H.M. Shen

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.

220-fs erbium-ytterbium:glass laser mode locked by a broadband low-loss silicon/germanium saturable absorber.

We demonstrate femtosecond performance of an ultrabroadband high-index-contrast saturable Bragg reflector consisting of a silicon/silicon dioxide/germanium structure that is fully compatible with CMOS processing. This device offers a reflectivity bandwidth of over 700 nm and subpicosecond recovery time of the saturable loss. It is used to achieve mode locking of an Er-Yb:glass laser centered at 1540 nm, generating 220-fs pulses, with what is to our knowledge the broadest output spectrum to date.

Oxidized GaAs/AlAs mirror with a quantum-well saturable absorber for ultrashort-pulse Cr4+:YAG laser

Abstract Ultra-broadband saturable Bragg reflectors consisting of a 7-period GaAs/Al x O y Bragg mirror and an InGaAs/InP quantum well were studied and used to start modelocking of 36 fs pulses near 1500 nm in a dispersion compensated Cr 4+ :YAG laser. The mirrors are comprised of high-index-contrast GaAs/Al x O y Bragg stacks grown as GaAs/AlAs and oxidized to create mirror areas as wide as 300 μm. They exhibit non-saturable losses smaller than 0.8% and a stopband from 1300 to 1800 nm, indicating the potential for the generation of shorter pulses.

Large-area broadband saturable Bragg reflectors by use of oxidized AlAs

Broadband saturable Bragg reflectors (SBRs) are designed and fabricated by monolithic integration of semiconductor saturable absorbers with broadband Bragg mirrors. The wet oxidation of AlAs creates low-index AlxOy layers for broadband, high-index-contrast AlGaAs/AlxOy or InGaAlP/AlxOy mirrors. SBR mirror designs indicate greater than 99% reflectivity over bandwidths of 294, 466, and 563 nm for center wavelengths of 800, 1300, and 1550 nm, respectively. Highly strained and unstrained absorbers are stably integrated with the oxidized mirrors. Large-scale lateral oxidation techniques permit the fabrication of SBRs with diameters of 500 microm. Large-area, broadband SBRs are used to self-start and mode lock a variety of laser systems at wavelengths from 800 to 1550 nm.

Silicon-germanium saturable absorber mirrors

A silicon-germanium ultra-broadband saturable Bragg reflector with sub-picosecond recovery time is fabricated. Its performance is demonstrated by mode-locking an Er-Yb glass laser generating 220 fs pulses spanning the C-band of the optical communication range.

Large scale oxidation of AlAs layers for broadband saturable Bragg reflectors

Summary form only given. Describes oxidation of AlAs to Al/sub x/O/sub y/ for use as a broadband saturable Bragg reflector (SBR) where an Al/sub x/O/sub y//GaAs mirror with lateral dimensions >300 /spl mu/m is required. For the SBR structure described, the simulated bandwidth extends from 1200 nm to 1800 nm with greater than 99.5% reflectivity. The layers within the SBR are grown using gas-source molecular beam epitaxy. The SBR structure contains an 8 period GaAs/AlAs quarter-wave stack grown on a GaAs substrate. The Al/sub x/O/sub y/ layer is initially grown as AlAs and later oxidized. The AlAs layer is relatively thick (240 nm) to correspond to a quarter wavelength in Al/sub x/O/sub y/ (n = 1.66) minus a 10% shrinkage upon oxidation. The active region consists of an InP/InGaAs quantum well emitting near /spl lambda/ = 1550 nm. The effects of the SBR for self-starting the laser cavity are detailed.

A few-cycle Cr/sup 4+/:YAG laser

Summary form only given. Kerr-lens mode locked Cr/sup 4+/:YAG lasers are used to generate ultrashort optical pulses near 1.5 /spl mu/m because of their large spectral bandwidth. Pulses as short as 43 fs and 44 fs self-started by a saturable absorber mirror have been generated from Cr/sup 4+/:YAG lasers using fused silica prism pairs for group velocity dispersion compensation.

Si/Ge Semiconductor Saturable Bragg Reflectors for Integrated Mode-Locked Lasers

Silicon-germanium saturable absorber mirrors at 1550 nm are demonstrated. The device is used to achieve stable, continuously mode-locked operation of an Er-Yb:glass laser centered at 1540 nm, generating 220 fs pulses

Silicon-Germanium Saturable Absorber Mirrors for Ultra-Short Pulse Generation

Materials Processing Center and, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Silicon-Germanium saturable absorber mirrors are developed for laser mode locking. The fabrication process is fashioned such that a highly reflecting Si/SiO2 Bragg mirror with a crystalline absorber top-layer is generated. One step of wafer-bonding allows for subsequent epitaxial growth on the mirror. A six-pair reflector centered at 1400 nm with 99.8% peak reflectivity, a 99%-reflectivity bandwidth of 700 nm and a surface roughness of 0.136 nm is demonstrated. A thin Germanium layer is epitaxially deposited on the mirror surface to provide saturable absorption at 1550nm. with a sub-picosecond recovery time. The device is used to achieve stable, continuously modelocked operation of an Er-Yb:glass laser centered at 1540 nm, generating 220 fs pulses.

Novel highly nonlinear bismuth oxide fiber for supercontinuum generation

Supercontinuum generation is observed in highly nonlinear bismuth-oxide fiber with normal dispersion. The small effective area and high nonlinearity allow generation of smooth, spectrally-unstructured spectra from 1300 nm to > 1700 nm with sub-0.5 nJ pulse energies at 1540 nm.