Toshikazu Mukaihara

Polarization control of vertical-cavity surface emitting lasers using a birefringent metal/dielectric polarizer loaded on top distributed Bragg reflector

A novel polarization control method using a birefringent metal/dielectric (semiconductor) polarizer has been proposed for the purpose of controlling the polarization state of vertical-cavity surface-emitting lasers (VCSELs). The proposed structure provides a phase difference for two orthogonal polarization states, resulting in reasonably large reflectivity difference in two polarizations. We have experimentally demonstrated the polarization control InGaAs-GaAs VCSELs while maintaining a low threshold current density of 660 A/cm/sup 2/. A predominant polarization state along the designed orientation is obtained up to two times the threshold. >

A Novel Short-Cavity Laser with Deep-Grating Distributed Bragg Reflectors

We have proposed a novel short-cavity laser with deep-grating distributed Bragg reflectors (DBRs). We monolithically fabricated a 0.98 µm InGaAs/AlGaAs device and 1.55 µm GaInAsP/InP device using electron beam lithography and a reactive ion beam etching technique. The lasing operation of both devices was achieved at room temperature. From a comparison of the threshold current from the experimental result with that from the theoretical result, the reflectivity of formed DBRs was estimated to be less than 30%. The theory also predicts that the ideal DBR exhibits a high reflectivity over 97% even with 3 periods of grating. It achieves lasing operation with a threshold current less than 100 µA using a cavity shorter than 10 µm. This high performance is realized by reducing the surface roughness and damage to etched sidewalls and improving the reflectivity of the DBR.

Engineered polarization control of GaAs/AlGaAs surface-emitting lasers by anisotropic stress from elliptical etched substrate hole

The engineered polarization control of surface emitting (SE) lasers, based on the observed evidence of the polarization determination, is reported. Thermally stressed epitaxial layers including an active region are made anisotropic by an elliptically etched substrate structure. This stress causes an anisotropy in optical gain of the active region. The polarization control has been demonstrated with about 80% reproducibility in etched-well-type surface emitting (SE) lasers by employing a thick gold film or a polyimide as a stress-enhancing material.<<ETX>>

An InGaAs-GaAs vertical-cavity surface-emitting laser grown on GaAs(311)A substrate having low threshold and stable polarization

We have fabricated an InGaAs-GaAs vertical-cavity surface-emitting laser (VCSEL) grown on a GaAs(311)A substrate by molecular beam epitaxy (MBE) and demonstrated continuous wave operation at room temperature. A threshold current density of 80 A/cm/sup 2//well and very stable polarization characteristics up to 2.7 times the threshold were achieved. The polarization state with the highest optical intensity was oriented along the [2~33] direction, which is the crystallographic axis exhibiting the maximum gain. An extinction ratio of more than 12.7 dB was obtained between two orthogonal polarization states. The high and anisotropic gain of a (311)A-oriented VCSEL will drastically improve the device performance by optimization and process engineering.

Wavelength control of vertical cavity surface-emitting lasers by using nonplanar MOCVD

We present a novel approach of on-wafer wavelength control for vertical cavity surface-emitting lasers (VCSELs) using nonplanar metalorganic chemical vapor deposition. The resonant wavelength of 980 nm VCSELs grown on a patterned substrate can be controlled in the wavelength range over 45 nm by changing the size of circular patterns. A multi-wavelength VCSEL linear array was fabricated by using this technique. The proposed method will be useful for multi-wavelength VCSEL arrays as well as for the cancellation of wavelength nonuniformity over a wafer.<<ETX>>

Lasing characteristics of low-threshold oxide confinement InGaAs-GaAlAs vertical-cavity surface-emitting lasers

Some lasing characteristics of index-guided InGaAs-GaAlAs vertical-cavity surface-emitting lasers (VCSELs) with a native oxide confinement structure, which produced a low threshold current of 70 /spl mu/A, are presented. It was found that nonradiative recombination was reduced and the estimated surface recombination velocity was almost negligible. The oxidation process was uniform to produce low threshold devices while the oxidation rate was dependent on the doping or composition of DBRs.<<ETX>>

Excess intensity noise originated from polarization fluctuation in vertical-cavity surface-emitting lasers

We have observed an excess-intensity noise that is attributed to polarization fluctuations of InGaAs-GaAs vertical-cavity surface-emitting lasers (VCSELs). It was observed, for the first time, that the intensity noise increased remarkably by the polarization fluctuation even when the single transverse mode operation was maintained. This result indicates that it is necessary to control the polarization state of VCSELs as well as control the transverse modes for low-noise operations.<<ETX>>

A Novel Birefringent Distributed Bragg Reflector Using a Metal/Dielectric Polarizer for Polarization Control of Surface-Emitting Lasers

We propose a novel polarization control structure in vertical cavity surface-emitting lasers using a birefringent metal/dielectric polarizer terminating a distributed Bragg reflector (DBR). Polarization-dependent reflectivity at the resonant wavelength is theoretically predicted by adjusting the phase condition in the DBR. An experimental result shows a reflectivity difference for two polarization states. The possibility of polarization control as well as polarization switching is suggested.

Recent advances in DFB lasers for ultradense WDM applications

State-of-the-art distributed feedback (DFB) laser modules integrated with a wavelength monitor are presented that provide excellent wavelength stability. By adopting unique and compact configuration, wavelength deviations of as small as a few picometers have been achieved. The laser modules are improved also in the scope of high power, high reliability, and wavelength tunability. Reliability test results of the DFB laser diodes and modules confirm a sufficiently long lifetime of more than 25 years and a small wavelength drift of less than /spl plusmn/3 pm. The developed laser modules are fully applicable to ultradense wavelength-division multiplexing applications with the current narrowest channel spacing of 25 GHz.

Polarization control of vertical-cavity surface-emitting lasers by a birefringent metal/semiconductor polarizer terminating a distributed Bragg reflector

We propose a polarization controlled vertical-cavity surface-emitting laser (VCSEL) using a birefringent metal/semiconductor polarizer on a distributed Bragg reflector. Theoretically, we found that the proposed concept can provide an extremely large polarization selectivity at the resonant cavity wavelength by adjusting the phase condition between two polarization states. Experimentally, we have demonstrated a 0.98 /spl mu/m InGaAs/GaAs VCSEL with an Au/GaAs polarizer exhibiting a fairly good polarization control and maintaining low thresholds.