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We report, to the best of our knowledge, the first demonstration of a 1555-nm stepped-height ridge waveguide polarization mode converter monolithically integrated with a sidewall grating distributed-feedback (DFB) laser using the identical epitaxial layer scheme. The device shows stable single longitudinal mode (SLM) operation with the output light converted from TE to TM polarization with an efficiency of >94% over a wide range of DFB injection currents (IDFB) from 140 mA to 190 mA. The highest TM mode purity of 98.2% was obtained at IDFB = 180 mA. A particular advantage of this device is that only a single step of metalorganic vapor-phase epitaxy and two steps of III-V material dry etching are required for the whole integrated device fabrication, significantly reducing complexity and cost.

A four-laser array based on sampled Bragg grating distributed feedback (DFB) lasers in which each sampled period contains four phase-shift sections is proposed, fabricated, and experimentally demonstrated. The wavelength spacing between adjacent lasers is accurately controlled to 0.8 nm ± 0.026 nm and the lasers have single mode suppression ratios larger than 50 dB. Using an integrated semiconductor optical amplifier, the output power can reach 33 mW and the optical linewidth of the DFB lasers can be as narrow as 64 kHz. This laser array uses a ridge waveguide with sidewall gratings and needs only one metalorganic vapor-phase epitaxy (MOVPE) step and one III-V material etching process, simplifying the whole device fabrication process, and meeting the requirements of dense wavelength division multiplexing systems.

We report an all-solid large-mode-area (LMA) step-index fiber offering high absorption and low core numerical aperture (NA) by introducing a highly ytterbium-doped P:Al core and germanium-doped cladding. The fiber provides core absorption of ∼1200 dB/m at 976 nm with a low 0.07 core NA, due to the raised Ge cladding. Furthermore, matched profiles of P and Al across the core are successfully obtained with high concentration of Yb2O3 around 0.4 mol%. The fiber characteristics are routinely achievable by conventional modified chemical vapor deposition with a solution doping technique. A highly efficient laser with >100 W output power, 86% slope efficiency with respect to launched pump power, and a mean M2 of 1.34 has been demonstrated using the fabricated LMA step-index fiber. We also report 80% laser slope efficiency with 58 W output power (pump power limited) within only 0.5 m of the fiber when pumped by a wavelength-stabilized laser diode. Accepted version

A widely tunable dual-mode distributed feedback (DFB) laser fabricated by selective area growth (SAG) technology integrated with Ti heaters was demonstrated. In the device, an original mode spacing of 4 nm was obtained by the simple SAG technology. Ti thin-film heaters were integrated with a novel procedure, which simplifies the fabrication of such heaters greatly. A large electrical resistance of the heaters is obtained at the same time, resulting in a high wavelength tuning efficiency. An accurate mode spacing as small as 0.34 nm and as large as 8.06 nm is achieved, which corresponds to a wide beat frequency range from 42.2 GHz to 1 THz. The simple fabrication process indicates that it is promising for reducing the cost of dual-mode DFB laser in fabricating self-pulsation lasers and THz generators.

By altering the lattice geometry of the photonic crystal (PhC) surface-emitting lasers (PCSELs), we tune the regular lasing band edges of quadratic dispersions to form a single accidental Dirac point of linear dispersion at the Brillouin zone center. This not only increases the mode spacing by orders of magnitude but also eliminates the distributed in-plane feedback to enable single-mode PCSELs of substantially larger area and thus substantially higher output power. The advantages of using accidental Dirac cones are systematically evaluated through two-dimensional in-plane calculations and confirmed by three-dimensional simulations of PhC slab devices., National Science Foundation (U.S.) (MRSEC Program, award no. DMR-0819762), United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001), United States. Dept. of Energy (MIT S3TEC Energy Research Frontier Center, Grant No. DE-SC0001299), Spain. Ministerio de Ciencia e Innovación (Ramon-y-Cajal program, Grant No. RyC-2009-05489)

A novel design of a two-mode de/multiplexer (DE/MUX) based on multimode interference (MMI) couplers is presented. Instead of the phase shifter (PS) in the shape of a narrow strip waveguide, which needs tight design and fabrication requirements, a tilted joint is used as a PS in the proposed device, so that the effects of the fabrication errors of the PS on the performance of the device can be reduced greatly. Simulations show that while the size of the device is as small as 39.54 μm, which is more compact than other MMI-based DE/MUX, the fabrication tolerance is larger than ±25 nm. Within the entire C-band wavelength range, the de-multiplexing crosstalk of the device is lower than -28 dB and the insertion loss is below 1.0 dB.

A mode-hop-free single-mode laser with a two-dimensional photonic crystal was demonstrated. In the device, the photonic crystal was realized by double holographic exposure technology. This novel procedure simplifies the fabrication of such structures greatly. The design of a reverse junction in the photonic crystal layer induces a partial gain coupling into the laser, which could break the symmetry of the transmission spectrum and realize stable single-mode lasing of the laser. The fabricated device has a high single-mode stability and side-mode suppression ratio of over 45 dB without mode hop at a relatively wide injected current range. The measurement results indicate that the laser with a simple fabrication process is promising as a stable single-mode and high-power light source in optical communication systems.

A practical technique based on the phase-conjugate wave (PCW) generation is proposed to improve the temporal contrast of the picosecond pulses. Our theory predicts the temporal contrast of the picosecond pulses can be enhanced to about the cube of the temporal contrast of the input pulse via the PCW generation, in which the conversion efficiency from the incident pulse to the PCW is about 25%. In a proof-of-principle experiment, the temporal contrast of picosecond pulses was enhanced from 1.7×10(3) to 8.6×10(8) with the conversion efficiency of 10%. This technique is promising to effectively eliminate the background of the ultrashort and ultraintense laser pulses in the future.

We report an InP-based deep-ridge NPN transistor laser (TL, λ∼1.5 μm). By placing the quantum well (QW) active material above the heavily Zn-doped base layer, both the optical absorption of the heavily p-doped base material and the damage of the quality of the QWs resulted from the Zn diffusion into the QWs are decreased greatly. CW operation of the TL is achieved at -40 °C, which is much better than the shallow-ridge InP-based NPN TL. With future optimization of the growth procedure, significant improvement of the performance of the deep-ridge InP-based NPN TLs is expected.