Harvard College

Christian Pflugl

Federico Capasso

Laurent Diehl

C Kumar N Patel

Mikhail A Belkin

Arkadiy Lyakh

Richard Maulini

Alexei Tsekoun

Benjamin G Lee

Qijie Wang

Methods and apparatus for improved single-mode selection in a quantum cascade laser. In one example, a distributed feedback grating incorporates both index-coupling and loss-coupling components. The loss-coupling component facilitates selection of one mode from two possible emission modes by periodically incorporating a thin layer of 'lossy' semiconductor material on top of the active region to introduce a sufficiently large loss difference between the two modes. The lossy layer is doped to a level sufficient to induce considerable free-carrier absorption losses for one of the two modes while allowing sufficient gain for the other of the two modes. In alternative implementations, the highly-doped layer may be replaced by other low-dimensional structures such as quantum wells, quantum wires, and quantum dots with significant engineered intraband absorption to selectively increase the free-carrier absorption losses for one of multiple possible modes so as to facilitate single-mode operation.

Methods and apparatus for single-mode selection in quantum cascade lasers

A quantum cascade laser utilizing non-resonant extraction design having a multilayered semiconductor with a single type of carrier; at least two final levels (and) for a transition down from level; an energy spacing Egreater than E; an energy spacing Eof about 100 meV; and an energy spacing Eabout equal to E. The carrier wave function for leveloverlaps with the carrier wave function for level. Likewise, the carrier wave function for level' overlaps with the carrier wave function for level. In a second version, the basic design also has an energy spacing Eof about 90 meV, and levelsand&#x2032; do not have to be spatially close to each other, provided that levelhas significant overlap with both these levels. In a third version, there are at least three final levels (, and) for a transition down from level. Each of the levels, andhas a non-uniform squared wave function distribution.

Quantum cascade laser

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Cambridge, MA, United States of America

Christian Pflugl