Kuo‐Liang Chen

Cross‐talk problems in optical directional couplers

Cross‐talk in optical directional couplers is usually considered to be limited only by the processing technology. We show that unequal coupling of an input wave to the even and the odd mode of the coupling region gives rise to another kind of cross‐talk. The extinction ratio is well approximated by the overlap integral of the fields in the two waveguides. For a given coupling length, the higher the index step a waveguide has, the less the cross‐talk is. For straight couplers without bends one way to eliminate the cross‐talk is to offset the input wave relative to the coupled guides with the penalty of power loss. A three‐waveguide coupler has a different cross‐talk problem of comparable magnitude.

Spatial hole burning problems in evanescently coupled semiconductor laser arrays

The effect of spatial hole burning on laser arrays is theoretically analyzed. Due to the nonuniformity of the lowest order supermode, carriers are unevenly depleted when this mode is excited. This spatial hole burning in carrier concentration reduces any designed discrimination against higher order supermodes. More and more modes are excited as the power level goes up, resulting in broadened radiation patterns. Even when the lowest order mode oscillation can be guaranteed, spatial hole burning modifies the refractive index profile. The intensity distribution of this mode narrows as power increases. The results are broadened radiation patterns and low quantum efficiency. Two methods to overcome these problems are briefly discussed.

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.

Single-longitudinal-mode GaAs/GaAlAs channeled-substrate lasers grown by molecular beam epitaxy

We present here the first simple double‐heterostructure channeled‐substrate laser with lateral index guiding grown by molecular beam epitaxy. The channel is along [110] direction. The threshold current is 60 mA. Linear light‐current relation and stable far‐field patterns have been observed over the range of currents tested (from 60 to 160 mA). The lasers operate in single longitudinal mode over a wide range of current. The intensity ratio of the dominant mode and the neighboring mode is greater than 100:1.

Longitudinal mode behavior in a separately pumped, multiple twisted double-heterostructure laser

Behavior of longitudinal modes in a separately pumped, multiple twisted double-heterostructure laser is investigated. A single longitudinal mode operation is observed in the current range up to 1.3I/sub th/ under uniform pumping. The lasing wavelength is locked to a single longitudinal mode over a temperature range of 12 /sup 0/C under uniform pumping. A continuous tuning range of 3.3 A is obtained in one longitudinal mode. The wavelength shifts at a rate of 0.07 A/mA in the continuous tuning range.