Leslie A. Kolodziejski

Enhanced coupling to vertical radiation using a two-dimensional photonic crystal in a semiconductor light-emitting diode

Enhanced coupling to vertical radiation is obtained from a light-emitting diode using a two-dimensional photonic crystal that lies entirely inside the upper cladding layer of an asymmetric quantum well structure. A sixfold enhancement in light extraction in the vertical direction is obtained without the photonic crystal penetrating the active material. The photonic crystal is also used to couple pump light at normal incidence into the structure, providing strong optical excitation.

Two-photon absorption in semiconductor saturable absorber mirrors

The nonlinear reflectivity of semiconductor saturable absorber mirrors has been investigated as a function of incident energy fluence. The presence of two-photon absorption in commonly used structures was confirmed via time-resolved differential reflectivity measurements. Theoretical calculations predict that two-photon absorption will expand the continuous-wave mode-locking stability regime against Q-switched mode-locking, yet may simultaneously induce multiple pulses in a laser cavity.

Air‐bridge microcavities

We introduce and analyze a new type of high‐Q microcavity consisting of a channel waveguide and a one‐dimensional photonic crystal. A band gap for the guided modes is opened and a sharp resonant state is created by adding a single defect in the periodic system. An analysis of the eigenstates shows that strong field confinement of the defect state can be achieved with a modal volume less than half of a cubic half‐wavelength. We also present a feasibility study for the fabrication of suspended structures with micron‐sized features using semiconductor materials.

Compact, stable 1 GHz femtosecond Er-doped fiber lasers

We demonstrate a high-repetition-rate soliton fiber laser that is based on highly doped anomalously dispersive erbium-doped fiber. By splicing an 11 mm single-mode fiber to the erbium-doped fiber, the thermal damage of the butt-coupled saturable Bragg reflector (SBR) is overcome. The laser generates 187 fs pulses at a repetition rate of 967 MHz with a measured long-term stability of more than 60 h.

One-dimensional photonic bandgap microcavities for strong optical confinement in GaAs and GaAs/Al/sub x/O/sub y/ semiconductor waveguides

Photonic bandgap (PBG) waveguide microcavities with tightly confined resonant optical modes have been designed, fabricated using high-dielectric-contrast GaAs/Al/sub x/O/sub y/ III-V compound semiconductor structures, and characterized optically. The photonic crystal lattices are defined by one-dimensional (1-D) arrays of holes in waveguides, and a controlled defect in the spacing between two holes of an array defines a microcavity. Waveguide microcavity resonances have been studied in both monorail and suspended air-bridge geometries. Resonance states with cavity Qs as high as 360 were measured at wavelengths near 1.55 /spl mu/m, with modal volumes as small as 0.026 /spl mu/m, which corresponds to only two times (/spl lambda//2n)/sup 3/.

Guiding 1.5 μm light in photonic crystals based on dielectric rods

Photonic-crystal structures consisting of dielectric rods were designed, fabricated, and optically characterized. The combination of the high refractive-index-contrast GaAs∕AlxOy material system with electron-beam lithography enabled the fabrication of structures suitable for the optical propagation of 1.5 μm light. Experimental transmission spectra were obtained for structures consisting of a two-dimensional array of rods and line-defect waveguides. Optical measurements confirmed the presence of a photonic band gap, as well as band gap guidance in the line-defect waveguide. A two-stage coupling scheme facilitated efficient optical coupling into the line-defect waveguide.

Erbium-ytterbium waveguide laser mode-locked with a semiconductor saturable absorber mirror

Picosecond pulses are produced using a semiconductor saturable absorber mirror in a laser based on an Er-Yb codoped planar waveguide amplifier. Continuous-wave mode-locking (CWML) with 9.8-ps pulses is obtained at repetition rates up to 100 MHz. With intracavity spectral filtering, saturable pulsewidths of 1 ps are achieved, and tunable picosecond pulses are obtained from 1534 to 1553 nm. Absorber characterization suggests that two-photon absorption within the saturable absorber mirror influences the CWML stability.

Low-cost, single-mode diode-pumped Cr:Colquiriite lasers

We present three Cr3+:Colquiriite lasers as low-cost alternatives to Ti:Sapphire laser technology. Single-mode laser diodes, which cost only

Reduction of structural defects in II–VI blue green laser diodes

150 each, were used as pump sources. In cw operation, with approximately 520 mW of absorbed pump power, up to 257, 269 and 266 mW of output power and slope efficiencies of 53%, 62% and 54% were demonstrated for Cr:LiSAF, Cr:LiSGaF and Cr:LiCAF, respectively. Record cw tuning ranges from 782 to 1042 nm for Cr:LiSAF, 777 to 977 nm for Cr:LiSGaF, and 754 to 871 nm for Cr:LiCAF were demonstrated. In cw mode-locking experiments using semiconductor saturable absorber mirrors at 800 and 850 nm, Cr:Colquiriite lasers produced approximately 50-100 fs pulses with approximately 1-2.5 nJ pulse energies at approximately 100 MHz repetition rate. Electrical-to-optical conversion efficiencies of 8% in mode-locked operation and 12% in cw operation were achieved.

MBE growth of films and superlattices of diluted magnetic semiconductors

Early blue/green laser diodes based on ZnSe exhibited room temperature, continuous wave (cw) lifetimes of the order of a minute. Similar to the history of (Al,Ga)As lasers, the source of the degradation was the presence of extended crystalline defects. The dominant extended defects in the early room temperature cw lasers originated as stacking faults generated at the ZnSe/GaAs heterovalent nucleation event, and exhibited densities of the order of 106 cm−2. In this letter, a procedure is described which will ensure a consistent run to run reduction of the density of such extended defects to the mid to low 103 cm−2 over a 3 in. wafer.