By doping an organic compound functioning as an electron donor (hereinafter referred to as donor molecules) into an organic compound layer contacting a cathode, donor levels can be formed between respective LUMO (lowest unoccupied molecular orbital) levels between the cathode and the organic compound layer, and therefore electrons can be injected from the cathode, and transmission of the injected electrons can be performed with good efficiency. Further, there are no problems such as excessive energy loss, deterioration of the organic compound layer itself, and the like accompanying electron movement, and therefore an increase in the electron injecting characteristics and a decrease in the driver voltage can both be achieved without depending on the work function of the cathode material.

Light Emitting Device

Room temperature lasing from optically pumped single defect in a two-dimensional photonic bandgap crystal is illustrated. The high Q optical microcavities are formed by etching an array of air holes into a half wavelength thick multiquantum well waveguide. Defects in the two-dimensional photonic crystal or used to support highly localized optical modes with volumes ranging from 2 to 3 (λ/2n)3. Lithographic tuning of the air hole radius and the lattice spacing is used to match the cavity wavelength to the quantum well gain peak, as well as to increase cavity Q. The defect lasers were pumped with 10-30 nsec pulse of 0.4-1 percent duty cycle. The threshold pump power was 1500 milliwatts. The confinement of the defect mode energy to a tiny volume and the enhancement of the spontaneous emission rate make the defect cavity an interesting device for low threshold, high spontaneous emission coupling factor lasers, and high modulation rate light emitting diodes. Optic structures formed from photonic crystals also hold promise due to the flexibility of their geometries. Lithographic methods may be employed to alter the photonic crystal geometry so as to tune device characteristics. The integration of densely packed photonic crystal waveguides, prisons, and light sources integrated on a single monolithic chip is made possible. Lithographically defined photonic crystal cavities may also find use in some material systems as an alternative to epitaxially grown mirrors, such as for long wavelengths vertical cavity surface emitting lasers (VCSEL) and GaN based devices.

Tuneable photonic crystal lasers and a method of fabricating the same

A new time-domain Fourier-Galerkin (TDFG) theory is developed to simulate the near-field, far-field and spectral characteristics of surface-emitting photonic-crystal distributed-feedback (SE PCDFB) lasers. It is found that a properly-designed two-dimensional hexagonal or square-lattice grating should efficiently couple the output into a single SE mode that retains coherence for aperture diameters of up to /spl ap/1 mm. We identify lattice structures and precise conditions under which all components of the transverse electric or transverse magnetic polarized optical fields constructively interfere to produce a single-lobed, near-diffraction-limited circular output beam. The TDFG simulations predict that quantum efficiencies as high as 30% (60% if reflectors are built into the waveguide structure) should be attainable. A surprising conclusion is that diffractive coupling into the surface-emitting direction must be relatively weak, in order to assure selection of the desired symmetric in-phase mode. Furthermore, gain media with a moderate linewidth enhancement factor should produce the best SE PCDFB performance, whereas edge emitters nearly always benefit from a very small value.

Design optimization for high-brightness surface-emitting photonic-crystal distributed-feedback lasers

Two-dimensional photonic crystal surface-emitting laser comprising a two-dimensional photonic crystal, having media different in refractive index arrayed in a two-dimensional cycle, disposed in the vicinity of an active layer that emits light by the injection of carriers, wherein the two-dimensional photonic crystal consists of square lattices having equal lattice constants in perpendicular directions, and a basic lattice consisting of a square with one medium as a vertex has an asymmetric refractive index distribution with respect to either one of the two diagonals of the basic lattice to thereby emit light in a constant polarizing direction.

Two-dimensional photonic crystal surface-emitting laser

Because of an intrinsically low linewidth-enhancement factor, the quantum cascade laser (QCL) is especially favorable for patterning with a recently proposed 2-D photonic crystal (PC) lattice that substantially increases the device area over which optical coherence can be maintained. In this work, we use an original time-domain Fourier-transform (TDFT) algorithm to theoretically investigate the beam quality and spectral purity of gain-guided PC distributed-feedback (DFB) quantum cascade lasers. The conventional 1-D DFB laser and also the angled-grating DFB (/spl alpha/-DFB) laser are special cases of the PCDFB geometry. By searching the parameter space consisting of tilt angle, coupling coefficients, stripe width, and cavity length, we have theoretically optimized the PCDFB gratings for QCL gain regions. At a wavelength of 4.6 /spl mu/m, the simulations project single-mode emission from stripes as wide as 1.2 mm, and etendues of no more than three times the diffraction limit for 2-mm stripes. We also examine the tolerances required for single-mode and high-brightness operation. Comparisons are made to analogous simulations of a-DFB QCL lasers.

Photonic-crystal distributed-feedback quantum cascade lasers

A waveguide ( 10 ) is provided having a two-dimensional optical wavelength Bragg grating ( 20 ) embedded within a semiconductor laser medium ( 16 ). More particularly, the waveguide ( 10 ) includes an active region ( 16 ) sandwiched between n-doped and p-doped cladding layers ( 14, 22 ). The two-dimensional Bragg grating ( 20 ) is formed in the active region ( 16 ). Upper and lower electrodes ( 24, 26 ) are defined on opposite sides of the cladding layers ( 14, 22 ) to complete the waveguide structure ( 10 ). The two-dimensional grating ( 20 ) provides simultaneous frequency selective feedback for mode control in both the longitudinal and lateral directions.

High power single mode semiconductor lasers and optical amplifiers using 2D Bragg gratings

An optical device ( 10 ) including a first semiconductor layer ( 12 ) on which is deposited a dielectric layer that is patterned and etched to form dielectric strips ( 14 ) as part of a diffraction grating layer. Another semiconductor layer ( 16 ) is grown on the first semiconductor layer ( 12 ) between the dielectric strips ( 14 ) to provide alternating dielectric sections ( 14 ) and semiconductor sections. In an alternate embodiment, a dielectric layer is deposited on a first semiconductor layer ( 64 ), and is patterned and etched to define dielectric strips ( 66 ). The semiconductor layer ( 64 ) etched to form openings ( 68 ) between the dielectric strips ( 66 ). A semiconductor material ( 70 ) is grown within the openings ( 68 ) and then another semiconductor layer ( 72 ) is grown over the entire surface after removing the dielectric strips. Either embodiment may be modified to provide a diffraction grating with air channels ( 20 ).

Semiconductor-air gap grating fabrication using a sacrificial layer process

We demonstrate single mode operation of laser diode cavities up to 200|iim wide using 2-D Bragg gratings for simultaneous longitudinal and lateral mode control.

Large spatial mode, single frequency semiconductor lasers using two dimensionalgratings

PROBLEM TO BE SOLVED: To obtain a semiconductor laser which is capable of outputting a laser beam kept at a single mode and possessed of a facet region which is enhanced in volume. SOLUTION: A waveguide 10 is equipped with a two-dimensional optical wavelength Bragg grating 20 embedded inside a semiconductor laser medium 16. The waveguide 10 comprises an active region 16 sandwiched inbetween an N-type doped cladding layer 14 and a P-type doped cladding layer 22. The two-dimensional Bragg grating 20 is formed inside the active region 16. An upper electrode 24 and a lower electrode 26 are formed on both the sides of the cladding layers 14 and 22 for the formation of the waveguide 10. By the two-dimensional grating 20, a light of certain wavelength can be selectively fed back at the same time for controlling the mode of a semiconductor laser in both the longitudinal and a lateral direction.

High power single mode-semiconductor laser with two- dimensional bragg grating and optical amplifier

An optical device (10) including a first semiconductor layer (12) on which is deposited a dielectric layer that is patterned and etched to form dielectric strips (14) as part of a diffraction grating layer. Another semiconductor layer (16) is grown on the first semiconductor layer (12) between the dielectric strips (14), resulting in alternating dielectric sections (14) and semiconductor sections. In an alternate embodiment, a dielectric layer is deposited on a first semiconductor layer (64), and is patterned and etched to define dielectric strips (66). The semiconductor layer (64) is etched to form openings (68) between the dielectric strips (66). Another semiconductor material (70) is grown within the openings (68) and then another semiconductor layer (72) is grown over the entire surface after removing the dielectric strips (66). Either embodiment may be modified to provide diffraction grating with air channels (20).

Michael P. Nesnidal

Papers

High power single mode semiconductor lasers and optical amplifiers using 2D Bragg gratings

Semiconductor-air gap grating fabrication using a sacrificial layer process

Large spatial mode, single frequency semiconductor lasers using two dimensionalgratings

High power single mode-semiconductor laser with two- dimensional bragg grating and optical amplifier

High index-step grating fabrication using a regrowth-over-dielectric process