Nobuhiko Nishiyama

Strongly Index-Coupled Membrane BH-DFB Lasers With Surface Corrugation Grating

We realized strongly index-coupled membrane buried-heterostructure (BH) distributed-feedback (DFB) lasers fabricated by electron-beam lithography, CH4/H2 reactive-ion etching, and regrowth by organometallic vapor-phase epitaxy, using surface corrugation DFB. First, we fabricated narrow stripe membrane BH-DFB lasers with surface corrugation for stable single-mode operation. Under optically pumped room-temperature continuous-wave (RT-CW) operation, a wide stopband width of 68 nm was observed in spite of the narrow stripe width of 0.6 mum. The corresponding index-coupling coefficient of 2950 cm-1 is over two times larger than that of a flat-surface (conventional) membrane BH-DFB laser with a stripe width of 2.0 mum. In addition, we fabricated a short-cavity membrane DFB laser with a surface corrugation structure. A threshold optical pump power of as low as 0.34 mW was realized for a 2.0-mum-wide and 80-mum-long device under RT-CW conditions.

High-temperature operation up to 170/spl deg/C of GaInNAs-GaAs quantum-well lasers grown by chemical beam epitaxy

High-temperature pulsed operation of GaInNAs-GaAs double-quantum-well lasers grown by chemical beam epitaxy has been demonstrated for the first time. The lasing wavelength was from 1.20 to 1.27 /spl mu/m with different composition at room temperature. The highest lasing operation temperature up to 170/spl deg/C and a high characteristic temperature of 270 K were obtained for 300-/spl mu/m-long lasers at 1.2 /spl mu/m.

GaInAsP/InP Membrane Lasers for Optical Interconnects

In this paper, the state-of-the art of long-wavelength GaInAsP/InP membrane semiconductor lasers, one of the most promising candidate light sources for optical interconnects and on-chip optical wiring between large-scale integrated circuits, is described. After an extensive review of research activities focused on laser preparation on either Si or Si-on-insulator substrate, the findings of our recent research activities on low power consumption lasers are presented. Specifically, our interest was set on the low-damage fabrication of strongly index-coupled grating, which is generally opted forDFB and distributed reflector (DR) lasers consisting of wire-like active regions, as well as of high index-contrast membrane waveguides. A submilliampere threshold current and a differential quantum efficiency close to 50% from the front facet were achieved in the case of the DR laser. On the other hand, a lateral current injection (LCI) structure, which can be combined with the membrane laser, was adopted for the realization of an injection-type membrane laser. The successful continuous wave operation of LCI lasers, prepared on a semiinsulating InP substrate, was achieved with moderately low threshold current at room temperature.

Multi-oxide layer structure for single-mode operation in vertical-cavity surface-emitting lasers

We propose a novel vertical-cavity surface emitting laser (VCSEL) with Al(Ga)As multi-oxide layer (MOX) structure for the purpose of enlarging window aperture maintaining single transverse mode operation. We have fabricated an InGaAs-GaAs VCSEL with the proposed MOX structure formed on GaAs (311)B substrate. We have performed a numerical simulation to investigate single-mode behavior of the proposed structure and showed a possibility of single-mode VCSELs with a large active area. We have fabricated an 11-/spl mu/m current aperture 960-nm wavelength VCSEL with this MOX structure. The threshold current and voltage were 1.0 mA and 2.0 V, respectively, which are comparable to those of conventional oxide VCSELs. In 8-/spl mu/m aperture, single-mode operation was maintained with a driving current up to four times the threshold.

Lasing characteristics of InGaAs-GaAs polarization controlled vertical-cavity surface-emitting laser grown on GaAs [311] B substrate

We have demonstrated an oxide confinement polarization controlled vertical-cavity surface-emitting laser (VCSEL) grown on a GaAs [311]B substrate. The polarization state was well controlled along the [2~33] crystal direction due to an anisotropic gain in the [311]B plane. We fabricated a small oxide aperture VCSEL with a threshold of 260 /spl mu/A and realized single-transverse mode and single-polarization operation for the first time. The sidemode suppression ratio (SMSR) was 35 dB and the orthogonal polarization suppression ratio (OPSR) was 25 dB. In addition, we have measured polarization and transverse mode characteristics of multi- and single-transverse mode devices under high-speed modulation. In the multimode device of 12 /spl mu/m/spl times/12 pm oxide aperture, we have achieved stable polarization operation of over 25-dB OPSR up to 10 Gb/s and have observed no power penalty due to polarization instability under 2.5-Gb/s pseudorandom modulation. The single-mode device showed stable single-transverse mode and polarization under the modulation conduction up to 5 GHz of sinusoidal modulation. SMSR and OPSR were over 30 and 10 dB, respectively.

Lateral current injection GaInAsP/InP laser on semi-insulating substrate for membrane-based photonic circuits

A room-temperature pulsed operation was demonstrated using lateral current injection-type lasers composed of a 400-nm-thick GaInAsP core layer with compressively strained 5 quantum wells. A threshold current of 105 mA and corresponding density of 1.3 kA/cm(2) (260 A/cm(2) per well) were obtained with the stripe width of 5.4 microm and the cavity length of 1.47 mm. A fundamental transverse mode operation was obtained with the narrower stripe device of 2.0 microm and the cavity length of 805 microm, while the threshold current and corresponding density were 49 mA and 3.0 kA/cm(2), respectively.

107-mW low-noise green-light emission by frequency doubling of a reliable 1060-nm DFB semiconductor laser diode

We have generated 107-mW green-light emission by frequency doubling of a reliable 1060-nm distributed feedback (DFB) laser diode using a periodically poled MgO-doped lithium niobate waveguide in the most compact single-pass configuration. The green power variation is lower than 1% at frequencies below 82 kHz. The relative intensity noise of -150 dB/Hz has been measured at 100 MHz. We also report 5000-h life-test results of 1060-nm DFB lasers at 80/spl deg/C.

Analysis and fabrication of microaperture GaAs-GaAlAs surface-emitting laser for near-field optical data storage

We have proposed a microaperture vertical cavity surface-emitting laser (VCSEL) for use in near-field optical data storage. We carried out the near-field analysis of microaperture VCSEL using two-dimensional (2-D) finite element method. We calculated the distribution of optical near-field generated near a microaperture, and showed that the spot size is potentially smaller than 100 nm, which is less than wavelength by a factor of 8. We fabricated a VCSEL loaded by an Au film on the top surface for blocking the emitting light and formed a subwavelength-size aperture using focused ion beam (FIB) etch through this film. Single-mode operation was obtained for a microaperture VCSEL with 3-/spl mu/m square active region. The differential quantum efficiency was increased by a factor of 3 in comparison with that before forming a 400-nm square aperture. We estimated the power density of light radiated from a 400-nm square aperture to be 0.17 mW//spl mu/m/sup 2/. In addition, we measured the near-field distribution of a 200-nm square aperture VCSEL by using a scanning near-field microscope.

Dynamic behavior of an all-optical inverter using transverse-mode switching in 1.55-/spl mu/m vertical-cavity surface-emitting lasers

An all-optical inverter using transverse-mode switching of a 1.55-/spl mu/m vertical-cavity surface-emitting laser is demonstrated. When an external light is injected to a first high-order mode, the output power of the fundamental mode is strongly suppressed due to injection locking resulting in a large extinction ratio of over 20 dB. Waveform inversion is demonstrated for the input signal of a 5-GHz sinusoidal wave.

GaInAsP/InP lateral-current-injection distributed feedback laser with a-Si surface grating.

We fabricated a novel lateral-current-injection-type distributed feedback (DFB) laser with amorphous-Si (a-Si) surface grating as a step to realize membrane lasers. This laser consists of a thin GaInAsP core layer grown on a semi-insulating InP substrate and a 30-nm-thick a-Si surface layer for DFB grating. Under a room-temperature continuous-wave condition, a low threshold current of 7.0 mA and high efficiency of 43% from the front facet were obtained for a 2.0-μm stripe width and 300-μm cavity length. A small-signal modulation bandwidth of 4.8 GHz was obtained at a bias current of 30 mA.