Strain-compensated 1.3-μm AlGaInAs quantum-well lasers withmultiquantum barriers at the cladding layers

Strain-compensated 1.3-μm AlGaInAs graded-index separate confinement heterostructure (GRINSCH) lasers with multiquantum barrier (MQB) at both the nand p-cladding layers are comprehensively studied and compared with the conventional GRINSCH lasers. It is found that the lasers with MQBs exhibit lower threshold current, higher maximum output power and better temperature characteristics because of the enhanced barrier height for carrier leakage. The characteristic temperature is improved as much as 10 K and the vertical far-field angle is also reduced from 38° to 32° as compared to the conventional counterpart     

1.3-μm AlGaInAs buried-heterostructure lasers

1.3-μm AlGaInAs-InP strained multiple-quantumwell (MQW) buried-heterostructure (BH) lasers have been successfully fabricated. InP current blocking layers could be smoothly regrown using the simple HF pretreatment, although the etched active region includes Al-containing layers. The threshold current I_th was typically 11 mA for as-cleaved 350-μm-long devices, which is about 30% lower than that of the ridge laser counterparts. A maximum continuous-wave operating temperature as high as 155°C was achieved. For the 200-μm-long device with the high-reflective-coated rear-facet, I_th was as low as 7.5 mA and characteristic temperature T₀ was 80 K. The BH lasers also provided more circular far-field patterns and lower thermal resistances than for ridge lasers     

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     

1.3-μm GaInNAs-AlGaAs distributed feedback lasers

Room temperature continuous-wave operation of 1.3-μm single-mode GaInNAs-AlGaAs distributed feedback (DFB)-lasers has been realized. The laser structure has been grown by solid source molecular beam epitaxy (MBE) using an electron cyclotron resonance plasma source for nitrogen activation (ECR-MBE). Laterally to the laser ridge a metal grating is patterned in order to obtain DFB. The evanescent field of the laser mode couples to the grating resulting in single-mode DFB emission. The continuous wave threshold currents are around 120 mA for a cavity with 800-μm length and 2 μm width. Monomode emission with side-mode suppression ratios of nearly 40 dB have been obtained     

1.3-μm P-i-N photodetector using GaAs with As precipitates(GaAs:As)

The fabrication of a GaAs detector which operates in the 1.3- to 1.5-μm optical range is reported. The detector is a P-i-N photodiode with an intrinsic layer composed of undoped GaAs which was grown at 225°C and subsequently annealed at 600°C. This growth process has been demonstrated to produce a high density of As precipitates in the low-temperature grown region, which the authors show to exhibit absorption through internal photoemission. The internal Schottky barrier height of the As precipitates is found to be 0.7 eV, leading to reasonable room-temperature responsivity out to around 1.7 μm     

Temperature dependence of lasing characteristics forlong-wavelength (1.3-μm) GaAs-based quantum-dot lasers

Data are presented on the temperature dependence of 1.3-μm wavelength quantum-dot (QD) lasers. A low-threshold current density of 90 A/cm² is achieved at room temperature using high reflectivity coatings. Despite the low-threshold current density, lasing at the higher temperatures is limited by nonradiative recombination with a rapid increase in threshold current occurring above ~225 K. Our results suggest that very low threshold current density (⩽20 A/cm ²) can be achieved at room temperature from 1.3-μm QD lasers, once nonradiative recombination is eliminated     

High-reliability 1.3-μm InP-based uncooled lasers in nonhermeticpackages

We report the first uncooled nonhermetic 1.3-μm InP-based communication lasers that have reliability comparable to their hermetically packaged counterparts for possible applications in fiber in the loop and cable TV. The development of reliable nonhermetic semiconductor lasers would not only lead to the elimination of the costs specifically associated with hermetic packaging but also lead the way for possible revolutionary low-cost optoelectronic packaging technologies. We have used Fabry-Perot capped mesa buried-heterostructure (CMBH) uncooled lasers with both bulk and MQW active regions grown on n-type InP substrates by VPE and MOCVD. We find that the proper dielectric facet passivation is the key to obtain high reliability in a nonhermetic environment. The passivation protects the laser from the ambient and maintains the proper facet reflectivity to achieve desired laser characteristics. The SiO facet passivation formed by molecular beam deposition (MBD) has resulted in lasers with lifetimes well in excess of the reliability goal of 3,000 hours of operation at 85°C/90% RH/30 mA aging condition. Based on extrapolations derived experimentally, we calculate a 15-year-average device hazard rate of <300 FITs (as against the desired 1,500 FITs) for the combination of thermal-and humidity-induced degradation at an ambient condition of 45°C/50% RH. For comparison, the average hazard rate at 45°C and 15 years of service is approximately 250 FITs for hermetic lasers of similar construction. A comparison of the thermal-only degradation (hermetic) to the thermal plus humidity-induced degradation (nonhermetic) indicates that the reliability of these nonhermetic lasers is controlled by thermal degradation only and not by moisture-induced degradation. In addition to device passivation for a nonhermetic environment, MBD-SiO maintains the optical, electrical, and mechanical properties needed for high-performance laser systems     

Continuously tunable photopumped 1.3-μm fiber Fabry-Perotsurface-emitting lasers

Continuously tunable, single-frequency, optically pumped semiconductor-fiber lasers are demonstrated that embody a half-cavity, vertical-cavity surface-emitting laser within a fiber Fabry-Perot cavity. Continuous wavelength tuning over 40 nm at 1300-nm wavelength region is obtained under continuous-wave operation     

High-temperature operating 1.3-μm quantum-dot lasers fortelecommunication applications

High-performance 1.3-μm-emitting quantum-dot lasers were fabricated by self-organized growth of InAs dots embedded in GaInAs quantum wells. The influence of the number of quantum-dot layers on the device performance was investigated. Best device results were achieved with six-dot layers. From the length dependence; a maximum ground state gain of 17 cm^-1 for six dot layers could be determined. Ridge waveguide lasers with a cavity length of 400 μm and high-reflection coatings show threshold currents of 6 mA and output powers of more than 5 mV. Unmounted devices can be operated in continuous wave mode up to 85°C. A maximum operating temperature of 160°C was achieved in pulsed operation for an uncoated 2.5-mm-long ridge waveguide laser     

1.3-μm AlGaInAs-InP buried-heterostructure lasers with modeprofile converter

AlGaInAs buried-heterostructure (BH) lasers with a mode profile converter (MPC) have been successfully fabricated for the first time. The thickness of the multiple-quantum-well (MQW) waveguide was vertically tapered by selective area growth (SAG). The threshold current I_th was 14.6 mA with a 600-μm-long cavity and a high-reflective-coated rear facet. The full-width at half-maximum of the far-field pattern in the perpendicular and horizontal directions were 9.2° and 12.6°, respectively. The optical coupling loss between lasers with MPC and a single-mode fiber was 3.0 dB when the distance between the laser and fiber was 20 μm     

High-temperature characteristics of 1.3-μm InAsP-InAlGaAs ridgewaveguide lasers

High-temperature characteristics of InAsP-InAlGaAs strained multiquantum-well (MQW) lasers with a large conduction band discontinuity (ΔE_c) are demonstrated. The InAsP-InAlGaAs MQW ridge waveguide lasers with narrow stripes exhibited a characteristic temperature as high as 143 K in the range from 25°C to 85°C. This material system is promising for developing a cooling-system-free 1.3-μm laser     

Characteristics of 1.3-μm InGaAsP lasers used as photodetectors

The photodetection capabilities of 1.3-μm channel substrate lasers are studied. The diodes can be used either as lasers or detectors in single-mode-fiber half-duplex communication links. As a detector, a responsivity of 0.26 A/W is obtained by efficiently coupling the input radiation into the facet using a lensed single-mode fiber. The spectral bandwidth extends from 1.1 to 1.37 μm. The dark current at room temperature is 200 nA at 1-V bias and due in part to current leakage through the Fe-doped InP blocking layer. As lasers, the diodes have a frequency response of 4 GHz, and as detectors, the 3-dB bandwidth is 600 MHz     

Design criteria of 1.3-μm multiple-quantum-well lasers forhigh-temperature operation

We present design criteria for high-temperature operation in 1.3-μm multiple-quantum-well (MQW) lasers from the viewpoint of the light output power penalty, i.e., the change in the light output power at a fixed drive current with increasing temperature. It is shown that not only the characteristic temperature (T₀) but also internal loss dependence on temperature (γ) and threshold current (I_th) are significant parameters for reducing the power penalty. We compare the high-temperature performance of InGaAsP-based and AlGaInAs-based MQW lasers and demonstrate that AlGaInAs-based lasers have more potential in terms of the power penalty. Furthermore, we also demonstrate that the power penalty can be reduced by introducing a buried-heterostructure (BH) structure into AlGaInAs-based lasers. From these results, we conclude that the AlGaInAs-based BH lasers are promising for high-temperature performance     

High-temperature single-mode operation of 1.3-μm strained MQWgain-coupled DFB lasers

Single-mode and high-power operation at temperatures up to 120°C has been achieved in 1.3-μm strained MQW gain-coupled DFB lasers. A stable lasing wavelength is maintained due to a large modal facet loss difference of the two Bragg modes, which is provided by the gain-coupling effect. A very low temperature dependence of the threshold current has been obtained by detuning the lasing wavelength to the long wavelength side of the material gain peak at room temperature, which effectively compensates the waveguide loss at higher temperatures. An infinite characteristic temperature T_o can be realized at certain ranges of temperature depending on the detuning value     

Observation of degradation recovery in 1.3-μm GaInAsP-InPinverted-rib semiconductor lasers

This paper reports some effects arising from interrupted lifetest of 1.3-μm GaInAsP-InP inverted-rib laser diodes. This unconventional lifetest method involves constant power biasing at 4 mW/facet and 8 mW/facet, respectively, at 50°C, followed by a period during which the devices were left unbiased at room temperature (off-test period). At the end of the off-test period, the devices were put back on constant power biasing at 50°C. A pronounced reduction in the threshold current, current for 4 mW/facet and 8 mW/facet were observed during the initial part of the off-test period. Similar improvements were also seen in the external quantum efficiency with corresponding variations also occurring in the device series resistance, characteristic temperature, threshold junction voltage, and the emission spectra linewidth. Such recovery effects have so far been observed to occur only in the GaInAsP-InP inverted-rib devices     

Low-threshold current, high-efficiency 1.3-μm wavelengthaluminum-free InGaAsN-based quantum-well lasers

We demonstrate high-performance Al-free InGaAsN-GaAs-InGaP-based long-wavelength quantum-well (QW) lasers grown on GaAs substrates by gas-source molecular beam epitaxy using a RF plasma nitrogen source. Continuous wave (CW) operation of InGaAsN-GaAs QW lasers is demonstrated at λ=1.3 μm at a threshold current density of only J_TH =1.32 kA/cm². These narrow ridge (W=8.5 μm) lasers also exhibit an internal loss of only 3.1 cm^-1 and an internal efficiency of 60%. Also, a characteristic temperature of T₀=150 K from 10°C to 60°C was measured, representing a significant improvement over conventional λ=1.3 μm InGaAsP-InP lasers. Under pulsed operation, a record high maximum operating temperature of 125°C and output powers greater than 300 mW (pulsed) and 120 mW (CW) were also achieved     

Theoretical study of the temperature dependence of 1.3-μmAlGaInAs-InP multiple-quantum-well lasers

The temperature dependence of the differential gain, carrier density, and transparency current density for 1.3-μm AlGaInAs-InP multiple-quantum-well lasers has been theoretically studied using the optical gain calculation from 250-380 K. The characteristic temperatures of the carrier density and differential gain at threshold are calculated to be 254 and 206 K, respectively. The Auger current density accounts for more than 50% of the total current density. The leakage current density exhibits the highest temperature sensitivity and becomes an essential part of the total current density at a high temperature. The calculated characteristic temperatures of the transparency and threshold current densities are 106 and 84 K, respectively, which agree well with the reported experimental results     

Well-thickness dependence of high-temperature characteristics in1.3-μm AlGaInAs-InP strained-multiple-quantum-well lasers

Well-thickness dependence of temperature characteristics of 1.3-μm AlGaInAs-InP strained-multiple-quantum-well lasers was investigated. Higher characteristic temperatures of threshold current density were obtained for thicker wells up to 6 nm. Fabricated ridge-waveguide lasers with 6-nm-thick wells exhibited characteristic temperature of as high as 125 K. Relaxation-oscillation frequency reduced by only 13% between 25°C and 85°C     

Design criteria for highly-efficient operation of 1.3-μmInP-based strained-layer multiple-quantum-well lasers at elevatedtemperatures

We derive a basic design rule for highly-efficient operation of 1.3-μm InP-based strained-layer (SL) multiple-quantum-well (MQW) lasers at elevated temperatures on the basis of a self-consistent numerical approach including the Poisson equation and effective-mass equations. Following the derived design rule, high-efficiency (0.55 W/A at 363 K) and high-power (over 35 mW at 363 K) InP-based SL-MQW lasers have been fabricated     

Calculated performances of 1.3-μm vertical-cavitysurface-emitting lasers on InGaAs ternary substrates

1.3-μm vertical-cavity surface-emitting lasers (VCSEL's) on InGaAs ternary substrates are proposed and designed, It is shown that a deep potential well on the ternary substrate enlarges optical gain of a strained quantum well in the wavelength region of 1.3 μm. A higher reflectivity distributed Bragg reflector (DBR) is also obtained by the use of the ternary substrate because materials with a large refractive-index difference can be used for the DBR. Calculated threshold current density of 1.3-μm VCSEL's on the ternary substrates is much lower than those on the conventional InP substrates. The possibility of extremely low threshold current density below 200 A/cm ² and temperature-insensitive operation are described