Noriyuki Yokouchi

Two-dimensional photonic crystal confined vertical-cavity surface-emitting lasers

The two-dimensional photonic crystal (2-D PhC) structure has been investigated as a method for lateral mode control of vertical-cavity surface-emitting lasers (VCSELs). The 2-D PhC structures were designed using an equivalent index model developed for photonic crystal fibers combined with a plane wave expansion method. The etching depth dependence of the PhC structure was incorporated for the first time to design practical devices. 2-D PhC-confined VCSELs are demonstrated to operate in single PhC-confined mode using either a single- or seven-point defect.

Etching depth dependence of the effective refractive index in two-dimensional photonic-crystal-patterned vertical-cavity surface-emitting laser structures

A vertical-cavity surface-emitting laser (VCSEL) having a two-dimensional (2-D) photonic crystal structure on its surface has been investigated for single-lateral-mode operation. We evaluated the effective index change of a VCSEL cavity introduced by a 2-D pattern. Our experimental results showed good agreement with a theoretical model in which the influence of a finite etching depth was taken into consideration. The etching-depth dependence parameter γ, which can be explained by the optical power distribution inside a VCSEL structure, will be helpful for controlling the lateral mode of VCSEL devices.

Transverse modes of photonic crystal vertical-cavity lasers

The control of lateral mode operation using a photonic crystal in a vertical-cavity surface-emitting laser (VCSEL) is analyzed and confirmed experimentally. By controlling design parameters of the photonic crystal pattern, we have produced photonic crystal VCSELs that operate in higher order defect modes in addition to the fundamental defect mode. The transverse modal behavior is consistent with the predictions of a theoretical model in which the etching depth dependence of the air holes of the photonic crystals is considered. We also have determined the lower limit of optical confinement required from the photonic crystal pattern to influence the output beam of the laser.

Vertical-cavity surface-emitting laser operating with photonic crystal seven-point defect structure

A vertical-cavity surface-emitting laser with a two-dimensional photonic crystal (PC) structure has been investigated for single lateral mode operation. The PC confined mode can be controlled by the lattice constant, the hole diameter, the etching depth, and the defect structure. A seven-point defect structure is proposed to enhance the confinement effect, which is diluted by finite hole depth of the PC structure. We obtained a pure PC confined mode under room-temperature cw conditions with a PC lattice constant of 2 μm, hole diameters of 1.0 and 1.4 μm, and depths of 1.85 and 1.92 μm, respectively.

Various low group velocity effects in photonic crystal line defect waveguides and their demonstration by laser oscillation

We investigated propagating modes in a two-dimensional photonic crystal slab waveguide with a line defect narrower than a single line missing hole structure from the low group velocity point of view. These modes showed low group velocities not due to the conventional distributed feedback (DFB) between a forward and a backward mode with the same lateral field distribution, but due to a DFB between modes with different lateral field distribution or property of a start point of a photonic-band-gap-guided mode. These low group velocities of over 40 were demonstrated as a Fabry-Perot lasing oscillation due to gain enhancement.

InAs Quantum Dot Lasers with Extremely Low Threshold Current Density (7 A/cm2/Layer)

This paper describes the successful stacking of multilayered InAs quantum dots (QD) on a GaAs substrate up to 12 layers. The laser oscillated from the ground state under the condition of mirror loss at less than 7–8 cm-1. The extremely low threshold current density per QD-layer of 7 A/cm2/layer was obtained with a lasing wavelength of 1.21 µm at room temperature, which is the lowest value for any known semiconductor laser.

Tensile-strained GaInAsP-InP quantum-well lasers emitting at 1.3 /spl mu/m

Tensile-strained GaInAsP-InP quantum-well (QW) lasers emitting at 1.3 /spl mu/m are investigated. Low-pressure metalorganic chemical vapor deposition (LP-MOCVD) is used for crystal growth. High-resolution X-ray diffraction shows good agreement with theoretical simulation, photoluminescence spectra have good energy separation between light-hole and heavy-hole bands due to biaxial tension. The lowest threshold current density for infinite cavity length J/sub th//N/sub w//sup /spl infin// of 100 A/cm/sup 2/ is obtained for the device with -1.15% strain and N/sub w/=3. The amount of strain which gives the lowest J/sub th//N/sub w//sup /spl infin// experimentally clarified is around -1.2%. Threshold current of a buried-heterostructure (BH) laser is reduced to be as low as 1.0 mA. Enhanced differential gain of 7.1/spl times/10/sup -16/ cm/sup 2/ is also confirmed by measurements of relative intensity noise. Much improved threshold characteristic with the feasibility of submilliamp threshold current can be achievable by optimizing the BH structure. The tensile-strained QW laser emitting at 1.3 /spl mu/m with very low power consumption is attractive for the light source of fiber in the loop system and optical interconnection applications.

InAsP/InGaP All-Ternary Strain-Compensated Multiple Quantum Wells and Their Application to Long-Wavelength Lasers

By introducing InGaP tensile-strained layers as barriers of InAsP compressively strained multiple quantum wells, InAsP/InGaP strain-compensated multiple quantum wells with high crystalline quality were successfully grown by metalorganic chemical vapor deposition. For the first time, a laser, emitting at 1.2 µ m, consisting of all-ternary quantum wells as an active layer was fabricated. The threshold current density of 1 kA/cm2 was obtained without the use of a separate confinement heterostructure layer for a cavity length of 1000 µ m.

Very high characteristic temperature and constant differential quantum efficiency 1.3-/spl mu/m GaInAsP-InP strained-layer quantum-well lasers by use of temperature dependent reflectivity (TDR) mirror

A very high characteristic temperature T/sub 0/ of 150 K (25-70/spl deg/C) or 450 K (25-50/spl deg/C) and an almost constant differential quantum efficiency operation in the temperature range of 25-70/spl deg/C were achieved in 1.3-/spl mu/m GaInAsP-InP strained-layer quantum-well (SL-QW) lasers by use of a novel temperature dependent reflectivity (TDR) mirror composed of multiple quarter-lambda thickness /spl alpha/-Si-SiOx dielectric films with quarter-lambda shift in the vicinity of center portion, The mechanism of high T/sub 0/ and constant differential quantum efficiency were explained using the structural parameters, transparent current density and gain coefficient of a SL-QW laser that are derived experimentally. The effect of TDR mirror was confirmed by measuring the temperature dependence of net gain of a SL-QW laser with TDR mirror. It was found that less temperature dependent net gain due to the decrease of mirror loss with temperature played an important role for improving the temperature characteristics of threshold current. Almost constant differential quantum efficiency over a wide temperature range is attributed to the increase of the facet reflectivity with temperature. >

GaInAsP/InP Multi-Quantum Barrier (MQB) Grown by Chemical Beam Epitaxy (CBE)

A multi-quantum barrier (MQB) using the GaInAsP/InP system has been demonstrated for the first time. n-i-n tunneling diodes consisting of MQB and bulk barriers were grown by chemical beam epitaxy (CBE). From the measurement of 77 K current-voltage characteristics, the effective potential barrier height of 1.3 times the classical conduction band offset was obtained in the MQB structure.