Demonstration of post-growth wavelength setting of VCSELs using high-contrast gratings.

We demonstrate, for the first time, post-growth wavelength setting of electrically-injected vertical-cavity surface-emitting lasers (VCSELs) by using high-contrast gratings (HCGs) with different grating parameters. By fabricating HCGs with different duty cycle and period, the HCG reflection phase can be varied, in effect giving different optical cavity lengths for HCG-VCSELs with different grating parameters. This enables fabrication of monolithic multi-wavelength HCG-VCSEL arrays for wavelength-division multiplexing (WDM). The GaAs HCG is suspended in air by removing a sacrificial layer of InGaP. Electrically-injected 980-nm HCG-VCSELs with sub-mA threshold currents indicate high reflectivity from the GaAs HCGs. Lasing over a wavelength span of 15 nm was achieved, enabling a 4-channel WDM array with 5 nm channel spacing. A large wavelength setting span was enabled by an air-coupled cavity design and the use of only the HCG as top mirror.

Characterization of human scalp hairs by optical low-coherence reflectometry.

Optical low-coherence reflectometry is used to investigate the internal structure and optical properties of human scalp hair. Regardless of hair color, the refractive index of the cortical region remains within the range of 1.56-1.59. The amplitude of the backscattered infrared light coupled into different-colored hair confirms the relative melanin content. Discontinuities in the refractive index permit identification of distinct structural layers within the hair shaft.

Optical receiver design for high optical return loss.

A new fiber pigtailed optical receiver design using a single gradient-index rod lens with a beveled exit face achieved a broadband optical return loss of > 65 dB, which was limited by the diffuse reflection from the photodetector front surface. By contrast the optical return loss for a receiver with an unbeveled lens exit face and an on-axis optical path was limited to a smaller value by the specular reflection from the lens exit face.

High-performance single-mode fiber polarization-independent isolators.

The design and performance of polarization-independent isolators that are substantially insensitive to variations of temperature and wavelength are presented. Three single-mode fiber isolators have been designed, constructed, and tested. The first isolator is a 1.3-microm two-stage isolator that has more than 40 dB of isolation and less than 2.0 dB of insertion loss over the temperature range of 15-70 degrees C. The second isolator is a two-stage dual-wavelength isolator with an insertion loss of less than 4 dB and an isolation of better than 35 dB at 1.3 and 1.52 microm over the temperature range of 15-75 degrees C. The third isolator is a three-stage isolator with an insertion loss of less than 2.5 dB and an isolation of better than 63 dB over the wavelength range 1275-1355 nm.

Single-frequency output from a broadband-tunable external fiber-cavity laser.

Single-frequency operation is demonstrated by using a semiconductor laser coupled to a tunable fiber-optic reflective filter. This external fiber-cavity laser is stepwise tunable over a 66-nm range centered around 1300 nm. Short-term laser linewidths are measured to be less than 50 kHz.

Highly selective evanescent modal filter for two-mode optical fibers.

Efficient and selective coupling between a single-mode fiber and the LP(11) mode of a double-mode fiber is demonstrated in an evanescent directional coupler. With greater than 90% coupling to the LP(11) mode, suppression of the coupled power to the lower-order LP(01) mode was measured to be at least 24 dB. This device has application as a modal filter for the construction of in-line all-fiber optical components.

Single-mode-fiber ring dye laser.

Pulsed dye-laser operation in a single-mode fiber is demonstrated by incorporating an evanescent field amplifier into an all-fiber ring resonator. Laser threshold is obtained with 60 mW of pump power. Characteristics of the vanescent fiber amplifier are investigated as functions of pump power and dye solution index.

Single-mode-fiber saturable absorber.

Saturable absorption is performed on a signal in a single-mode fiber by allowing the evanescent field of the guided wave to interact with a saturable-absorbing dye. The evanescent field is exposed by mechanically removing a portion of the fiber cladding. The saturable material is then placed in close proximity to the fiber core. The singlemode-fiber saturable absorber is characterized by a nonlinear transmission versus input optical intensity. Transmissions ranging from 50 to 80% have been demonstrated using Eastman 9860 saturable-absorbing dye and optical pulses from a Q-switched Nd:YAG laser.