Naoki Chinone

Transverse mode stabilized Al x Ga 1-x As injection lasers with channeled-substrate-planar structure

A built-in passive waveguide mechanism is introduced in Al x Ga 1-x As injection lasers by growing planar double heterostructure (DH) layers on a grooved GaAs substrate. The lasing mode is confined to the channel region due to excess absorption loss outside the channel. Stable fundamental mode oscillation is achieved up to twice the threshold current for a channel width of 5-8 \mu . Undesirable lasing behavior usually induced by transverse mode instability, such as nonlinear kinks in the light output versus current characteristics, are significantly reduced in the present lasers. The dc threshold current is 40-90 mA at room temperature. Median lifetime of 780 hours has been obtained during preliminary aging tests at a heat sink temperature of 70°C.

Longitudinal‐mode behaviors of mode‐stabilized AlxGa1−xAs injection lasers

Lasing spectra of a transverse‐mode‐stabilized AlGaAs laser of a channeled‐substrate planar structure have been investigated. These lasers, which oscillate in the fundamental transverse mode, reproducibly operate in a single longitudinal mode. In addition, their linewidth is as narrow as or smaller than 30 MHz when the injection current is ∼1.2 times above threshold. The intensity distribution and excitation dependence of a nonlasing longitudinal mode have been found to be more complicated than expected from a simple theory: sizable dips have been observed in the envelope function, and nonlasing modes have been found to decrease as the injection current is increased above threshold. Furthermore, hysteresis has invariably been observed in the lasing‐wavelength–vs–device‐temperature (or dc current) characteristics. These behaviors are believed to reflect a slightly inhomogeneous nature of the gain spectrum because of a finite thermalization time of injected carriers, as discussed recently by Yamada and Suem...

Linewidth enhancement factor in strained quantum well lasers

The linewidth enhancement factor alpha of strained quantum-well lasers is analyzed by the k-p perturbation method using the effective-mass approximation. It is found that the alpha factor in a strained In/sub 0.80/Ga/sub 0.20/As/InP quantum-well (QW) laser with 1.9% biaxial compression is less than 1.5. For a strained QW laser with p-type modulation doping (MD) of 5*10/sup 18/ cm/sup -3/, the alpha factor is as small as 0.8. It is also demonstrated that the spectral linewidth and wavelength chirping in the strained MD QW laser are significantly less than those in conventional bulk and QW lasers.<<ETX>>

Nonlinearity in power-output--current characteristics of stripe-geometry injection lasers

The origins and behaviors of kinks in power‐output–injection‐current (I‐L) curves of stripe‐geometry lasers are theoretically investigated. Laser output power is calculated as a function of injection current by solving the carrier diffusion equation and Maxwell’s equation. Transverse modes along the junction plane are assumed to be guided by the injected‐carrier‐induced gain profile. At low current densities, it is shown that the gain profile is nearly parabolic, resulting in the transverse mode very close to the lowest Hermite‐Gaussian distribution. However at high current densities the gain profile is deformed by the stimulated recombination of carriers near the center of the stripe. The resultant mode becomes deformed and penetrates into the low‐gain or lossy region. Consequently the mode gain is reduced, and the power saturation (kink) appears in the I‐L curves. If there exists an asymmetry in the injection current density profile, it is shown that the optical intensity peak moves along the junction plane and the beam direction shifts from the normal to the laser facets with the increase of the current density. Such theoretical results are qualitatively in good agreement with recent experimental observations and demonstrate that kinks originate from the gain profile deformation and the resultant mode deformation. Investigating the dependence of the output power at which a kink appears on various device parameters such as the stripe width, the amount of current spreading, and the degree of asymmetry, we conclude that the scatter of the output power experimentally observed is caused by the small fluctuations of such device parameters.The origins and behaviors of kinks in power‐output–injection‐current (I‐L) curves of stripe‐geometry lasers are theoretically investigated. Laser output power is calculated as a function of injection current by solving the carrier diffusion equation and Maxwell’s equation. Transverse modes along the junction plane are assumed to be guided by the injected‐carrier‐induced gain profile. At low current densities, it is shown that the gain profile is nearly parabolic, resulting in the transverse mode very close to the lowest Hermite‐Gaussian distribution. However at high current densities the gain profile is deformed by the stimulated recombination of carriers near the center of the stripe. The resultant mode becomes deformed and penetrates into the low‐gain or lossy region. Consequently the mode gain is reduced, and the power saturation (kink) appears in the I‐L curves. If there exists an asymmetry in the injection current density profile, it is shown that the optical intensity peak moves along the junction p...

Tunable DFB laser with a striped thin-film heater

The authors propose a very simple tunable laser with a striped thin-film heater. The wavelength of this laser changes with a sensitivity of 3.2 nm/W to the input heating power. This laser can be continuously tuned over a range of 4 nm while maintaining an optical power of 20 mW and with a linewidth of less than 2.5 MHz. When this laser is mounted on a module, its 90% response time is 6 ms, which is fast enough for use as a local oscillator in several applications.<<ETX>>

A two-dimensional device simulator of semiconductor lasers

Abstract A two-dimensional simulator for aid in designing semiconductor lasers is developed. Poissons equation and the current continuity equations for electrons and holes as well as the wave equation and rate equation for photons are numerically solved. Heterojunctions and carrier degeneracy are rigorously treated, and analytical results on channeled-substrate-planar lasers are presented to demonstrate the simulator. Reasonable agreement is found between calculated and experimental results, and calculated results clarify precisely the operation mechanism of semiconductor lasers. The present work enables computer simulation for the first time to be a practical design aid in research and development of various kinds of semiconductor lasers.

Ultrahigh relaxation oscillation frequency (up to 30 GHz) of highly p‐doped GaAs/GaAlAs multiple quantum well lasers

We have demonstrated a relaxation oscillation frequency (fr) of up to 30 GHz in highly p‐doped (Be=1×1019 cm−3) GaAs/GaAlAs multiple quantum well (MQW) lasers grown by molecular beam epitaxy. This is the highest fr achieved at room temperature for III‐V semiconductor lasers. The high fr is attained by the large differential gain in the p‐doped MQW structure having a low threshold electron density resulted from the excess hole density in addition to the quantum size effect.

Effects of lateral mode and carrier density profile on dynamic behaviors of semiconductor lasers

Dynamic behaviors of the semiconductor lasers have been investigated both theoretically and experimentally. A single-mode rate equation, which takes account of the lateral mode profile and the carrier density profile, has been solved numerically. Effects of the carrier and lateral mode confinement have been clarified. The lateral mode deformation in lasers without a built-in mode confinement structure greatly enhances the relaxation oscillations. In lasers whose stripe width is narrower than \sim10 \mu m, the carrier diffusion is found to play an important role in suppressing the relaxation oscillations, especially for lasers without a lateral carrier confinement structure. On the other hand, the fraction of the spontaneous emission going into the lasing mode is significant for lasers with a lateral carrier confinement structure. The slow increase of the laser output at the transient is confirmed to be due to the carrier diffusion.

Corrugation-pitch modulated MQW-DFB lasers with narrow spectral linewidth

Narrow spectral linewidth lasers are developed for optical coherent transmission systems. To obtain a narrow spectral linewidth, a CPM (corrugation-pitch modulated) structure is introduced into 1200- mu m-long MQW-DFB (multi-quantum well distributed feedback) lasers. The CPM structure effectively suppresses the axial spatial hole burning effect and stabilized single-mode spectrum at high output powers. A spectral linewidth of 170 kHz was achieved at an output power of 25 mW. Details of corrugation fabrication method that makes the CPM structure possible are described. >

Novel method to fabricate corrugation for a λ/4‐shifted distributed feedback laser using a grating photomask

A novel method was developed to fabricate corrugation for a λ/4‐shifted distributed feedback (DFB) laser. Mechanically ruled grating patterns were transferred photolithographically to the surface of an InP substrate. The resultant λ/4‐shifted DFB laser operated in a single longitudinal mode at the Bragg wavelength.