide. The output power is improved several times with respect to similar J-shaped SLDs without the offset. We obtain a high, continuous output power of 31 mW and wide spectral bandwidths up to 90 nm centered at about 1.1 µm.

The Effect of Double-Pass Gain on the Performances of a Quantum-Dot Superluminescent Diode Integrated With a Semiconductor Optical Amplifier

We fabricate a quantum-dot (QD) superlumenescent diode (SLD) integrated with a semiconductor optical amplifier (SOA). The integrated device exhibits coordinative working between the SLD and SOA when the two sections are pumped with a series of different currents. However, the SLD source affects the device behavior not via the amount of energy supplied by itself, but via an existing double-pass gain throughout the whole structure. With the help of a QD device model, this behavior is numerically analyzed which explains the origin of competition between different QD states in the emission spectra as well as the strong power-control capability of the SLD source.

Improved Continuous-Wave Performance of Two-Section Quantum-Dot Superluminescent Diodes by Using Epi-Down Mounting Process

Using AlN submounts with metal patterns made by a photolithographic process, the two-section quantum-dot superluminescent diodes were mounted epi-down on the heatsinks. It is demonstrated that the epi-down mounting process can offer improved heat dissipation and optical performance in the two-section devices. Under continuous-wave operation without temperature control, by properly controlling the pump levels in the two sections, a broad flat-top-like emission spectrum of 112 nm with a high output power of 107 mW is obtained from a two-section quantum-dot superluminescent diode with an epi-down mounting structure.