GaInAs/InP quantum wires grown by metalorganic vapor phase epitaxy on V-grooved InP substrates

A single nominally lattice matched GaInAs quantum well (QW)/quantum wire (QWR) structure was grown by metalorganic vapor phase epitaxy (MOVPE) in V-grooved InP substrates. Different Si0₂ etch masks with opening widths from 2 μm down to 200 nm (for application as second order DFB grating) were defined by optical and electron beam lithography. A damage-reduced wet chemical etching process enables the growth of the GaInAs QWs/QWRs without any InP buffer layer. In low temperature photoluminescence we found improved intensity for all wire structures prepared by this etching technique. A reduction of the period and opening width of the V-groove etch mask resulted in a optimized luminescence intensity ratio between QW and QWR. Decay times from time resolved luminescence measurements were compared to the decay times of wet or dry etched mesa wires before and after regrowth. The good optical properties of the GaInAs QWRs are encouraging for future application as a QWR-laser device.     

Fabrication of AlGaAs-GaAs quantum-wire gain-coupled DFB lasers bya single MOCVD growth step

AlGaAs-GaAs quantum-wire (QWR) gain-coupled distributed-feedback (GC-DFB) lasers have been fabricated by a single metal-organic chemical vapor deposition growth step on 0.36-μm pitch V-groove arrays of GaAs. A record low-threshold current of 13 mA is achieved via DFB lasing from QWR gain at room temperature. The consistency of the photon energies of the lasing and the photoluminescence peaks from QWR, and about 4-nm-wide stopband with a large threshold gain difference observed in the near-threshold spectrum are presented as possible evidence for GC-DFB effects in these devices     

Realization of Vertically Stacked InGaAs/GaAs Quantum Wires on V-grooves with (322) Facet Sidewalls by Chemical Beam Epitaxy

We report, for the first time, the fabrication of vertically stacked InGaAs/GaAs quantum wires (QWRs) on V-grooved substrates by chemical beam epitaxy (CBE). To fabricate the vertically stacked QWRs structure, we have grown the GaAs resharpening barrier layers on V-grooves with (100)-(322) facet configuration instead of (100)-(111) base at 450 °C. Under the conditions of low growth temperature, the growth rate of GaAs on the (322) sidewall is higher than that at the (100) bottom. Transmission electron microscopy verifies that the vertically stacked InGaAs QWRs were formed in sizes of about 200Å × 500 ~ 600 Å. Three distinct photoluminescence peaks related with side-quantum wells (QWLs), top-QWLs and QWRs were observed even at 200 K due to sufficient carrier and optical confinement. These results strongly suggest the existence of the quantized state in the vertically stacked InGaAs/GaAs QWRs grown by CBE.     

AlGaAs/GaAs quantum wire lasers fabricated by flow rate modulationepitaxy

AlGaAs/GaAs quantum wire lasers, with three quantum wires (QWRs) of almost identical physical size, have been fabricated by flow rate modulation epitaxy. Room temperature lasing from the ground state electron and heavy-hole (le-lhh) transition of the QWRs has been observed for the first time. Typical threshold currents of 6 mA and extremely minor wavelength shifts in emission spectra have been obtained     

Analysis of Compressively Strained GaInAsP–InP Quantum-Wire Electro-Absorption Modulators

Performance of compressively strained (CS) GaInAsP-InP quantum-wire (QWR) electro-absorption modulators (EAMs) is theoretically studied using an eight-band kldrp model. An empirical relationship is proposed for the quantum-confined Stark shift in QWR EAMs. The accuracy of this relationship is verified by comparing with numerical data. The effects of the variation of different device parameters on the absorption spectra are investigated. The absorption peaks are found to be stronger in narrower QWRs with strain-compensating barriers. Comparison of the extinction ratio with that of similar quantum-well EAMs show that, in spite of the lower in-plane filling factor, QWR EAMs exhibit a higher extinction ratio. Effect of fluctuation of wire width on the absorption spectrum of QWRs has been studied. The proposed QWR EAMs are suitable for photonic integrated circuits (PICs) fabricated by electron-beam lithography, reactive-ion etching, and two-step epitaxial growth. Due to the nature of the integration in such structures, the QWR EAMs are not required to be polarization-insensitive. On the contrary, the QWR EAMs are naturally tuned to the polarization of the output of the CS QWR lasers, fabricated on the same PIC, leading to an enhancement of the absorption strength. Moreover, the QWR EAMs, integrated with QWR lasers, offer low insertion loss.     

Cavity-length-dependent spectral and temporal characteristics ofthe gain switched V-groove quantum-wire laser

The cavity-length-dependent spectral and temporal characteristics of a V-groove AlGaAs-GaAs quantum-wire (QWR) laser are investigated. At short cavity lasers less than 300-μm, a discrete wavelength switching from the first (n=1; 837.7 nm for the 800-μm cavity) to the second (n=2;826.5 nm for the 220-μm cavity) subbands occurs due to the increased threshold gain, resulting from the increased cavity loss. Utilizing this characteristic, ultrafast lasing behaviors at the n=1 and n=2 quantized transitions of the QWR, generated by the gain-switching method, are demonstrated and compared     

Longitudinal mode behaviors of 1.5 µm range GaInAsP/InP distributed feedback lasers

Longitudinal mode behaviors of asymmetric structure distributed feedback buried heterostructure (DFB-BH) lasers are examined theoretically and experimentally. A 1.5 μm range GaInAsP/InP DFB-BH laser was fabricated by a three-step LPE growth process. We measured the stopband in the spectrum of the DFB laser. It was found that no resonance mode emission occurred in the gain spectrum and its spectrum was asymmetric with respect to the Bragg wavelength. Most of the lasing power concentrated on the DFB mode adjacent to the stop-band which was determined by the Bragg condition. The measured spectrum was explained by the calculated results of the coupled wave theory with external reflectors. The asymmetric spectrum was caused by the relative position of the cleaved facet on the corrugation grating. It was shown that the asymmetric structure DFB laser, which consisted of two end facets with different reflection coefficients, gives a stable single longitudinal mode. There was no mode jump up to 2.3 times threshold. At a modulation depth of 100 percent, the ratio of the highest nonlasing mode intensity to the lasing DFB mode was estimated to be -16.0 dB.     

Detuning adjustable multiwavelength MQW-DFB laser array grown byeffective index/quantum energy control selective area MOVPE

A multiwavelength MQW DFB laser array with novel structure Is described. Oscillation wavelength and gain peak wavelength were simultaneously controlled on the same epitaxial wafer by using modulated grown thicknesses of selectively grown InGaAs/InGaAsP/InP MQW active waveguides. The laser array with constant-pitch built-in corrugation fabricated by a simple DFB laser process demonstrated 10.1 nm controllable range for lasing wavelength and 45 nm for gain peak wavelengths, with uniform lasing properties and narrow spectral linewidths. The technique is attractive for light sources used in WDM/FDM applications     

Ultra-High speed InGaAsP/InP DFB lasers emitting at 1.3 µm wavelength

A bandwidth of 13 GHz has been attained in a 1.3 μm DFB laser at 25 °C. A mesa structure was introduced to reduce the parasitic capacitance and the lasing wavelength was detuned from the gain peak to increase the differential gain. This bandwidth is the widest so far reported in 1.3 μm DFB lasers.     

Wide temperature range of stable single-mode operation in weakly coupled asymmetric mirror reflectivity DFB lasers

A maximum difference between the peak gain wavelength and the lasing wavelength where stable DFB mode operation is achieved has been obtained for weakly coupled (KL?; 0?7), asymmetric mirror structure (Rf = 5%, Rr = 31%) DFB lasers. DFB lasers optimally fabricated exhibit single-longitudinal-mode operation over a wide temperature range of 5?100°C.     

InAs-InAlGaAs quantum dot DFB lasers based on InP [001]

The InAs-InAlGaAs quantum dot (QD) lasers with the InAlGaAs-InAlAs material system were fabricated on distributed feedback (DFB) grating structures on InP [001]. The single-mode operation of InAs-InAlGaAs QD DFB lasers in continuous-wave mode was successfully achieved at the emission wavelength of 1.564 /spl mu/m at room temperature. This is the first observation on the InP-based QD lasers operating around the emission wavelength window of 1.55 /spl mu/m. The threshold current density of the InAs-InAlGaAs QD DFB laser with a cavity length of 1 mm and a ridge width of 3 /spl mu/m, in which one of the cleaved facets was coated with 95% high-reflection, was 1.23 kA/cm/sup 2/ (176 A/cm/sup 2/ for single QD layer). The sidemode suppression ratio value of the QD DFB laser was as high as 42 dB at the driving current of 100 mA.     

半导体量子阱激光器（QWL）及其进展

由于半导体量子阱结构限制电子和空穴到极薄区域的量子尺寸效应,导致了它具有二维台阶状的态密度。因此,用这种结构制备的量子阱激光器(QWL)具有低的阈值电流密度,窄的谱线宽度,宽的波长调谐范围以及高的调制频率响应知易实现大功率、短波长可见光输出等优点。本文在描述了这种结构的台阶状态密度分布的基础上,主要介绍了 QWL 主要优异特性和最近的发展水平。最后对今后的发展方向作了预测。     

Super-flat (411)A interfaces and uniformly corrugated (775)B interfaces in GaAs/AlGaAs and InGaAs/InAlAs heterostructures grown by molecular beam epitaxy

Extremely flat interfaces, i.e. effectively atomically flat interfaces over a wafer-size area were realized in GaAs/AlGaAs quantum wells (QWs) grown on (411)A GaAs substrates by molecular beam epitaxy (MBE). These flat interfaces are called as “(411)A super-flat interfaces”. Besides in GaAs/AlGaAs QWs, the (411)A super-flat interfaces were formed in pseudomorphic InGaAs/AlGaAs QWs on GaAs substrates and in pseudomorphic and lattice-matched InGaAs/InAlAs QWs on InP substrates. GaAs/AlGaAs resonant tunneling diodes and InGaAs/InAlAs HEMT structures with the (411)A super-flat interfaces were confirmed to exhibit improved characteristics, indicating high potential of applications of the (411)A super-flat interfaces. High density, high uniformity and good optical quality were achieved in (775)B GaAs/(GaAs)_m(AlAs)_n quantum wires (QWRs) self-organized in a GaAs/(GaAs)_m(AlAs)_n QW grown on (775)B GaAs substrates by MBE. The QWRs were successfully applied to QWR lasers, which oscillated at room temperature for the first time as QWR lasers with a self-organized QWR structure in its active region. These results suggest that MBE growth on high index crystal plane such as (411)A or (775)B is very promising for developing novel semiconductor materials for future electron devices.     

Long-wavelength InGaAsP/InP distributed feedback lasersincorporating gain-coupled mechanism

Successful operation of long-wavelength InGaAsP low-threshold-current gain-coupled DFB lasers was demonstrated by using an InGaAsP quaternary grating that absorbs the DFB (distributed feedback) emission. The amount of gain (loss)-coupling is controlled by the composition (bandgap) and thickness of the grating quaternary and the InP-spacer layer between the grating and the active layer. With optimally designed lasers, CW (continuous-wave) threshold currents were 10-15 mA (250-μm cavity, as-cleaved), slope efficiency was ~0.4 mW/mA (both facets) and SMSR (side-mode suppression ratio) was as high as 52 dB. The laser operated in the same DFB mode with SMSR staying ~50 dB throughout the entire current range. At 100°C, the CW threshold current stayed low, ~50 mA, and SMSR was ~40 dB. Results also indicate that the presence of gain-coupling removes the degeneracy in lasing wavelength     

Quantum wire lasers

Recent progress in the development of the concept and technology of semiconductor quantum wire (QWR) lasers is reviewed. In these quasi-one-dimensional structures, optical gain is provided by charge carriers that are quantum mechanically confined in two dimensions within wire-like active regions. These devices are expected to exhibit improved laser performance, including extremely low threshold currents (in the μA range), higher modulation bandwidth, narrower spectral linewidth, and reduced temperature sensitivity. QWR lasers would thus be particularly useful in applications involving densely packed laser arrays and monolithic integration of lasers with low-power electronics, including computer optical interconnects, optical computing, and integrated optoelectronic circuits. Approaches for fabricating these novel structures are reviewed, and recent successful demonstrations of lasing in semiconductor QWRs are described. Prospects for further progress in this area are also discussed     

Wavelength shift enhancement in quantum-well intermixeddistributed-feedback lasers

The maximum possible shift in emission wavelength of a quantum-well (QW) intermixed distributed-feedback (DFB) laser as a function of degree of intermixing is studied. In a recent experiment, the wavelength shift of a QW intermixed DFB laser is around 13% of the bandgap blue shift. Our study indicates that if a smaller grating period is used, the wavelength shift can be increased by four times to 50% of the bandgap blue shift, because it is not necessary to change the carrier density significantly in order to maintain a modal gain above lasing threshold. The maximum tuning range is found to be 20 nm, indicating that QW intermixing can be used to fabricate multiwavelength DFB laser arrays for wavelength-division-multiplexing communication systems     

Second-order DFB lasers fabricated by deep UV contact lithography and GSMBE

DFB ridge waveguide lasers at 1.55 mu m with uniform second-order gratings defined by deep UV lithography have been realised for the first time. The lasers have been fabricated using gas source molecular beam epitaxial (GSMBE) heterostructures grown in a two-step process. The characteristics of the DFB lasers (28 mA minimum threshold current, single-mode behaviour at output power in excess of 5 mW for more than 80% of the lasers and very low dispersion (+or-0.6 nm) of the lasing wavelength) demonstrate that deep UV lithography can be successfully used for the fabrication of DFB lasers.<>     

1.52-1.59-μm range different-wavelength modulator-integratedDFB-LDs fabricated on a single wafer

We report for the first time different-wavelength modulator-integrated distributed-feedback laser diodes (DFB/MODs) fabricated on a single wafer, whose lasing wavelength cover almost all of the expanded erbium-doped fiber amplifier (EDFA) gain band from 1.527 to 1.593 μm. The devices provided uniform and high-performance characteristics such as a threshold current less than 12 mA and successful transmission of 2.5 Gb/s-600 km through a normal fiber     

Electrical control of the distributed feedback organic semiconductor laser based on holographic polymer dispersed liquid crystal grating

In this paper, we demonstrate the electrical control of the distributed feedback (DFB) organic semiconductor laser based on a holographic polymer dispersed liquid crystal (HPDLC) grating for the first time. The grating is fabricated on the top of the organic semiconductor film to act as an external feedback structure. Experimental results show that the lasing intensity can be decreased by increasing the external electric field, and the lasing wavelength exhibits a slight blue-shift of 1.4 nm during the modulation process, indicating a good stability. The modulated performances are attributed to the decreases in the refractive index modulation and average refractive index of the HPDLC grating respectively as a result of the field-induced liquid crystal reorientation. This study provides some new ideas for the improvement of DFB organic semiconductor laser to enable envisioned applications in laser displays and integrated photonic circuits.     

A unified Green's function analysis of complicated DFB lasers

An efficient full-wave analysis technique for one-dimensional optical domains, known as the recursive Green's function method (RGFM), is presented for evaluation of distributed feedback (DFB) laser cavities with arbitrary material profiles. The method first constructs the Green's function of an inhomogeneous domain and subsequently uses Green's theorem to determine the laser optical field, lasing wavelength, and threshold gain. The technique is applied to investigate the performance of three DFB laser structures: a chirped-grating configuration, a modulated stripe width design, and a reduced duty cycle complex-coupled device. These structures are evaluated in terms of their single-mode lasing behavior and the uniformity of the optical field within the cavity