Y. Twu

Growth and characterization of high yield, reliable, high-power, high-speed, InP/InGaAsP capped mesa buried heterostructure distributed feedback (CMBH-DFB) lasers

The capped-mesa buried-heterostructure distributed-feedback (CMBH-DFB) laser structure requires three epitaxial growths and is designed to allow good control of the width of the active layer using straightforward chemical etching techniques. The base structure, which contains the active layer, was fabricated using a variety of epitaxial techniques: liquid-phase epitaxy, hydride vapor-phase epitaxy (VPE) and metalorganic vapor-phase epitaxy (MOVPE). The final cap growth was done using hydride VPE. High yields of low-threshold high-power DFB lasers were produced from a number of wafers at emission wavelengths of 1.3 and 1.55 mu m. >

High power coupled ridge waveguide semiconductor laser arrays

Using index‐guided ridge waveguide structures, we have obtained single‐lobe far‐field pattern from coupled multiple‐stripe semiconductor laser arrays. A stable far‐field pattern has been observed up to 250‐mW peak pulsed power. This desired performance of a semiconductor laser array is achieved by intentional pumping of a laser array at coupling regions, which is possible in ridge waveguide structures.

Semiconductor laser damage due to human-body-model electrostatic discharge

Various types of InP-based semiconductor lasers, Fabry–Perot (FP), and distributed feedback (DFB), in different wavelength regions of 1.3, 1.48, and 1.55 μm have been subjected to human-body-model electrostatic discharge (ESD) testing. The reverse V-I characteristics of these diode lasers were found to be generally most sensitive in detecting ESD damage than the forward characteristics (e.g., threshold current) of the laser. The laser ESD failure voltages were much lower for the reverse than the forward polarity and DFB lasers were found to be more vulnerable to ESD than FP lasers. The failure mechanism was found to be due to localized melting—a thermal effect—in both polarities of ESD testing. We also report the study of the latent ESD effects on the long-term aging rates of semiconductor lasers.

1.55-μm optical logic étalon with picojoule switching energy made of InGaAs/InP multiple quantum wells

We have constructed all‐optical logic etalons operating in the 1.55‐μm wavelength region using InGaAs/InP multiple quantum well (MQW) structures. These etalons have low‐energy requirements with several nanosecond recovery times, exhibit high on/off contrast (>20:1 if desired) with large on‐state transmission (>40%), and have signal gain, thus making them possible to cascade. For example, we have performed gating using 6 pJ input energy with 5:1 contrast and gain about 2 at 100 MHz operating frequency. These etalons also show optical bistability. The nonlinear coefficients for the InGaAs/InP MQW’s deduced from experimental results are found to be on the same order as those for GaAs/GaAlAs MQW’s.

Eigenmode analysis of phase-locked semiconductor laser arrays

A self‐consistent model of phased‐array diode lasers, which takes into account the interaction of the carrier and the field, is presented with numerical simulations on both ideal dielectric coupled waveguides and active phased arrays. While essential agreement between the results of this model and those of coupled mode analysis is obtained for passive waveguides, important differences are found for active arrays. Our results show the development of patterns for the various array modes in the active regions.

Fabrication and performance characteristics of buried-facet optical amplifiers

The fabrication, performance characteristics, and design rules of buried-facet optical amplifiers are described. Chip gain of 25 dB, gain ripple of <1 dB, and gain difference of ≤1 dB for TE- and TM-polarized light are observed. The gain ripple and polarization dependence of gain correlate well with the ripple and polarization dependence of the amplified spontaneous emission spectrum. The performance of buried-facet amplifiers is comparable to that of cleaved-facet amplifiers with very good antireflection (R<10−4) coatings. The buried-facet design reduces the requirement on antireflection coatings and makes the fabrication process more reproducible.

Dynamic and CW linewidth measurements of 1.55- mu m InGaAs-InGaAsP multiquantum well distributed feedback lasers

Measurement of the CW linewidth and frequency chirp as functions of modulation data rate and bias level for 1.55- mu m InGaAsP multiquantum-well distributed feedback lasers grown by low-pressure MOCVD are presented. The results show that the CW linewidth of asymmetric facet-coated multiquantum-well DFB lasers can be as low as 2.0 MHz at 13.5 mW output power. The frequency chirp increases with modulation data rate and is significantly larger if the laser off-state is below threshold than if it is above threshold. The 20 dB down chirp widths are in the range of 1.9-5 AA for 40 mA peak-to-peak modulation current at 10 Gb/s under above-threshold bias.<<ETX>>

Temperature dependence of polarization characteristics in buried facet semiconductor laser amplifiers

The temperature dependence of gain and amplified spontaneous power for both TE and TM modes in semiconductor laser amplifiers are measured. Experiments are performed on three selected amplifier types, with higher TE, higher TM, and equal TE-TM gains, respectively. The gain differences are significantly reduced at higher temperature for the TE-dominant and TM-dominant amplifiers. For amplifiers with equal TE-TM gains, the TE and TM gains remain equal at high temperature. The measurements of the amplified spontaneous power show similar similar characteristics. More importantly, less polarization-sensitive gain characteristics can be obtained with some decrease in maximum gain by raising the operating temperature. The experimental results are explained by using the gain equations of the semiconductor laser amplifier. >

Mode characteristics of phase-locked semiconductor laser arrays at and above threshold

A detailed eigenmode analysis of diode laser phased arrays both at and above threshold condition is presented. This analysis is based on the models developed for stripe-geometry diode lasers, in which the field equation is solved self-consistently with the carrier equation by taking into account the effect of carriers on the effective refractive index and including the stimulated emission in the carrier equation. The effect of a varying transverse confinement factor across the array is included. Numerical simulation results are obtained for threshold currents as well as laser behavior above the threshold, including the carrier density distribution, perturbed index distribution, array-mode patterns, and their associated far-field intensity distribution. Special attention has been paid to the development of the various array modes at power levels at which two array modes are oscillating simultaneously and the third one just reaches threshold.

Frequency modulation responses of two‐electrode distributed feedback lasers

Frequency modulation (FM) response of a 1.3 μm two‐electrode distributed feedback laser is studied in detail. We found that by adjusting the injection current applied to the modulated section, the FM bandwidth can be increased to a value as high as 900 MHz. However, as the bandwidth increases, the FM sensitivity decreases proportionally. This behavior is described satisfactorily by below‐threshold carrier rate equation and shown to be closely related to the injected carrier lifetime.