Multiquantum-well Lasers Research Articles

Watt-level continuous-wave antimonide laser diodes with high carrier-confined active region above 2.5 µm

Thanks to high performance above room temperature, antimonide laser diodes have shown great potential for broad application in the mid-infrared spectral region. However, the laser`s performance noticeably deteriorates due to the reduction of carrier confinement with increased emission wavelength. In this paper, a novel active region with higher carrier confinements both of electron and hole, by the usage of an indirect bandgap material of Al0.5GaAs0.04Sb as the quantum barrier, was put up to address the poor carrier confinement of GaSb-based type-I multi-quantum-well (MQW) diode lasers emission wavelength above 2.5 µm. The carrier confinement and the differential gain in the designed active region are enhanced as a result of the first proposed usage of an indirect-gap semiconductor as the quantum barrier with larger band offsets in conduction and valence bands, leading to high internal quantum efficiency and low threshold current density of our lasers. More importantly, the watt-level output optical power is obtained at a low injection current compared to the state of the art. Our work demonstrates a direct and cost-effective solution to address the poor carrier confinement of the GaSb-based MQW lasers, thereby achieving high-power mid-infrared lasers.

Designing a 1550 nm Pulsed Semiconductor Laser-Emission Module Based on a Multiquantum-Well Equivalent Circuit Model

The demand for eye-safe 1550 nm pulsed semiconductor laser-emission modules is increasing in the field of active laser detection, owing to their long range and high precision. The high power and narrow pulse of these modules can significantly improve the distance and accuracy of active-laser detection. Here, we propose an equivalent circuit model of a multiquantum-well laser based on the structure of a laser device. We developed a design method for 1550 nm pulsed semiconductor laser-emission modules according to the equivalent circuit model of an InGaAlAs laser. In this method, the module design was divided into laser chip and laser-driver levels for optimization and simulation. At the chip level, a high-output power laser chip with optimal cavity length and optical facet coating coefficients was obtained. At the laser-driver level, the model was applied to a drive circuit to provide direct narrow optical pulses. Finally, a laser-emission module was fabricated based on the optimal design results. In addition to the power-current features of the actual laser, the critical voltage of the emission module and laser pulses were tested. By comparing the test and simulation results, the effectiveness of the proposed method was confirmed.

Design of Monolithic 2D Optical Phased Arrays Heterogeneously Integrated with On-Chip Laser Arrays Based on SOI Photonic Platform.

In this work, heterogeneous integration of both two-dimensional (2D) optical phased arrays (OPAs) and on-chip laser arrays based on a silicon photonic platform is proposed. The tunable multi-quantum-well (MQW) laser arrays, active switching/shifting arrays, and grating antenna arrays are used in the OPA module to realize 2D spatial beam scanning. The 2D OPA chip is composed of four main parts: (1) tunable MQW laser array emitting light signals in the range of 1480-1600 nm wavelengths; (2) electro-optic (EO) switch array for selecting the desired signal light from the on-chip laser array; (3) EO phase-shifter array for holding a fixed phase difference for the uniform amplitude of specific optical signal; and (4) Bragg waveguide grating antenna array for controlling beamforming. By optimizing the overall performances of the 2D OPA chip, a large steering range of 88.4° × 18° is realized by tuning both the phase and the wavelength for each antenna. In contrast to the traditional thermo-optic LIDAR chip with an external light source, the overall footprint of the 2D OPA chip can be limited to 8 mm × 3 mm, and the modulation rate can be 2.5 ps. The ultra-compact 2D OPA assembling with on-chip tunable laser arrays using hybrid integration could result in the application of a high-density, high-speed, and high-precision lidar system in the future.

Theoretical investigation of nitride nanowire-based quantum-shell lasers

We executed a feasibility study of a novel laser structure composed of GaN nanowire (NW) and GaInN/GaN multi-quantum-shell (MQS) active layers. We predicted that the novel structure would increase of the optical confinement factor Γ because of its three-dimensional active layers. We analyzed the optical field distribution of the waveguide in the structure by the effective refractive index method, and the optical confinement factor was calculated. When the active layers had five periods of 4 nm-thick well layers and 9 nm-thick barrier layers, the confinement factor was estimated to be 6.5%. This is more than three times higher than that of a conventional planar multi-quantum-well (MQW) structure. The threshold current density estimated from the gain curve was shown to be 44% lower than that of a conventional MQW laser.

Performance of Widely Tunable Multi-Quantum-Well and Bulk Laser Diodes and the Main Limiting Factors

The output power and tuning performance of multi-quantum-well (MQW) and bulk InGaAsP/InP-distributed Bragg reflector (DBR) tunable laser diodes (TLDs) are investigated over a wide wavelength tuning range using physics-based PICS3D and VPI laser simulation tools within the travelling-wave formalism. The key result of our simulations is the discovery of a new effect in TLDs due to intervalence band absorption (IVBA) in passive phase and DBR sections, which limits the wavelength tuning range. The physical mechanism responsible for such a behavior is a collapse of the spectral-mode selectivity by the DBR due to large IVBA losses in the phase or/and DBR sections. We fundamentally demonstrate different roles played by the IVBA in the active and passive sections of a TLD. It is shown that the IVBA in passive sections and the carrier relaxation broadening (CRB) of the Lorentzian lineshape function in the lasers’ active and passive sections play a crucial role in TLD tuning operation. The IVBA coefficient $\text{k}_{\mathrm {IVBA}}$ and the intraband relaxation time $\tau _{in}$ are the major limiting factors that define the output power variation and the achievable tuning range of the lasers. Both bulk and MQW lasers with small $\text{k}_{\mathrm {IVBA}}$ demonstrate a wide wavelength tuning range above 30 nm, while for large $\text{k}_{\mathrm {IVBA}}$ , the tuning range drops below 10 nm. We show that the output power variation with tuning due to the CRB parameter $\tau _{in}$ is qualitatively different in bulk and MQW TLDs. The TLD tuning and power performance is also strongly affected by the shapes of the net gain and the cavity mirror loss spectra and their mutual positioning with respect to the lasing cavity mode during the tuning. The limiting parameters $\text{k}_{\mathrm {IVBA}}$ and $\tau _{in}$ as well as gain and mirror loss spectra must be thoroughly evaluated in each TLD structure prior to the device design and optimization in order to achieve the best performance in terms of the wavelength tuning and the output power stability.

Effect of QW thickness and numbers on performance characteristics of deep violet InGaN MQW lasers

The performance characteristics of deep violet indium gallium nitride (InGaN) multiquantum well (MQW) laser diodes (LDs) with an emission wavelength of around 390 nm have been investigated using the integrated system engineering technical computer aided design (ISE-TCAD) software. A comparative study on the effect of quantum well (QW) thickness and number on electrical and optical performance of deep violet In 0.082 Ga 0.918 N/GaN MQW LDs have been carried out. The simulation results showed that the highest slope efficiency and external differential quantum efficiency (DQE), as well as the lowest threshold current are obtained when the number of wells is two. The different QW thickness values of 2.2, 2.5, 2.8, 3 and 3.2 nm were compared and the best results were achieved for 2.5 nm QW thickness. The radiative recombination rate decreases with increasing QW thickness because of decreasing electron and hole carrier densities in wells. By increasing QW thickness, output power decreases and threshold current increases.

Optically pumped lasing properties of InGaN/GaN stripe multiquantum wells with ridge cavity structure on patterned (001) Si substrates

We demonstrated lasing action and investigated the optical properties of multiquantum-well (MQW) stripe crystals on patterned (001) Si substrates. Longitudinal and higher order transverse modes were observed from a ridge waveguide structure. These results strongly suggest the possibility of fabricating InGaN MQW laser diodes on (001) Si.

Characterization of 60 GHz Multi Quantum well passively mode-locked laser under optical self-injection locking

The quality and pulse compression of the 60GHz millimeter wave signals generated by 750μm long InAlGaAs Multi Quantum Well (MQW) passively mode locked laser under free running and optical self-injection locked conditions are experimentally characterized in terms of longitudinal modes under certain bias currents that range from 24mA to 90mA. Initially, the MQW laser is characterized in free running condition with no external injection. The measurements reflect that the free spectral range of laser under test is around 61GHz and exhibit more than 22 lasing modes. The laser is then integrated into low phase noise self-injection locking oscillator by feeding a part of output RF signal back into the laser cavity to enhance passive mode locking. By doing so the microwave line width of our laser is reduced from 900kHz to 24kHz with significant increase in output of resultant beat tones which exhibits strong passive mode locking. This is the first time that the free running microwave line width of MQW laser is reduced up to this level. It is evident from our experimental investigation that as we increase the power and phase correlation between different longitudinal modes inside laser cavity through optical self-injection, the strength of the passively mode locked mechanism is significantly increased and the phase noise of radio frequency signal is drastically reduced.

Characterization of 60 GHz multi quantum well passively mode-locked laser under optical self injection locking

The quality and pulse compression of the 60GHz millimeter wave signals generated by 750μm long InAlGaAs Multi Quantum Well (MQW) passively mode locked laser under free running and optical self injection locked conditions are experimentally characterized in terms of longitudinal modes under certain bias currents that range from 24mA to 90mA. Initially, the MQW laser is characterized in free running condition with no external injection. The measurements reflect that the free spectral range of laser under test is around 61GHz and exhibit more than 22 lasing modes. The laser is then integrated into low phase noise self injection locking oscillator by feeding a part of output RF signal back into the laser cavity to enhance passive mode locking. By doing so the microwave line width of our laser is reduced from 900kHz to 24kHz with significant increase in output of resultant beat tones which exhibits strong passive mode locking. This is the first time that the free running microwave line width of MQW laser is reduced up to this level. It is evident from our experimental investigation that as we increase the power and phase correlation between different longitudinal modes inside laser cavity through optical self injection, the strength of the passively mode locked mechanism is significantly increased and the phase noise of radio frequency signal is drastically reduced.

Characteristic Optimization of 1.3 μm High-Speed MQW InGaAsP-AlGaInAs Lasers

We investigate 1.3 μm multi quantum-well (MQW) lasers with InGaAsP (well) and InGaAlAs (barrier) on InP for high speed application, compared to the typical structures of InGaAsP (well)-InGaAsP (barrier)/InP and InGaAlAs (well)-InGaAlAs (barrier)/InP with the same quaternary in the well and barrier. We calculate the characteristics of band offset and gain of InGaAsP-AlGaInAs quantum wells (QWs). The advances of the new QW design are mainly rooted in the large ratio between conduction-band and valence-band offsets (ΔEc:ΔEv = 7:1), higher than the typical value of 4:6 in InGaAsP-InGaAsP and 7:3 in InGaAlAs-InGaAlAs for 1.3 μm lasers. Due to the low confinement energy of holes, non-uniformity of carrier distribution over multi-InGaAsP-AlGaInAs QWs is significantly reduced. The enhancement of high-speed performance of InGaAsP-AlGaInAs MQW lasers is investigated in terms of turn-on oscillation.

Long-Term Degradation Behavior of 2.3-$\mu\hbox{m}$ Wavelength Highly Strained InAs/InP MQW-DFB Lasers With a p-/n-InP Buried Heterostructure

We investigate the long-term degradation of 2.3-μm wavelength InAs/InP highly strained multiquantum-well distributed-feedback lasers with a p- and n-type InP buried heterostructure during constant power aging. Stable operation beyond 20 000 h is confirmed at an ambient temperature of 45 °C and with a constant output power of 3 mW, and we successfully fabricate a practical optical source for trace gas monitoring applications. A conventional diffusion process dominates the main degradation mechanism as found with conventional telecommunication lasers. Furthermore, we show that some defects are located in the regrown p-type InP layer above the active layer and that downward diffused defects degrade the guide, upper separate confinement heterostructure (SCH), and active layers.

Mode pattern dependence on the eccentricity of microstadium resonators

Microdisk and microstadium resonators based on InGaAsP multiquantum-well laser structures were fabricated by focused ion beam employing Ga+ ion milling and polishing followed by selective chemical etching. Stadia with very good morphology and with different eccentricities were fabricated for the study of optical mode selection. Light emission was investigated by infrared microscopy and spectroscopy. The measured emission pattern and the spectra agree well with a simple model based on the summation over periodic orbits or scar modes. The dependence of the scar mode emission with the resonator eccentricity was modeled based on the difference between photon lifetime and orbital round-trip time. The mode selection dependence with the surrounding index of refraction is suggested for chemical sensing applications.

50th anniversary of the laser

On July, 7, 1960 a press conference at Huyghes announced that Maiman had assembled and put into operation the first laser. It was the very pulsed ruby laser that everybody knows today. The announcement came as a bomb. Nobody expected that in an unknown laboratory, new to the race to build a laser, this result could be obtained. It was such an unexpected result that many still today mantain that the true laser was discovered at Bell by Shawlow. This result was achieved through a long story which passed by the Townes maser and many tentative experiments and discussions both in the USA and Soviet Union. In this special issue we present a collection of papers which provide further information as to what happened after Einstein introduced the concept of stimulated emission. The first paper is a short paper by Townes on the development of the physics of microwaves following the creation of the maser. When the laser came on the stage one of its properties was the inherent coherence of the emitted light. Emil Wolf’s contribution enlights the early days of coherence to which he so much contributed and the very timely first Rochester Conference which was held on June 27-29, 1960 a few days before the Times announcement of the Maiman achievement. Important contributions were given by Soviet Scientists and, Svetlana Lukishova’s contributions helps us understand the work of Valentin Fabrikant which was mostly unknown to western scientists. At the end of his life, Maiman went to Vancouver in Canada and Andrew H. Rawicz gives his testimoniancy of his friendship there. Coherence and the statistical properties of laser light were much studied and we have two exceptional papers by Roy Pike and Jan Perina discussing these arguments. The issue also contains three more papers presenting some earlier achievements in the construction of multiquantumwell laser (M. L. Dotor, P. Huertas, P. A. Postigo, D. Golmayo and F. Briones), the first measurements on very short pulses (H. P. Weber and R. Dandliker) and spatial coherence (D. P. Barato and M. L. Calvo).

Control of chaos in an external-cavity multi-quantumwell laser subjected to dual-wedges and optical dual-feedback

A multi-parameter chaos-control method used to control chaos in an external cavity multi-quantum-well (MQW) laser via the dual-wedges and external delayed optical dual-feedback is presented. The physical model of the laser dynamic is established under the conditions of the dual-wedges and dual-feedback light control. The frequency detuning and stable ranges of the control system are theoretically demonstrated. The optical-length of the feedback light may be adjusted by shifting horizontally or sliding the dual-wedges relatively in the external optical road, which will alter the delaying time and feedback intensity of the dual-feedback light. Accordingly, the multi-parameter chaos-control of the optical dual-feedback may be achieved physically. The numerical simulations approve that the chaotic laser may be controlled into a stable state, a single-periodic state and multi-periodic states, and the controlled periodic pulse power may be increased.

Simultaneous sudden changes of electrical behavior at the threshold in laser diodes

Precise ac electrical measurements as well as dc I-V plots at forward bias have been used to characterize multi-quantum-well (MQW) laser diodes. Step offsets of apparent conductance, apparent capacitance, junction voltage, series resistance, and ideality factor at lasing threshold were observed. To compare the electrical characteristics of different diodes numerical simulations of the IdV∕dI-I curve of the double-heterostructure (DH) laser were performed. We find that the conventional model used to explain this curve is not very satisfactory. Our simulations demonstrate that the junction voltage, series resistance, and ideality factor for both DH and MQW lasers exhibit the same sudden changes at threshold. Perhaps the electrical behavior near threshold for all laser diodes is very similar.

Sudden Change of Electrical Characteristics at Lasing Threshold of a Semiconductor Laser

Accurate forward electrical characteristics of multiquantum-well (MQW) lasers have been measured using ac admittance measurements together with dc I-V plot. The synchronous step offsets of apparent conductance, apparent capacitance, junction voltage, series resistance, and ideality factor at the onset of lasing were observed for the first time. With this effect, the lasing threshold can be deduced immediately by the LCR Meter. It is also found that the junction voltage jumps abruptly to a saturated value at the onset of lasing, and the starting and end points of jumping exactly correspond to the maximum of the second derivative of lasing power with respect to current and the kink point of the first derivative, respectively. All of the phenomena may help to verify and improve existing semiconductor laser models. In addition, negative capacitance effect in LDs was observed

Study on high-temperature performances of 1.3-/spl mu/m InGaAsP-InP strained multiquantum-well buried-heterostructure lasers

Stripe-width and cavity length dependencies of high-temperature performances of 1.3-/spl mu/m InGaAsP-InP well-designed buried-heterostructure strained multiquantum-well (MQW) lasers were investigated. The threshold currents as low as 4.5/10.5 mA and slope efficiencies as high as 0.48/0.42 mW/mA at 25/spl deg/C/85/spl deg/C were obtained in the MQW lasers with 1.5-/spl mu/m width, 250-/spl mu/m length, and 0.3/0.85 facet reflectivity. With temperature increasing from 25/spl deg/C to 85/spl deg/C, the MQW lasers exhibited lower output power degradation, the minimum value was 1.78 dB at an operation current of 45 mA. The MQW lasers were suitable for application in optical access networks.

Study on InGaAsP–InGaAs MQW-LD With Symmetric and Asymmetric Separate Confinement Heterostructure

We studied symmetric and asymmetric InGaAsP-InGaAs 1.55-/spl mu/m multiquantum-well (MQW) laser diodes (LDs) with highly p-doped layers in the two-step separate confinement heterostructure (SCH). The p-doping in p-SCH suppresses the electron overflow from the MQWs to p-SCH, but it is an origin of free carrier absorption loss. An additional InGaAsP layer inserted inside n-SCH makes asymmetric field distribution and, therefore, reduces the portion of optical field distribution in highly p-doped regions with high optical loss. Compared with symmetric structure, asymmetric SCH LD has low threshold current density, low internal loss, and high and flat slope efficiency with respect to temperature.

Scanning differential spreading resistance microscopy on actively driven buried heterostructure multiquantum-well lasers

We have developed a new scanning probe microscopy-based technique, scanning differential spreading resistance microscopy (SDSRM), which enables the determination of free carrier distribution inside operating electronic and optoelectronic devices. The results of our SDSRM study of multiquantum-well (MQW) buried heterostructure (BH) lasers under zero and forward biases are reported. Individual QW-barrier layers can be resolved in high-resolution SDSRM. The SDSRM results show different internal carrier distribution within the MQW active region in BH lasers with and without biases and provide direct experimental evidence of electron overbarrier leakage. Our results demonstrate the utility of SDSRM to delineate quantitatively the transverse cross-sectional structure of complex two-dimensional devices such as MQW BH lasers under operating conditions, in which traditional probing such as secondary ion mass spectroscopy, scanning spreading resistance microscopy, and electron beam-induced current microscopy can either apply only to devices under zero bias or provide only qualitative pictures.

Comparison of GaInNAs Laser Diodes Based on Two to Five Quantum Wells

We have investigated GaInNAs-GaAsN multiquantum-well (MQW) lasers with two-QW (DQW), three-QW (TQW), and five-QW (5QW) active regions and emission in the 1.3-/spl mu/m range. A solid-source molecular beam epitaxy system has been used to grow the structures. Operation of a GaInNAs 5QW laser is reported. Low threshold currents of 22 (DQW) to 52 mA (5QWs) and external efficiencies of 0.25 W/A (DQWs) to 0.16 W/A (5QWs) per facet are realized under CW operation. T/sub 0/-values of 121 K are obtained.