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.     

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.     

Regimes of feedback effects in 1.5-µm distributed feedback lasers

We have measured the effects of feedback on the spectra of 1.5-μm DFB lasers from feedback power ratios as low as -80 dB up to -8 dB. Five distinct regimes of effects are observed with well defined transitions between them. The dependence of these effects on the distance to the reflection is also investigated.     

Distributed feedback InGaAsP/InP lasers with window region emitting at 1.5 µm range

Distributed feedback (DFB) InGaAsP/InP lasers with a window region formed at an end of the corrugated DFB region were made in order to overcome the problems inherent in the previous structures of DFB lasers with cleaved, sawed, etched, or AR-coated facets, or with an unexcited corrugation region. The window structure DFB lasers showed linear current versus output (I-L) curves, in contrast to those with a hysteresis or a kink appearing in a DFB laser with an unexcited region. Suppression of Fabry-Perot (F-P) resonances due to the two facets were sufficient enough to keep a single longitudinal mode property by DFB up to high excitation level. CW operation up to 65°C was achieved at the 1.5 μm wavelength range. Axial modes concerning the corrugated resonator were measured at about the threshold current. A stop band of a DFB laser was clearly observed with two dominant modes and much smaller submodes, which almost agreed with the axial modes predicted from a basic DFB theory.     

Spectral linewidth estimation of a 1.5 µm range InGaAsP/InP distributed feedback laser

Spectral linewidth of a 1.5 μm range distributed feedback buried heterostructure (DFB-BH) laser in CW operation is estimated theoretically and experimentally. Considering the equivalent mirror facet loss coefficient and the confinement factor in the active layer, etc., we modified the conventional formula for the spectral linewidth of single-mode semiconductor lasers and presented a formula for the linewidth of DFB lasers. Furthermore, power-dependent linewidth measurements of a 1.5 μm range InGaAsP/InP DFB-BH laser with a window region were carried out using Fabry-Perot interferometers. The linewidth was observed to increase linearly with inverse output power. The measured result was explained by the calculated result through the modified formula. The full width at half maximum was estimated to be 50 MHz at an output power of 1 mW.     

1.5-1.6 µm GaInAsP/InP dynamic-single-mode (DSM) lasers with distributed Bragg reflector

The theoretical bases and the experimental results of the dynamic behavior of1.5-1.6 mum GaInAsP/InP dynamic-single-mode (DSM) lasers with distributed Bragg reflector (DBR) are given. A condition for the single-mode operation of a rapidly modulated DBR laser, called a "dynamic-single-mode laser," and the dynamic spectral width were theoretically presented. Experimentally, buried-heterostructure distributed-Bragg-reflector integrated-twin-guide (BH-DBR-ITG) and buried-heterostructure butt-jointed-built-in distributed-Bragg-reflector (BH-BJB-DBR) lasers emitting at the wavelength of1.5-1.6 mum were directly modulated up to 3 GHz, and the stable single-mode operations were obtained in both types of lasers. The dynamic spectral width at the worst modulation condition was measured to be 0.27 nm, which was aboutfrac{1}{35}times smaller than that of conventional lasers.     

InGaAsP ridge waveguide distributed feedback lasers operating near 1.55 µm

Fabrication and performance of ridge waveguide distributed feedback lasers grown by liquid phase epitaxy for operation in the 1.50-1.58 μm spectral region have been studied. These lasers incorporate first- and second-order diffraction gratings written by the electron beam lithography and optical holography and defined by wet chemical etching and novel ion-beam-milling techniques. Ridge waveguides were formed by post-regrowth processing and heteroepitaxial ridge overgrowth. Distributed feedback ridge lasers were characterized by room temperature CW threshold currents as low as 40 mA, two facet external quantum efficiencies of up to 40 percent and stable transverse mode operation up to the output power of 10 mW. In strongly coupled devices, even with a cleaved resonator, the Bragg mode intensity exceeds that of the residual Fabry-Perot modes by a factor of 4000:1. Stable, single longitudinal mode operation was obtained under modulation rates as high as 4 GHz and error free transmission experiments over 60-km lengths of single mode fiber reproducibly performed at data rates as high as 2 Gbit/s.     

1.5-µm λ/4-shifted InGaAsP/InP DFB lasers

A single wavelength light source in 1.5-μm range was developed using InGaAsP/InPlambda/4-shifted distributed feedback (DFB) semiconductor heterostructures. Superiority of thelambda/4-shifted DFB structure in terms of stability of the main mode at the Bragg wavelength was shown theoretically, in which the threshold, the output, and the polarization characteristics were taken into account. Alambda/4-shifted corrugated grating was made by a newly developed negative and positive photoresists technique. Buried heterostructure (BH) diode lasers with nonreflective window ends were fabricated and highly stable single-mode operation with a low threshold was obtained reproducibly. Direct modulation properties and life-tests results indicated that thelambda/4-shifted DFB lasers could be a reliable single-mode light source in a long span lightwave transmission system in 1.5-μm range.     

Spectral behavior of 1.5 µm BIG-DBR-DSM lasers

Direct modulation properties of BIG-DBR-DSM lasers were investigated by measuring both the time-averaged and the time-resolved spectra. A high side-mode-suppression ratio of more than 30 dB was obtained from time-averaged measurements with the modulation frequency in the range of 250 MHz-2 GHz. The dynamic wavelength shift at - 3 dB level obtained from both time-averaged and time-resolved measurements was less than 2 Å. Time-resolved measurements showing an oscillatory behavior of the dynamic wavelength shift with both red and blue shifts were also observed. Calculations based on a numerical solution of the rate equations, which agreed quantitatively with the measurement, indicate a line width enhancement factor estimated to lie between 3.5 and 5.5.     

Lasing characteristics of 1.5 - 1.6 µm GaInAsP/InP integrated twin-guide lasers with first-order distributed Bragg reflectors

Lasing characteristics of1.5-1.6 mum GaInAsP/InP integrated twin-guide lasers with first-order distributed Bragg reflectors (DBR-ITG lasers) are given theoretically and experimentally. At this wavelength region the fiber loss is ultimately low, but the effect of the material dispersion is serious. It is theoretically found that single longitudinal mode operation over twice the threshold current is obtainable with high quantum efficiency by optimizing the coupling properties and configurational parameters of the DBR-ITG laser. The experimental results are also demonstrated. Single longitudinal mode operation of1.5-1.6mum DBR-ITG lasers under high-speed direct modulation was achieved with a pulsewidth of 1.5 ns.     

Effect of mirror facets on lasing characteristics of distributed feedback InGaAsP/InP laser diodes at 1.5 µm range

The effect of mirror facets on lasing properties of distributed feedback (DFB) InGaAsP/InP laser diodes was studied theoretically and experimentally. A DFB laser with a window region was found to be suitable to examine the effect of mirror facets. The effective reflectivity of a window structure was calculated to be very small, typically as small as 0.03 percent for a few tens of micrometers of the window region. These small effective reflectivities were experimentally confirmed. Three kinds of DFB lasers, i.e., a double-window (DW), a single-window (SW), and a Fabry-Perot (FP), were discussed. Two modes with a separation corresponding to a so-called stopband appeared in a DW-DFB laser, in which almost no reflection at both ends was estimated. On the other hand, the threshold and the resonant wavelength of an SW- and an FP-DFB laser were found to be sensitive to the phases of corrugation at the facets. It turned out, however, that the mirror facet contributed to the single-mode operation due to an asymmetric resonant spectrum and to the reduction in the threshold. Although a low-threshold-current FP-DFB laser was experimentally obtained, the coincidence between the gain peak and the Bragg wavelengths was essential in this type. The SW-DFB laser seemed the most promising among the three types in terms of the stability of the single-mode operation.     

Laterally coupled InGaAsP/InP distributed feedback lasers at 1.5μm for chemical sensing applications

Data is presented on stable, tunable single-mode operation from laterally coupled InGaAsP/InP ridge waveguide distributed feedback lasers at ~1.5 μm, suitable for chemical sensing, realised by a greatly simplified fabrication process requiring a single MOCVD growth step. Completed lasers show sidemode suppression ratios as high as 47 dB and wavelength shifts with injection current of 0.035 nm/mA (or 4.5 GHz/mA)     

Static characteristics of 1.5 - 1.6 µm GaInAsP/InP buried heterostructure butt-jointed built-in integrated lasers

Lasing characteristics of GaInAsP/InP buried heterostructure butt-jointed built-in distributed Bragg reflector integrated lasers (BH-BJB-DBR lasers) intended for dynamic single mode operation in the wavelength range of1.5-1.6 mum are given. In the first section, the coupling property between the active region and the butt-jointed external waveguide region is calculated to show the possibility of large fabrication tolerance. A coupling coefficient of more than 95 percent is estimated. Secondly, the GaInAsP/InP integrated lasers were fabricated and tested in the view of the static characteristics and the axial mode selection property. Lateral mode control was achieved by the use of a buried heterostructure, so that the axial and lateral modes were maintained to a fixed single mode. The lasers thus fabricated were operated in CW conditions at room temperature with a threshold current of about 100 mA. Single longitudinal mode operation was observed with a temperature dependence of about 0.13 nm/deg with the temperature range of more than50-65degC at around 0°C. Differential quantum efficiency as high as 13 percent/ facet was obtained for the laser with power output of more than 5 mW/facet. The output spectrum below threshold indicated the strong wavelength selectivity of the DBR region, and the net gain difference between the main DBR mode and the adjacent submode was measured to be about 6 cm^-1. No appreciable degradation and change of characteristics have been observed even after CW operation of more than 9770 h at 20°C.     

Reliability in InGaAsP/InP buried heterostructure 1.3 µm lasers

A study was conducted of aging-induced Sn whisker growth at the surface of Au-Sn bonding solder layers around a laser chip, as well as metallurgical reactions, especially in p-side down lasers, at the interface of the solder and laser crystal just below the active layer. These phenomena cause electrical shorts in InGaAsP/InP laser diodes, which occur suddenly in devices operated for long periods without any previous symptoms having appeared in their aging characteristics. To completely eliminate such failures, a novel assembling method in which chips were mounted p-side up on semiinsulating SiC submounts using Pb-Sn solder, was applied to InGaAsP/InP buried heterostructure (BH) lasers emitting at 1.3 μm. BH lasers assembled by this method do not suffer any shorting failure even after 8000 h operation under 60°C and 5 mW/facet output conditions. The small degradation rates obtained, for example, 3 percent/kh (median) at 60°C, certify the reliability of these improved lasers. As long as the stripe width of the active layer was optimized to be in the range of1.5-2.5 mum necessary for obtaining kink-free light output versus current properties, no detrimental changes in laser characteristics, including transverse and longitudinal modes and dynamic output response, were observed in aged lasers. In this paper, the long-term degradation modes observed are presented, and possible causes are discussed.     

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.     

Narrow-linewidth strained-layer 1.5 mu m multiquantum well distributed feedback lasers

The performance characteristics of narrow-linewidth strained-layer 1.5 mu m multi-quantum-well distributed feedback (MQW-DFB) lasers are presented. Measured linewidth as low as 3.5 MHz has been observed for one of the 250 mu m long devices at 14.4 mW output. Under 1.7 Gbit/s 1.0, 1.0, . . . pattern signal modulation, the lasers have 20 dB down full width chirp in the range of 5-6 AA for the off state at 0.8 I/sub th/. The chirp widths are about half of those of bulk-active DFB lasers. A 1.7 Gbit/s amplitude-shift-keying transmission experiment using one of the low-chirp lasers has been demonstrated. The transmission over 60 km of standard fibre only result in a 0.8 dB dispersion power penalty and has a receiver sensitivity of -36.2 dBm at BER=10/sup -9/.<>     

New 1.5 ?m wavelength GaInAsp/InP distributed feedback laser

A new 1.5 ?m-wavelength GalnAsP/InP distributed feedback buried-heterostructure laser was fabricated by a three-step LPE growth process. The second-order corrugation grating was formed on the waveguide layer grown on the active layer. High differential quantum efficiency of 13%/facet was obtained. Single-longitudinal-mode operation in the temperature range from ?20°C to 55°C was obtained.     

1.5 ?m region InP/GaInAsP buried heterostructure lasers on semi-insulating substrates

InP/GaInAsP buried heterostructure (BH) lasers for the 1.5 ?m region have been fabricated on semi-insulating InP substrates. The threshold current of the lasers is as low as 38 mA under CW operation at 25°C, which is nearly the same as for BH lasers fabricated on n-type InP substrates.