T. P. Lee

Bonding by atomic rearrangement of InP/InGaAsP 1.5 μm wavelength lasers on GaAs substrates

A technique, namely bonding by atomic rearrangement has been invented to realize high quality heteroepitaxy for lasers and optoelectronics. High performance lasers of 1.5 μm wavelength have been fabricated on GaAs substrates using this method. The laser has the same threshold current and quantum efficiency as lasers on InP substrates. No performance degradation has been observed. The transmission electron microscopic results show that the heteroepitaxy is excellent, without a single threading dislocation or stacking fault.

Wavelength-tunable and single-frequency semiconductor lasers for photonic communications networks

The present status of wavelength-tunable and single-frequency devices needed for the broadband integrated services digital network (BISDN) of the future is reviewed. The various systems applications and requirements and, in turn, the device parameters that are relevant to those requirements are described. The basic material and structural parameters of the lasers are discussed, and the fundamental operational principles are explained. Various single-frequency, high-speed, and tunable laser structures are reviewed, and their characteristics are presented.<<ETX>>

Very low threshold current density 1.5 μm GaInAs/AlGaInAs graded‐index separate‐confinement‐heterostructure strained quantum well laser diodes grown by organometallic chemical vapor deposition

Very low threshold current densities of 200 and 400 A/cm2 were obtained in 1.5 μm GaInAs/AlGaInAs tensile and compressive strained‐layer quantum well laser diodes (SL‐QW LDs), grown by organometallic chemical vapor deposition, with continuously graded‐index separate‐confinement‐heterostructure. The differential quantum efficiency of SL‐QW LDs showed less sensitive to temperature in contrast to that of a lattice matched QW LD. This is attributed to the decrease of intervalence band absorption due to the strain‐induced reduction in the valence band density of state. The polarization of output power for a tensile SL‐QW LD showed transverse magnetic (TM) mode, while that for a lattice matched and a compressive SL‐QW LDs showed transverse electric (TE) mode.

Analysis of origin of nonlinear gain in 1.5 μm semiconductor active layers by highly nondegenerate four‐wave mixing

The origin of the nonlinear gain effect in 1.5 μm semiconductor active layers is investigated by using highly nondegenerate four‐wave mixing, where the pump‐probe detuning is extended up to 2 THz. From the signal intensity measured as a function of the detuning frequency we find that both the spectral hole burning and the dynamic carrier heating contribute to the four‐wave mixing. The dynamic carrier heating, however, creates the index grating rather than the gain grating, and hence, the spectral hole burning is the main origin of the nonlinear gain effect.

Low‐threshold (≤ 92 A/cm2) 1.6 μm strained‐layer single quantum well laser diodes optically pumped by a 0.8 μm laser diode

To explore the ultimate threshold current limit in long‐wavelength semiconductor lasers, InxGa1−xAs/InP strained‐layer single quantum well laser diodes were studied for the first time by optically pumping with a 0.8 μm laser diode. Low‐threshold (≤92 A/cm2) cw operation was obtained and the lasing wavelength (1.62 μm) corresponding to the transition from the first quantization state of a 25 A In0.8Ga0.2As well was observed. By taking the carrier collection efficiency (≤77%) into account, the actual threshold current density could be as low as 70 A/cm2.

Effect of operating electric power on the dynamic behavior of quantum well vertical‐cavity surface‐emitting lasers

We investigated the effect of high operating voltage and series resistance on the dynamic behavior of strained InGaAs/GaAs quantum well vertical‐cavity surface‐emitting lasers (VCSELs). A large wavelength chirp in the lasing spectrum is observed for the lasers with high voltage/resistance even under low‐duty‐cycle pulse operation due to resistive heating close to the laser junction. Using an optimized laser design, VCSELs with 2.6 V threshold voltage and 40 Ω resistance are achieved. We believe this is the lowest threshold voltage and resistance reported to date for a 20 μm VCSEL with as‐grown mirrors. The wavelength chirp is reduced by nearly two orders of magnitude for these improved lasers.

High quality GaAs quantum well lasers grown on InP substrates by organometallic chemical vapor deposition

High quality GaAs quantum well lasers grown on (100) and 3°‐off (100)InP substrates by organometallic chemical vapor deposition were investigated for the first time. 50‐μm‐wide broad‐area gain‐guided lasers were fabricated using preferential proton implantation. Low threshold densities, 800 and 1080 A/cm2, were obtained at room temperature for lasers with 1.25‐mm‐long cavities grown on 3°‐off (100) and (100) oriented InP substrates, respectively. High quantum efficiency of 36% and nearly single longitudinal mode emission were also achieved from these lasers.

Novel etching technique for a buried heterostructure GaInAs/AlGaInAs quantum‐well laser diode

A novel etching technique for the 1.5‐μm GaInAs/AlGaInAs buried heterostructure quantum‐well laser diode is developed. Tartaric acid is used for the etching of GaInAs and AlGaInAs layers for the first time. Using a three‐step material‐selective etching, a 3‐μm‐high mesa with about 1.5‐μm‐wide active layer and 3‐μm‐wide contact layer can be achieved with good reproducibility. Nearly flat surfaces were obtained after a two‐step organometallic chemical vapor deposition growth. A low threshold current of 11 mA was obtained for a 570‐μm‐long cavity device.

Long-wavelength strained-layer quantum-well lasers

We have studied the effect of strain on the laser threshold current density in the 1.3 and 1.55 micrometers wavelength regions using both GaInAsP/InP and AlGaInAs/InP material systems. Low threshold current densities have been obtained for both compressive- and tensile-strained quantum well lasers. We have also fabricated 20-wavelength distributed-feedback laser arrays using both compressive- and tensile-strained quantum well active layers. A wide optical gain spectrum and a sub-MHz linewidth have been demonstrated.

Novel Optical Techniques For Characterization of Advanced Semiconductor Lasers For Telecommunications

We have witnessed a rapid advancement in optical fiber telecommunications in the last decade. The bit rate of early optical transmission systems in the late 1970s was 45 Mbit/s. By the m1d4980s, the transmission speed had been increased to rates ranging from 400 Mbitls to 560Mbit/s. More recently, SONET hierarchy, from OC- 1 , OC-3, OC-12, to OC-48 at 51.84 Mbitis, 1 55.52MbitJs, 622 Mbitls to 2.488 Gbitls respectively, has been the standard chosen by CCITT. The next SONET standard rate of OC-l92 at 10 Gbitis is now under consideration. Although laser transmitters at 10 Gbitls rate are still in the research and development stage, new products will be introduced in the marketplace to fuffill systems and networking needs in the near future. The singlemode optical fiber has a potential bandwidth of over 30 THz. In order to utilize this bandwidth, high density wavelength-division-multiplexing (WDM) has been considered. WDM can offer not only the increased usage of bandwidth, but also the flexibility of routing signals in a network by means of wavelength [11. In the last few years, the transmission distances have been increased dramatically due to the use of Er-doped fiber amplifiers. High power semiconductor lasers at either 0.98 tm or 1.48 .tm wavelengths are used for the pump. The powers into the amplifier required for both pump wavelengths are about 20 mW and 50 mW respectively. On the other hand, semiconductor opticai amplifiers are attractive for monolithic integration with lasers, waveguides, modulators, wavelength multiplexers and demultiplexers. For example multi-wavelength DFB laser arrays, as many as 20 wavelengths, have been integrated monolithically with wavelength combiners (star coupler) and optical amplifiers on InP substrate [2). These integrated multi-wavelengths DFB laser arrays have the advantage of easier wavelength control and lower cost per wavelength than the discrete DFB laser transmitters for WDM applications. Such photonic integrated circuits (PlC) can increase the functionality and reduce the optical fiber-to-device interfaces that are the main factor for the high cost of optoelect.ronic components. The fiber-to-device interface is also the major concern for component reliability.