Nonuniform Current Injection Research Articles

Optimum asymmetric mirror facet structure for high-efficiency semiconductor lasers

A design theory for asymmetric mirror facet structure lasers that takes into account the spatial hole burning (SHB) effect along the cavity is presented. It is shown that the SHB effect reduces the external quantum efficiency in asymmetric mirror facet structure lasers, and the front facet reflectivity has an optimum value depending on the internal loss for high-efficiency operation. A slope efficiency of more than 50% has been obtained in lasers based on the new design theory. It is noted that nonuniform current injection is one of the most useful methods for increasing the external quantum efficiency, which is reduced by the SHB effect. >

Lasing characteristics for four-section MQW-DBR laser

A MQW-DBR laser with two active sections and low tuning efficiency has been developed. The device showed excellent lasing characteristics: a low threshold current of 10 mA, a high slope efficiency of 0.26 mW/mA, and a narrow linewidth of 280 kHz at P/sub out/=15 mW. A red-shift carrier-induced FM response was obtained by nonuniform current injection to two active sections. A flat FM response with wide bandwidth (>2 GHz) was confirmed. The linewidth broadening due to wavelength tuning was suppressed through the reduction of tuning efficiency. A continuous tuning range of 0.8 nm was observed while maintaining the linewidth below 4 MHz. >

Effects of nonuniform current injection in GaInAsP/InP vertical- cavity lasers

We systematically measured the active-area dependence of the threshold current density of GaInAsP/InP vertical-cavity lasers at various temperatures. The threshold current density was found to increase monotonically with increasing active area, with the effect becoming more pronounced at higher temperature. This phenomenon is due to nonuniform current injection into the active region.

Superconducting millimeter wave oscillators

The integrated superconducting mm wave oscillator have been designed and experimentally investigated. It consists of Flux Flow oscillator (FFO), coupling section and detector junction with tuned out capacitance. Oscillator is long Josephson junction with nonuniform current injection shunted by Mo resistor to obtain dissipation parameter α ∼ 0.5. Coupling section is designed as microstrip quarter-wave three step transformer with dc-block between oscillator and detector. All refractory material integrated circuits have been fabricated on the base of high quality Nb-AlOx-Nb junctions. The oscillations in the ranges 75 – 260 GHz have been experimentally observed. The values of the generated power have been calculated from the amplitudes of the quasiparticle and Shapiro steps on the I-V curve of the detector junctions. The detected power levels higher than 0.1 μW have been obtained. The linewidth value of FFO not more than 1 MHz has been experimentally estimated.

A self-consistent model of a nonplanar quantum-well periodic laser array

An analysis of a nonplanar semiconductor periodic laser array is carried out using a self-consistent model that successfully explains the experimentally observed efficiencies and output optical patterns. This model takes into account the two-dimensional injected current distribution coupled with the optical intensity profile and gain variation from the mesa to the groove. The optical field distribution of the nonplanar laser array is treated as a linear combination of the optical modes in the mesas, grooves, and bends using the effective index method. Numerical results show the multimode operation due to spatial hole burning, the near-field patterns affected by the nonuniform current injection, and the competition of available carriers among the modes of neighboring waveguides.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spectral linewidth of DFB lasers including the effects of spatial holeburning and nonuniform current injection

An analytic expression for the linewidth of distributed-feedback (DFB) lasers is derived. Local fluctuations in carrier density are shown to provide a significant contribution to laser linewidth in the presence of spatial holeburning. In a single-electrode DFB laser the effect can be avoided by careful optimization of the kl-product, but for a multielectrode DFB laser the linewidth can also be reduced by adjusting the injected current profile to compensate for spatial holeburning. Numerical results for a three-electrode lambda /4-shifted DFB laser are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of oscillation characteristics of separated-electrode DFB laser diodes

The oscillation characteristics of separated-electrode distributed feedback (DFB) lasers are analyzed by a numerical approach. In the calculation, coupled-mode equations are used including the carrier-density nonuniformity along the laser axis, which is introduced by the spatial hole burning and/or the nonuniform current injection. When the center section of a DFB laser, with three equally separated electrodes, is more strongly pumped than the side sections, high performance is achieved: the mode stability is maintained in the high-power state, resulting in a narrow linewidth. This is because the spatial hole burning is compensated by the larger current injection into the center region. The wide tunable range is also obtained under this bias condition. >

Three-electrode DFB wavelength tunable FSK transmitter at 1.53 μm

A three-electrode DFB laser using nonuniform current injection has been shown to present excellent FM response sensitivity (0.7GHz/mA) and bandwidth (&gt; 1 GHz) together with a broadband wavelength continuous tuning capability (Δλ= 2nm, 258 GHz) while maintaining a narrow linewidth (δv ∼ 20 MHz). This structure, easy to fabricate, appears very promising for CMC networks and transmission.

Tunable, narrow-linewidth and high-power λ/4-shifted DFB laser

A 1.5μm-range λ/4-shifted DFB laser with a l.2 mm-longcavity and three electrodes has been fabricated. The lasing wavelength can be tuned electrically over a 1.9 nm range, maintaining the linewidth below 900 kHz and a constant output power of 20 mW. The minimum linewidth of 500 kHz is achieved by nonuniform current injection.

A travelling-wave rate equation analysis for semiconductor lasers

A travelling-wave rate equation model for the investigation of the transient effects in a semiconductor laser is presented. The model includes the spatial dependence of the photon and excess carrier densities and may be applied to lasers with non-uniform current injection and inhomogeneous material properties. Details of the numerical algorithm which enables the equations to be solved are given. Numerical results show that unpumped regions and defects inside a laser can shorten the optical pulses obtained by gain-switching.

Passive mode locking of buried heterostructure lasers with nonuniform current injection

In this letter we report on a novel method to passively mode lock a semiconductor laser. We present experimental results of GaAlAs buried heterostructure semiconductor laser with a split contact coupled to an external cavity. The split contact structure is used to introduce a controllable amount of saturable absorption which is necessary to initiate passive mode locking. Unlike previous passive mode locking techniques, the method presented does not rely on absorption introduced by damaging the crystal and is consequently inherently more reliable. We have obtained pulses with a full width at half-maximum of 35 ps at repetition frequencies between 500 MHz and 1.5 GHz.

Effect of longitudinal variations in current injection and carrier concentration in laser diodes

The effects of nonuniform current injection along the length of a semiconductor laser are investigated using multiple segmented stripe contact lasers. The results of the experiments are analyzed with a model for which the carrier concentration, gain, and photon density are functions of position. From the model, it was determined that nonuniform current injection caused large variations in the optical field within the laser, and the field produced a redistribution of electrical carriers in the active region. The nonlinearities in the light versus current measurements were explained by the redistribution of carriers as the optical field changed.