InGaAsP InP current confinement mesa substrate buried heterostructure laser diode fabricated by one-step liquid-phase epitaxy

New InGaAsP/InP buried heterostructure laser diodes fabricated by one-step liquid-phase epitaxy are described, in which the InGaAsP active region completely embedded in InP is grown on the top of the mesa stripe formed on the InP substrate while, simultaneously, current confinement structure is automatically formed on both sides of the mesa stripe. These current confinement mesa substrate buried heterostructure laser diodes (CCM-LD's) have current confinement structure which very effectively blocks unwanted leakage current bypassing the light emitting region which has enabled laser operation with a threshold current as low as 20 mA, 70-mW maximum CW output at room temperature, and 125°C maximum CW operation temperature. Life tests over 6000-h CW operation at 70°C and 5 mW/facet have confirmed good reliability of these devices.     

Characteristics of diffused-stripe InP/InGaAsP/InP lasers emitting around 1.55 µm

Fabrication and lasing characteristics of InGaAsP/InP lasers emitting around 1.55 μm are described. Zn-diffused stripe-geometry lasers with emission wavelengths in the1.53-1.60mum range were fabricated from InP/InGaAsP/InP DH epitaxial wafers prepared by a low temperature LPE technique. The dependence of the lasing charaeteristics on the stripe width was examined. The lowest threshold current (≃160 mA under CW operation at 27°C) was obtained for a laser with a 13 μm stripe. CW operation of the laser has been achieved at a heat-sink temperature as high as 53°C. For sufficiently narrow stripe widths (simeq6 mum), fundamental-transverse mode and single-longitudinal mode operation was obtained under CW operation. Moreover, the lasers have good high-frequency performance. The lasers showed excellent dynamic properties without waveform distortion under high-frequency (800 Mbits/s) large-signal pulse modulation. The full width at half maximum of the longitudinal mode envelope was approximately 30 Å at 800 Mbits/s.     

Optimum design conditions for AlGaAs window stripe lasers

The maximum available CW optical power from the AlGaAs window stripe laser was investigated both theoretically and experimentally. It is found that a thin third AlGaAs layer thickness and high-quality pulsed lasing characteristics, such as low threshold current density and high external differential quantum efficiency, which are obtained from refractive index guiding and short window-region length, are necessary to increase CW optical power. Stable fundamental lateral transverse mode CW operation was achieved at 55 mW (∼4.7 MW/cm²) in a window stripe (WS) laser with 3 μm stripewidth, which is about five times higher than the typical catastrophic optical damage (COD) threshold in conventional structure lasers. It was also found that a high-quality window stripe laser with 3 μm stripewidth operated at 30 mW (∼2.6 MW/cm²) for more than 3500 h.     

InGaAsP double-channel- planar-buried-heterostructure laser diode (DC-PBH LD) with effective current confinement

A new high-performance 1.3-μm InGaAsP semiconductor laser is described, in which effective current confinement into the active region has been realized. A p-n-p-n current blocking structure is made by liquid-phase epitaxy (LPE) on both sides of the active-stripe mesa which is defined by a pair of channels in the double-heterostructure wafer. The double-channel-planar-buried-heterostructure laser diodes (DC-PBH LD's) exhibit high-laser performances, such as a high differential quantum efficiency of 78-percent maximum, which results in high electrical to optical power conversion efficiency 43 percent, and high light output power of over 50 mW, as a result of the improvement in the current blocking structure. The threshold current temperature sensitivity is found experimentally to be reduced remarkably by increasing the doping concentration in the p-cladding layer. Characteristic temperature as high as 100 K has been obtained. CW operation is possible up to 130°C.     

1.5 µm range InGaAsP/InP distributed feedback lasers

Lasing characteristics of InGaAsP/InP distributed feedback (DFB) lasers in the 1.5 μm range were studied theoretically and experimentally. Wave propagation in five-layer DFB waveguides were analyzed to estimate the effect of the structural parameters on threshold conditions. A brief consideration on designing a low threshold laser and its lasing wavelength was made. DFB buried heterostructure lasers with fundamental grating emitting at 1.53 μm were prepared by liquid phase epitaxial techniques. CW operation was confirmed in the temperature rangeof -20° to 58°C, and a CW threshold current was as low as 50 mA at room temperature. A stable single longitudinal mode operation was observed both in dc condition and in modulated condition by a pseudorandom pulse current at 500 Mbits/s. No significant increase in the threshold current was observed after 1400 h continuous CW operation at 20°C.     

MOCVD-grown broad area InGaAs/GaAs/InGaP laser diodes

A MOCVD technology for growth of InGaAs/GaAs/InGaP laser heterostructures on a modified Epiquip VP-50-RP installation was developed. Mesa stripe laser diodes with threshold current density J _th=100–200 A/cm², internal optical loss α_i=1.3–1.7 cm^?1, and internal quantum efficiency η_i=60–70% have been fabricated. A CW output optical power of 5 W has been obtained for a single 100-µm-wide aperture mesa stripe laser diode emitting at 1.03 µm. It is shown that use of AlGaAs waveguide layers, which increase the conduction band barrier offset, lowers the temperature sensitivity of laser heterostructures within the temperature range 10–80°C.     

Low threshold InGaAsP/InP buried crescent laser with double current confinement structure

An InGaAsP/InP laser diode emitting at 1.3 μm with a crescent shaped active region is described. The active region is completely embedded in InP by a two-step LPE technique, and a double current confinement scheme is incorporated with two reverse biased p-n junctions at both sides of the active layer. A threshold current as low as 20 mA has been achieved in CW operation at room temperature. Fundamental transverse mode operation with linear light output-current characteristics and single longitudinal mode oscillation have been obtained.     

InGaAsP/InP separated multiclad layer stripe geometry lasers emitting at 1.5 ?m

InGaAsP/InP separated multiclad layer stripe geometry lasers emitting at 1.5 ?m are reported. The CW threshold current at 25°C is only 82 mA and the maximum temperature where CW lasing is obtained is 65°C. The characteristic temperature of the pulsed threshold current is 60 K. The transverse mode is fundamental and the longitudinal mode is single up to 1.5 times the threshold under CW operation. A few samples operated for over 1000 h at 50°C under constant optical power operation of 5 mW/facet.     

Separated multi clad-layer stripe-geometry GaAlAs DH laser

The fabrication process, the analysis of the waveguiding property, and the lasing characteristics of a separated multiclad-layer (SML) stripe-geometry laser for a 0.8 μm wavelength are described. The SML stripe geometry enables us to grow at 820°C a flat active layer without deformation of the shape of the grow by melt-etching. The analysis shows that the built-in waveguide is the effective refractive index step waveguide, in contrast to the loss step waveguide of the CSP laser, and we can fabricate a laser with small stripewidth. The fundamental transverse and longitudinal single-mode lasing were obtained with CW threshold current of 45-70 mA for the stripewidth3-6 mum. The damped relaxation oscillation and the small spectral broadening when modulated by 400 Mbits/s RZ random pulses were obtained. A small increase rate of the driving current when operated at 50°C with 5 mW/facet output was confirmed.     

Low-threshold distributed feedback lasers fabricated on material grown completely by LP-MOCVD

GaInAsP-InP distributed feedback (DFB) lasers emitting at 1.57 μm have been fabricated on material grown completely by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The CW threshold current of 60 mA and an output power of 6 mW per facet at room temperature have been obtained. The lasing wavelength λLunder CW operation showed a temperature coefficient (d_{lambdaL}/dT) of 0.9 Å/°C for this DFB laser over the range of10-90degC. A stable single longitudinal mode was maintained under high speed pulse modulation up to 500 ps, and sinusoidal modulation at 1 Ghz.     

MBE growth and characteristics of periodic index separate confinement heterostructure InGaAs quantum-well lasers

We have used solid-source molecular beam epitaxy (MBE) to grow InGaAs quantum-well lasers emitting at 980nm in a novel configuration of periodic index separate confinement heterostructure (PINSCH). Periodic multilayers (GaAs/AlGaAs) are utilized as optical confinement layers to reduce the transverse beam divergence as well as to increase the maximum output power. The multilayers are grown by temperature modulation MBE without any shutter operation. The heterointerfaces in the multilayers are linearly graded such that the energy barrier heights are greatly decreased. This has led to a drastic reduction in the series resistance which is essential in the performance of high output power. The 5μm × 750μm device has far-field angles of 10° by 20°, a threshold current of 45 mA, an external differential quantum efficiency of 1.15 mW/mA (90%), and an output power of 620 mW, all measured at room temperature under CW operation. A record high fiber coupling efficiency of 51% has been achieved and more than 130 mW of power is coupled into a 5μm-core single mode fiber.     

The temperature dependence of internal optical losses in semiconductor lasers (λ = 900–920 nm)

The temperature dependences of radiative characteristics of semiconductor lasers based on asymmetric heterostructures of the separate confinement with an extended waveguide fabricated by MOCVD epitaxy (the emission wavelength λ = 900–920 nm) are studied. It is established that the threshold concentration in the active region and waveguide layers of the laser heterostructure of the separate confinement increases in the CW lasing mode as the pumping current and temperature of the active region are increased. It is established experimentally that, in the temperature range of 20–140°C, the stimulated quantum yield remains unchanged. It is shown that the temperature delocalization of charge carriers leads to an increase in the carrier concentration in the waveguide layers of the laser heterostructure. The total increase in internal optical losses due to scattering by free charge carriers in the layers of the active region and waveguide layers of the laser heterostructure leads to a decrease in the differential quantum efficiency and to saturation of the watt-ampere characteristic of semiconductor lasers in the continuous lasing mode.     

Lateral confinement InGaAsP superluminescent diode at 1.3 µm

A superluminescent diode (SLD) has properties, based on the degree of coherence, that are bounded by those of the light emitting diode and the laser diode. The SLD can be designed to meet a wide range of optical system needs. By introducing ridge-waveguide lateral confinement, a good anti-reflection coating at one end and a high reflectivity mirror at the other, we have demonstrated an SLD that allows 30 percent coupling efficiency into a lensed 0.23 NA, 50 μm diameter graded index core fiber. The power in the fiber is 550 μW at 250 mA and 20°C. It is possible to maintain a constant power level in the fiber greater than 250 μW over the temperature range 0 to 35°C by adjusting the current. The spectral width is 300 Å and the modulation bandwidth 350 MHz. PCM with 400 Mbit/s rate has been observed. These devices are relatively easy to fabricate from ridge-waveguide lasers or any other lateral confinement laser.     

The heteroepitaxial ridge-overgrown distributed feedback laser

A new distributed feedback laser, the heteroepitaxial ridge-overgrown distributed feedback (HRO-DFB) laser, is proposed and demonstrated. The growth steps permit post-active-layer growth determination of the grating period, and the fabrication of this laser is simple with an automatic alignment of the current confinement to the ridge-overgrowths, which form the strip-loaded waveguide of the laser. The lateral overgrowth extending over the oxide films on both sides of the window stripe enhances the effect of grating feedback. Both LPE and MO-CVD have been employed successfully for the ridge overgrowth. The HRO-DFB laser was shown to operate in stable single-longitudinal mode with no observable mode partition events under 2 Gbit/s pseudorandom pulse modulation. The dynamic spectral width under 2 Gbit/s modulation was typically 0.5-2 Å. Other characteristics of these 1.5 μm HRO-DFB lasers include ∼8 mW/facet of single-longitudinal mode output power, and narrow beam divergence of 10° operating in the fundamental transverse mode in the junction plane. The CW thresholds were usually 50-100 mA. Transmission experiments with dispersive fibers (17 ps/km-nm) atsim1.55 mum at 2 Gbits/s over 82 km and at 420 Mbits/s over 203 km confirmed that the HRO-DFB laser is an excellent a single-frequency optical source for use in optical communication applications.     

V-grooved substrate buried heterostructure InGaAsP/InP laser emitting at 1.3 µm wavelength

Details of the fabrication, optimization of the dimensions of the active region, characteristics, and the aging results of theV- grooved substrate buried heterostructure (VSB) InGaAsP/InP laser are described. It is shown that the VSB laser can be fabricated in one-step epitaxy as well as two-step epitaxy. The active region width below 2.5 μm and the thickness of0.15-0.2 mum are shown to give stable fundamental mode operation and good temperature characteristics. The fundamental mode operation up to the optical output of 20 mW/facet at 25°C and the CW operation above 100°C are obtained. The pulse response showed the strongly damped relaxation oscillation with a frequency as high as 4.5 GHz. The spectral width under the modulation of 400 Mbit/s RZ single is as narrow as 25 Å in full width at half maximum. Highly stable aging characteristics at an elevated temperature of 50°C are obtained in both two-step epitaxy lasers and one-step epitaxy lasers.     

Transverse mode controlled in inGaAsP inP lasers at 1.5 µm range with buffer-layer loaded piano-convex waveguide (BL-PCW) structures

A modified plano-convex waveguide structure is studied analytically and successfully applied to InGaAsP/InP lasers in the1.5- 1.6 mum wavelength region to realize stable transverse mode operation. The structure of these lasers is characterized by a standard buffer layer between an active layer and an upper cladding layer and a waveguide layer of varying thickness between the active layer and the substrate. A theoretical analysis of this structure showed that, for a given channel depth, increases in buffer-layer thickness give rise to larger maximum channel widths of the substrate for fundamental transverse mode operation. It was also shown that the optical confinement factor in the active layer decreases little as the buffer-layer thickness is increased from 0.1 to 0.3 μm. Buffer-layer loaded plano-convex waveguide lasers in the 1.5 μm range were prepared by liquid phase epitaxy and fundamental transverse mode operation up untilI = 2I_{th}was obtained. The dc threshold current was 100-300 mA and the differential quantum efficiency per facet was 10-15 percent. Continuous CW operation for over 2000 h at 25°C has been achieved.     

High-power laser diodes based on asymmetric separate-confinement heterostructures

Asymmetric separate-confinement laser heterostructures with ultrawide waveguides based on AlGaAs/GaAs/InGaAs solid solutions, with an emission wavelength of ～1080 nm, are grown by MOCVD. The optical and electrical properties of mesa-stripe lasers with a stripe width of ～100 μm are studied. Lasers based on asymmetric heterostructures with ultrawide (>1 μm) waveguides demonstrate lasing in the fundamental transverse mode with an internal optical loss of as low as 0.34 cm^?1. In laser diodes with a cavity length of more than 3 mm, the thermal resistance is reduced to 2°C/W, and the characteristic temperature T ₀= 10°C is obtained in the range 0–100°C. A record-breaking wallplug efficiency of 74% and an output optical power of 16 W are reached in CW mode. Mean-time-between-failures testing for 1000 h at 65°C with an operation power of 3–4 W results in the power decreasing by 3–7%.     

Embedded-stripe GaAs-GaAlAs double-heterostructure lasers with polycrystalline GaAsP layers--I: Lasers with cleaved mirrors

We report a new type of embedded stripe laser in which low-order mode CW oscillation is successfully attained at room temperature. In order to achieve lateral current confinement, a high-resistivity polycrystalline GaAsP layer is formed around the mesa stripe by selective vapor-phase growth technology. It turns out that a stable single-mode operation is attained at an injected current up to several times the threshold value.     

Room temperature continuous wave operation of 671 nm wavelengthGaInAsP/AlGaAs VSIS lasers

Room-temperature continuous-wave (CW) operation of a liquid-phase epitaxy (LPE)-grown GaInAsP/AlGaAs laser that uses a V-channel substrate inner stripe (VSIS) structure to obtain current confinement and transverse mode control is discussed. The threshold current and lasing wavelength were 77 mA and 671 nm, respectively, and the temperature dependence of the threshold current was such that the characteristic temperature was 75 K     

Low threshold operation of 1.5-µm DFB laser diodes

Highly reliable distributed feedback (DFB) laser diodes operating at 1.5-μm wavelength range are fabricated through optimizing the device parameters. Thickness control of the active layer is found to be an essential factor in achieving low threshold operation of DFB lasers. The threshold current as low as 11 mA and stable single longitudinal mode CW operation up to 106°C is achieved with these DFB lasers.