Ridge formation for AlGaAs GRINSCH lasers by Cl2reactive ion etching

Optical storage applications for AlGaAs power lasers require single-mode laser operation and well-controlled beam divergence. For AlGaAs GRIN separate confinement heterostructure (GRINSCH) ridge lasers, these optical characteristics are sensitive to the precise ridge geometry of the laser. Directional reactive ion etching with Cl₂ and in situ monitoring of the etch with highly attenuated laser interferometry provide the excellent process control required during formation of the ridge. The process is described, and results are presented for lasers that were fabricated using this technique     

Multiquantum-well lasers with tapered active stripe for direct coupling to single-mode fiber

We demonstrate narrow beam divergence in 1.3-/spl mu/m wavelength multiquantum-well (MQW) lasers with an active stripe horizontally tapered over the whole cavity, for direct coupling to single mode-fibers. The lasers have reduced output beam divergence in a simple structure which does not contain an additional spot-size transformer. The fabricated laser shows narrow beam divergence of /spl sim/12/spl deg/, while a low-threshold current of 6.9 mA and a high efficiency of 0.62 mW/mA are realized. Furthermore, a direct-coupling efficiency to a single-mode fiber is -4.0-dB and -3-dB alignment tolerance is /spl plusmn/2.5 /spl mu/m.     

Preliminary reliability studies of 1.55 mu m graded index separate confinement buried heterostructure (GRINSCH) multiple quantum well (MQW) lasers grown by metalorganic vapour phase epitaxy (MOVPE)

1.55 mu m graded index separate confinement heterostructure (GRINSCH) multi-quantum-well (MQW) lasers, grown entirely by metalorganic vapour phase epitaxy (MOVPE), have demonstrated low degradation rates in lifetests at 50 degrees C, 4 mW per facet. These lasers are complex structures, containing many interfaces, and the encouraging early lifetest results demonstrate the ability of MOVPE to grow these structures.<>     

InGaAs/InGaAlAs MQW lasers with InGaAsP guiding layers grown by gas source molecular beam epitaxy

An InGaAs/InGaAlAs multiple-quantum-well (MQW) laser was grown by gas source molecular beam epitaxy (GS-MBE). The laser has InP cladding layers and InGaAsP guiding layers, and the active layer is composed of an InGaAs/InGaAlAs MQW layer. Electrons are injected into the MQW active layer by tunneling through the barriers. The threshold current of the InGaAs/InAlAs buried-heterostructure (BH)-MQW lasers was as low as 9.6 mA. The relaxation oscillation frequency of the InGaAs/InAlAs MQW lasers was found to be larger than that of the InGaAs/InGaAsP MQW lasers with the same structure.<>     

Vertical integration of an In/sub 0.15/Ga/sub 0.85/As modulation-doped field effect transistor and GaAs laser grown by molecular beam epitaxy

A vertically integrated structure consisting of an In/sub 0.15/Ga/sub 0.85/As pseudomorphic modulation doped field effect transistor (MODFET) and a GaAs graded index separate confinement heterostructure single quantum well (GRINSCH SQW) laser was grown by molecular beam epitaxy. Wafers containing integrated MODFET/laser layers produced MODFETs with DC and microwave performance comparable to wafers containing only MODFET layers, indicating that the modulation doping and the strained In/sub 0.15/Ga/sub 0.85/As channel were largely unaffected by the long, high temperature laser growth. The lasers had threshold currents similar to identical structures grown on n-type substrates and the integrated structures had a -3dB modulation bandwidth of 3.5 GHz.<>     

Electrically pumped circular-grating surface-emitting DBR laser onInGaAs strained single-quantum-well structure

The authors demonstrate the fabrication and room temperature operation of an electrically pumped circular-grating surface-emitting distributed-Bragg-reflector laser. An InGaAs/GaAs single quantum well (SQW) graded-index separate confinement heterostructure (GRINSCH) structure was grown by one-step molecular beam epitaxy (MBE). Circular gratings were defined by focused ion beam lithography. The lasing wavelength was 942 nm, and the threshold current was 280 mA. This is the first demonstration of these lasers with no epitaxial regrowth     

Finite-element modeling of one- and two-dimensional MQWsemiconductor optical waveguides

A finite-element characterization of optical waveguides incorporating multiple-quantum-well (MQW) structures is presented. Optical modeling of a planar MQW region is tested to verify that the quantum-well region can be replaced by a homogeneous region with a suitable effective index. Optical modeling of a semiconductor laser incorporating MQW regions with two-transverse-dimensional confinement is then used to identify the range of single-lateral-mode operation. The effective index, the power fraction in the active region, and the spot size dependence on the total optical power for the case of a self-defocusing MQW region are also presented     

Low threshold current GaAs/AlGaAs GRIN-SCH lasers grown bymolecular beam epitaxy on Si3N4 masked substrates

High-performance single-quantum-well graded-refractive index separate confinement heterostructure (SQW GRINSCH) laser have been grown by molecular beam epitaxy on Si₃N₄ patterned GaAs (100) substrates. Lasers grown on stripe windows orientated in the [011] direction have optical waveguiding and current confinement supplied by facetting occurring during growth. Lasers fabricated on 10 μm wide Si ₃N₄ openings have threshold currents as low as 15 mA for a 500 μm-long cavity. The current density required to reach optical transparency is 144 A/cm²; an internal quantum efficiency of 81%, and a peak optical power of 70 mW per facet has been obtained. Device performance comparable to ridge lasers is observed in a self-aligned laser process     

1.55-μm InGaAsP-InP spot-size-converted (SSC) laser with simpletechnological process

In this letter, we report the realization of a 1.55-μm spot-size-converted (SSC) laser using conventional SCH-MQW active layers and conventional photolithography. The laser consists of a 300-μm-long rectangular gain section, with compensated multiple-quantum-well (MQW) structure, and a 300-μm-long tapered passive waveguide, fabricated on lower SCH layer. The device exhibits a beam divergence of 13°×18° and 3.5-dB coupling loss with a cleaved single-mode fiber (SMF). The 1-dB alignment tolerance is ±2.3 μm in the vertical direction and ±1.9 μm in the lateral direction, respectively     

Design of quantum well AlGaAs-GaAs stripe lasers for minimizationof threshold current-application to ridge structures

The gain saturation effect and the various leakage currents related to a strip structure (spreading current, lateral diffusion current, optical cavity recombination current, and Auger recombination current) are considered. The minimum threshold current (3.3 mA) is obtained with a multiquantum-well (MQW) structure (5×80 Å) at a cavity length of 80 μm. At these values, the lateral leakage current (spreading and lateral diffusion currents) represents about 50% of the threshold current. It is shown that for short-cavity lasers, the MQW is preferred to the SQW (single-quantum-well) structure. However, the well number in the active layer of a ridge structure is limited by the decrease of the parallel confinement and the increase of the lateral leakage current. Finally, good agreement was obtained in comparing the calculations with experimental results for GRINSCH (graded-index separate-confinement heterojunction) SQW lasers     

Room-temperature operation of MBE-grown InGaP/InGaAlP MQW visible laser diodes

Room-temperature pulsed operation has been achieved, for the first time, in InGaP/InGaAlP multiquantum-well (MQW) laser diodes grown by molecular beam epitaxy (MBE). This MQW laser is composed of 10 nm-thick InGaP well layers and 5 nm-thick InGaAlP barrier layers. The lasing wavelength was 658 nm. The threshold current density and T0 value were 7.6 kA/cm2 and 115 K, respectively.     

Fabrication of short GaAs wet-etched mirror lasers and theircomplex spectral behavior

A versatile fabrication technique for GaAs-AlGaAs wet-etched mirror lasers is presented. This technique works independently of the Al concentration in the cladding layers up to a value of 70%, and it requires four photolithography steps. Ridge waveguide lasers have been successfully processed using a double heterostructure (DHS) as well as graded index separate confinement heterostructures (GRINSCH) having different quantum-well (QW) active layers. This technique is used to fabricate short-cavity lasers in GRINSCH structures having GaAs multiple-quantum-well (MQW) or bulk active layers. Laser operation was obtained in a 29-μm-long device using a 5-QW structure. Short lasers with QW active layers show a complex spectral behavior. These lasers operate at higher current densities (~20 kA/cm²) and emit light at more than one wavelength. This implies that higher order transitions are involved which is not the case when using a bulk GaAs active layer. Besides the two peaks corresponding to the n=1 and n=2 transitions, we found an intermediate peak which corresponds presumably to the forbidden transition E1-HH2     

GaxIn1-xAsyP1-y-InPtensile-strained quantum wells for 1.3-μm low-threshold lasers

Ga_xIn_1-xAs_yP_1-y-InP tensile-strained multiple quantum wells (MQWs) grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) are studied for the application to 1.3-μm lasers. High-resolution X-ray diffraction curves show good agreement with theoretical simulation. Clear energy separation of light hole and heavy hole bands is observed in the room temperature photoluminescence measurement. Threshold characteristics of -1.15% tensile-strained MQW lasers with graded index separate confinement heterostructure (GRINSCH) are investigated. The minimum threshold current density per well (J_th/N_w) for infinite cavity length obtained is 100 A/cm² for the device with a well number of 3. Tensile strain dependence of J_th/N _w for an infinite cavity is also clarified     

Monolithic integration of a quantum-well laser and an opticalamplifier using an asymmetric twin-waveguide structure

We demonstrate the monolithic integration of a 1.55 μm wavelength InGaAsP-InP multiple-quantum-well (MQW) laser and a traveling-wave optical amplifier using an asymmetric, vertical twin-waveguide structure. The laser and amplifier share the same strained InGaAsP MQW active layer grown by gas-source molecular beam epitaxy, while the underlying passive waveguide layer is used for on-chip optical interconnections between the active devices. The asymmetric twin-waveguide structure uses the difference in modal gains to discriminate between the even and odd modes     

Room temperature CW operation ofGa0.3In0.7As/GaInAsP/InP strained MQW lasers withwire active region

A room temperature CW operation of Ga_0.3In_0.7As/GaInAsP/InP GRINSCH compressive strained MQW lasers with 30~60 nm wide wire active region was achieved. This device was fabricated by two-step LP-OMVPE growths on p-type InP substrate and wet chemical etching. Threshold current as low as 53 mA ( L=910 μm, J_th=2.9 kA/cm²) was obtained at RT-CW condition. The spontaneous emission peak and the lasing wavelength of strained MQW wire lasers exhibited approximately 20-meV blue shift from those of MQW film lasers cut out from the same wafer     

1.3-μm InAsP modulation-doped MQW lasers

The effect of both n-type and p-type modulation doping on multiple-quantum-well (MQW) laser performances was studied using gas-source molecular beam epitaxy (MBE) with the object of the further improvement of long-wavelength strained MQW lasers. The obtained threshold current density was as low as 250 A/cm² for 1200-μm-long devices in n-type modulation-doped MQW (MD-MQW) lasers. A very low CW threshold current of 0.9 mA was obtained in 1.3-μm InAsP n-type MD-MQW lasers at room temperature, which is the lowest ever reported for long-wavelength lasers using n-type modulation doping, and the lowest value for lasers grown by all kinds of MBE in the long-wavelength region. Both a reduction of the threshold current and the carrier lifetime in n-type MD MQW lasers caused the reduction of the turn-on delay time by about 30%. The 1.3-μm InAsP strained MQW lasers using n-type modulation doping with very low power consumption and small turn-on delay time are very attractive for laser array applications in high-density parallel optical interconnection systems. On the other hand, the differential gain was confirmed to increase by a factor of 1.34 for p-type MD MQW lasers (N_A=5×10¹⁸ cm ^-3) as compared with undoped MQW lasers, and the turn-on delay time was reduced by about 20% as compared with undoped MQW lasers. These results indicate that p-type modulation doping is suitable for high-speed lasers     

A novel SAL-PINSCH quantum-well laser structure for a pinched beamdivergence

Summary form only given. An edge-emitting strained AlGaAs/InGaAs/GaAs quantum-well laser structure is reported. It has a periodic index separate confinement heterostructure (PINSCH) optical confinement layers for a small beam divergence and high output power. Preliminary measurements of AR/HR-coated self-aligned ridge waveguide lasers show a CW output power of up to 350 mW and a 20° transverse beam divergence at a 980-nm lasing wavelength. This low beam divergence results in a high coupling efficiency of 51% into single-mode fibers. The expanded optical field in PINSCH confinement layers significantly pinches the transverse beam divergence and increases the maximum output power     

ATP跟瞄精度与最佳信号光发射角的研究

激光星间通信中捕获、跟踪、瞄准(ATP)技术是保障通信正常进行的关键一环，在完成捕获进入跟踪状态下，ATP的跟瞄精度是一个重要指标。然而．在实际系统中，ATP的跟瞄精度受到很多因素的制约．只能达到一定的精度。在这种条件下．信号光束发散角的选取对通信系统的整体性能影响很大。提出了影响光束发散角的三种因素，并进一步分析了在给定跟瞄精度的条件下．信号光束的发散角并不是越小越好而是存在一个最佳发散角．该发散角可以在满足通信系统指标的情况下．对发射端的功率需求最小。     

Analysis and application of theoretical gain curves to the design of multi-quantum-well lasers

Gain/current curves for a single quantum well are calculated. The optimum well number, cavity length, threshold current, and current density of multi-quantum-well (MQW) lasers are derived in terms of this gain curve. The limiting performance of MQW lasers is found to be better than that of graded refractive index (GRIN) lasers, assuming comparable efficiencies and spontaneous emission linewidths. The optimum threshold current for an MQW laser with a 7 μm cavity and 90 percent facet reflectivity issim50 muA/μm.     

Long wavelength waveguide multiple quantum well optical modulators

The first measurements of large anisotropic modulation of long-wavelength light with a large on/off ratio and low driving voltage propagating along the plane of InGaAs/InAlAs multiple quantum well (MQW) structures grown by molecular beam epitaxy (MBE) are reported. Photocurrent response and optical modulation of waveguide pin diodes is measured for incident light polarization parallel and perpendicular to the MQW layers emitting from a color center laser. The incident-light power and wavelength dependence of on/off ratio are also determined.