Tunable, Single-Frequency, Fiber Fabry-Perot VCSELs

Goddard Space Flight Center, Greenbelt, Maryland

The figure depicts several aspects of a unique type of vertical-cavity surface-emitting lasers (VCSELs) that incorporate fiber Fabry-Perot (FFP) optical cavities. These lasers have been designed to be compact, compatible with optical fibers, capable of single-frequency operation, and tunable. Lasers of this type that operate in frequency bands centered at wavelengths of about 850 and about 1,300 nm have been demonstrated.

In a laser of this type, a partial VCSEL and an FFP are incorporated with other optical components in a hybrid structure. The partial VCSEL is of a half-cavity design that features (1) a semiconductor distributed Bragg reflector (DBR) as the mirror on the surface opposite the emitting surface and (2) a multiple-quantum-well (MQW) gain region with an uncoated emitting surface. An airgap separates the emitting surface of the MQW from the end facet of a single-mode optical fiber that is held in a glass ferrule. The output mirror is a dielectric one that can be either deposited on the end facet of the fiber or else embedded within an optical-waveguide assembly that comprises two collinear single-mode-optical-fiber/glass-ferrule subassemblies. The combination of the half-cavity VCSEL and the output mirror on or in the fiber constitutes a fiber Fabry-Perot surface-emitting laser (FFP-SEL). Wavelength tuning is achieved by using a piezoelectric transducer to change the length of the airgap.

A Surface-Emitting Laser in a Fiber Fabry-Perot Cavity can operate in a single mode and can be tuned in wavelength by adjusting the airgap.

An 850-nm laser of this type is electrically pumped. A 1,300-nm laser of this type is optically pumped at a wavelength of 980 nm; in this case, the single-mode optical fiber is connected to a 980-nm/1,300-nm wavelength-division multiplexer (WDM) to enable both continuous pumping at 980 nm and output coupling at 1,300 nm.

Both the 850- and the 1,300-nm lasers have been shown to be capable of single-longitudinal-mode, single-transverse-mode, and single-polarization-state operation. Tests have shown that the 850-nm lasers are continuously tunable over a wavelength range ≈10 nm wide, and that their output power levels range up to about 1 mW. The 1,300-nm lasers in which the output mirrors are on the ends of the single-mode optical fibers have been shown to be capable of continuous tuning over a wavelength range≈40 nm wide, with output power levels up to tens of microwatts. The 1,300-nm lasers in which the mirrors are incorporated into the single-mode-optical-fiber waveguides have been shown to be capable of tuning over a wavelength range slightly less than 10 nm wide, with output power levels up to about 400 µW; the optical-waveguide mirrors clearly exhibit the advantage of mode-field confinement. By use of a FFP scanning interferometer with a resolution of about 42 MHz, the spectral line width of a 1,300-nm laser with an optical-waveguide mirror was determined to be <260 MHz.

This work was done by Kevin Hsu and Calvin M. Miller of Micron Optics, Inc., for Goddard Space Flight Center.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Goddard Space Flight Center; (301) 286-7351. Refer to GSC-14249.