T. Cella

High‐gain InGaAsP‐InP heterojunction phototransistors

InGaAsP‐InP heterojunction phototransistors have been fabricated by liquid phase epitaxy. The phototransistors have optical gains greater than 100 for 1.26‐μm radiation. High internal current gains (≳300) have been achieved. Phototransistor relative spectral response has been measured for wavelengths in the range 0.7–1.5 μm.

High‐output power InGaAsP (λ=1.3 μm) strip‐buried heterostructure lasers

An InGaAsP (λ=1.3 μm) strip‐buried heterostructure laser with active layer strip widths of 5 μm is described. These devices show stable fundamental‐transverse‐mode operation with linear light‐current characteristics to pulsed output powers over 100 mW. Output powers as high as 500 mW are observed without catastrophic damage, which corresponds to twice the power output at which catastrophic mirror damage occurs for similar GaAlAs SBH lasers. Far‐field beam divergence is approximately 10° and 30° in the directions parallel and perpendicular to the junction, respectively. cw operation with a threshold current of 170 mA has been achieved at room temperature.

Electronically tunable distributed feedback lasers

The fabrication and performance characteristics of frequency tunable two‐section distributed feedback lasers are reported. The lasers are of the double channel planar buried heterostructure type and utilize a second order grating for frequency selective feedback. The laser emits in a single frequency with a cw linewidth of ∼50 MHz. The single frequency output can be tuned by ∼2 A by varying the current through one of the two sections. Electronically tunable sources of this type are potentially useful for coherent fiber transmission systems.

Integrated external cavity laser

The fabrication and performance characteristics of single frequency integrated external cavity lasers of the coupled cavity type and the distributed Bragg reflector type are described. The active cavity section of these devices utilizes the double channel planar buried heterostructure scheme for current confinement. The lasers emit near 1.55 μm. The threshold current of these lasers is in the range 70–120 mA. cw linewidth of 7 MHz has been obtained for a 2‐mm‐long laser at an output power of 3 mW. We believe lasers with longer external cavity should exhibit lower cw linewidths.

InGaAsP laser with semi‐insulating current confining layers

The fabrication and performance characteristics of a InGaAsP laser structure with semi‐insulating current confining layers are reported. The semi‐insulating layers are Fe‐doped InP and are grown using the metalorganic chemical vapor deposition growth technique. The lasers have threshold currents in the range 20–30 mA and external differential quantum efficiency ∼0.2 mW/mA/facet at 30 °C. The bandwidth for small‐signal response is ∼2 GHz which suggests that the laser structure is suitable for high bit rate lightwave transmission systems. Initial aging results yield an estimated operating lifetime of 10 years at 20 °C.

Monolithically integrated thermoelectric controlled laser diode

The fabrication and performance characteristics of a monolithically integrated thermoelectric controlled laser diode are described. The thermoelectric element is the n‐InP substrate. The lasers (λ∼1.51 μm InGaAsP) have threshold currents of ∼20 mA and operate kink free to >10 mW/facet. A variation of active region temperature of ± 2.5 °C has been achieved using 50 mA of thermoelectric controller current. The observed frequency tuning rate associated with this temperature shift is ∼0.5 GHz/mA. The device is useful for applications that require a high degree of frequency stability or small frequency tuning. Some potential lightwave system applications are in single‐frequency transmission systems, coherent transmission systems, optical amplifiers, resonant external cavity modulators, and injection locking.

InGaAsP double heterostructure lasers (λ=1.3 μm) with etched reflectors

Discrete InGaAsP double heterostructure lasers (λ=1.3 μm) have been fabricated by a novel batch process which incorporates chemically etched end reflectors. The etched‐mirror lasers have threshold current densities as low as 3.5 kA/cm2. The average threshold current density for the etched‐mirror lasers is approxiamtely 40% higher than for standard cleaved‐mirror devices fabricated from the same wafer. The laser fabrication process permits batch fabrication of a much wider variety of discrete laser geometries than conventional laser‐cleaving techniques.

1.3 mu m semiconductor laser power amplifier

The performance of a 3.4-Gb/s system using a low-power 1.318- mu m distributed-feedback (DFB) laser transmitter and a traveling-wave semiconductor laser power amplifier is studied. The -14.5-dBm, input from a directly modulated DFB laser is boosted to +10.3 dBm, of which +4.8 dBm is coupled into the transmission fiber. The penalty, caused by amplifier noise and pattern effects due to gain saturation, is less than 0.5 dB.<<ETX>>

InGaAsP closely spaced dual wavelength laser

The fabrication and performance characteristics of an independently controllable closely spaced dual wavelength laser structure are described. The laser structure utilizes semi‐insulating (Fe‐doped InP) layers both for confinement of the current to the active regions and for separation of the active regions of the two lasers. Both lasers emit in single frequencies near 1.55 μm by virtue of frequency selective feedback provided by a second order grating. The light coupled into a single mode fiber from both lasers is about 5 dB smaller than that for optimum coupling arrangement of each laser. Dual wavelength laser structures of this type are useful for wavelength multiplexed optical transmission systems.

High‐power gain‐guided InGaAsP laser array

We have fabricated InGaAsP gain‐guided laser arrays emitting at 1.3 μm. These devices have threshold currents in the range 300–400 mA at 30 °C and have been operated to pulsed output powers as high as 400 mW. More than 100 mW of output power has been obtained up to an ambient temperature of 60 °C. The lasers emit in multilongitudinal modes with a far‐field divergence of 20°×35°. A gain‐guided InGaAsP laser array of the type described here can be used in some applications requiring high‐power lasers emitting at 1.3 μm.