There is strong interest in the development of tunable lasers and optical filters for a number of optoelectronic applications. From a telecommunications standpoint, compact, efficient, and affordable tunable sources and filters could find immediate widespread use for wavelength division multiplexing (WDM) systems, enabling incredibly dense optoelectronic communications over a single optical fiber. From a military standpoint, robust tunable sources would readily be inserted into platforms requiring fixed-wavelength optical pumps (such as for fiber amplifiers or atomic clock systems) or for hyperspectral imaging systems that require stable, pixilated filter elements.

We report our progress on the design and fabrication of electrostatically-actuated microelectromechanical (MEM) tunable wavelength filters and vertical cavity surface-emitting lasers (VCSELs). We investigate both an all-semiconductor monolithic approach and a hybrid approach based on the combination of conventional polysilicon microelectromechanical systems (MEMS) and III-V semiconductor thin-film distributed Bragg reflector (DBR) and VCSEL structures. In the tunable hybrid structures the III-V semiconductor layers are flip-bonded onto specially designed polysilicon foundry MEMS structures and separated from their lattice-matched parent substrates by a novel post-bonding lift-off process.

We report and use our micro-electro-mechanically tunable vertical cavity surface emitting laser (MEM-TVCSEL) computer-aided design methodology to investigate the resonant frequency design space for monolithic and hybrid MEM-TVCSELs. For various initial optical air gap thickness, we examine the sensitivity of monolithic or hybrid MEM-TVCSEL resonant frequency by simulating zero, two, and four percent variations in III-V material growth thickness. As expected, as initial optical airgap increases, tuning range decreases due to less coupling between the active region and the tuning mirror. However, each design has different resonant frequency sensitivity to variations in III-V growth parameters. In particular, since the monolithic design is comprised of III-V material, the shift in all growth thicknesses significantly shifts the resonant frequency response. However, for hybrid MEM-TVCSELs, less shift results, since the lower reflector is an Au mirror with reflectivity independent of III-V growth variations. Finally, since the hybrid design is comprised of a MUMPS polysilicon mechanical actuator, pull-in voltage remains independent of the initial optical airgap, between the tuning reflector and the III-V material. Conversely, as the initial airgap increases in the monolithic design, the pull-in voltage significantly increases.

We characterize our novel mechanical structures for flipbonded hybrid micro-electro-mechanically (MEM) tunable filters (MEM-TF) and MEM-tunable vertical cavity surface emitting lasers (MEM-TVCSELs) by comparing simulations with foundry fabricated actuators. Two of our prototypes, each with different flexure thickness, have analytically simulated and measured pull-in voltages of (11.6 V, 11.8 ± 0.1 V) and (8.4 V, 7.7 ± 0.5 V) respectively. We believe our hybrid approach will reduce cost, shorten development time, enable use of standard flip-chip technology and IC/MEMS foundries, and offer materials flexibility since the components do not need to be lattice matched.

We report a tunable red vertical cavity surface emitting laser (VCSEL) with a flexible micro-electro-mechanical (MEM) top distributed Bragg reflector. The peak emission wavelength is electrically tunable over a range of 15 nm from 644 to 659 nm.

A tunable prototype red light-emitting n-p-n VCSEL with an n-doped micro-electromechanical (MEM) top distributed Bragg reflector is reported. The peak emission wavelength is tunable over a range of about 15 nm from 644 to 659 nm