D. P. Wilt

Monolithic hybrid mode‐locked 1.3 μm semiconductor lasers

We describe the first results of hybrid mode locking combining both active and passive mode locking of a semiconductor laser. These functions are integrated into a monolithic device with a 1.3 μm GaInAsP gain region, an active waveguide, and a saturable absorber. The devices have low threshold currents, and exhibit hysteresis in their light/current characteristics. The long integrated waveguides allow mode locking at a repetition rate of 15 GHz without the need for an external cavity. Pulse widths as short as 1.4 ps have been demonstrated using the combined effects of active and passive mode locking.

High‐frequency constricted mesa lasers

InGaAsP cw constricted mesa lasers at 1.3 μm are described which have a small‐signal 3‐dB bandwidth of 20 GHz at −70 °C. Large‐signal pseudorandom modulation at 8 Gb/s resulted in 100% optical modulation. The lasers were gain switched at 12 GHz with 100% optical modulation.

Channeled substrate buried heterostructure InGaAsP/InP laser employing a buried Fe ion implant for current confinement

A channeled substrate buried heterostructure InGaAsP/InP laser is demonstrated using a hybrid technique of Fe ion implantation followed by liquid phase epitaxy. A high resistivity region is formed by the implantation and subsequent anneal of Fe into an n‐type InP substrate, and this is used to provide a self‐aligned current confinement barrier layer. The use of an in situ anneal prior to liquid phase epitaxy minimizes the number of processing steps. Pulsed threshold currents as low as 22 mA have been achieved on devices utilizing broad area metal contacts.

Cleaved‐coupled‐cavity lasers with large cavity length ratios for enhanced stability

The fabrication and operation of the first cleaved‐coupled‐cavity (C3) semiconductor lasers with large cavity length ratios are described. The internal cleaved facet is precisely positioned by photochemically etching a groove through most of the wafer. Single longitudinal mode operation is obtained over a temperature range of 21 °C and over a current range of threshold to greater than four times threshold. Sidemode suppression of 100:1 was measured when the laser was modulated at 350 MHz with an extinction ratio greater than 10:1. These results are experimentally and theoretically compared to approximately equal length C3 lasers.

Effect of photocarrier spreading on the photoluminescence of double heterostructure material

Lateral spreading of photoexcited carriers can suppress the photoluminescence signal from double heterostructure wafers containing a p‐n junction independently from saturable defects in the material. Experimental results are presented and a theory is derived to show that in any double heterostructure with a p‐n junction the photoluminescence is suppressed if the power of the excitation source does not exceed a threshold value. The threshold power has been calculated in terms of material parameters, in excellent agreement with experimental results. This effect is the basis of a novel technique used for a nondestructive optical determination of the p‐clad layer sheet conductance as well as junction misplacement in double heterostructures, both of which are important parameters for injection lasers.

Improved linearity and kink criteria for 1.3‐μm InGaAsP‐InP channeled substrate buried heterostructure lasers

Nonlinearities or kinks in the light‐current characteristics of channeled substrate buried heterostructure lasers are associated with higher order transverse mode transition and lateral mode movement. The active area has been reduced to stabilize the transverse mode. Fundamental mode operation up to high powers (24 mW/facet) has been obtained in devices with threshold current as low as 15 mA. Measurements and calculations are presented which show that nonlinearities occur at higher output power in lasers with reduced active area.

1.5‐μm GaInAsP planar buried heterostructure lasers grown using chemical‐beam‐epitaxial base structures

GaInAsP/InP double heterostructures grown by chemical‐beam epitaxy have been used in conjunction with liquid‐phase‐epitaxial regrowth to fabricate high‐performance buried heterostructure lasers operating at a wavelength of 1.5 μm. These lasers show room‐temperature threshold currents as low as 12 mA, external quantum efficiencies as high as 0.2 mW/mA per facet, and, in general, linear output power up to ∼10 mW/facet. The 3‐dB bandwidth at optimal biasing is about 8 GHz and is believed to be limited by the heatsink stud. The relative intensity noise is low, <−150 dB/Hz at 1 GHz for bias currents from 50 mA to above 150 mA.

Etching of deep grooves for the precise positioning of cleaves in semiconductor lasers

Photoelectrochemical etching of InP is used to etch deep (80 μm), narrow (20 μm) grooves. The grooves are used to precisely position cleaves in semiconductor lasers and to demonstrate the first wafer processing of long/short cleaved‐coupled‐cavity (C3) lasers. Large numbers of low threshold C3 lasers wth very similar cavity lengths were obtained.

V‐groove distributed feedback laser for 1.3–1.55 μm operation

We describe a V‐groove distributed feedback laser operating at λ=1.5 μm. A second‐order diffraction grating has been defined by electron beam writing and transferred using ion beam milling after the crystal growth was completed. A single longitudinal mode operation with a mode rejection ratio larger than 5000:1 has been obtained under modulation rate of 1 GHz. The techniques used in this work can be applied to other types of buried heterostructure lasers.

Stop‐cleaved InGaAsP laser monolithically integrated with a monitoring detector

We report the monolithic fabrication of a stop‐cleaved laser with a monitoring detector. Stop‐cleaved, double channel planar buried heterostructure lasers with threshold currents of 57 mA have been obtained emitting at 1.3‐μm wavelength. For the monitoring detector on the same substrate we have estimated a quantum efficiency of 31% from the measured responsivity of 14.4 μA/mW and the theoretical diffraction coupling efficiency.