Loss coefficient for amplified luminescence of laser diode arrays

Abstract

A system of radiative transfer equations is used to calculate the loss coefficient for amplified luminescence fluxes propagating along and transverse to the cavity axis in the active layer of high-power laser diode arrays taking the spreading of charge carriers in the cladding and contact layers of InGaAs/GaAs/AlGaAs heterostructures into account. It is shown that the spreading of charge carriers leads to a significant change in the amplified luminescence flux which can contribute up to 18% to the lasing threshold of these laser diode arrays. The calculated loss coefficients can greatly simplify the determination of the amplified luminescence fluxes in laser diode arrays with an error of less that 16% and can be used to determine how much the amplified luminescence affects the power and dynamic characteristics of diode arrays.Introduction. High-power laser diode arrays (LDAs) are coming into ever wide use as compact, highly efficient sources of optical excitation for solid state lasers [1][2][3]. Reducing the energy demand by these emitters requires optimization of the parameters of the LDAs, as well as of the solid state lasers. The power of modern LDAs used as pumps is approaching 80-150 W [1, 4]. These relatively high LDA powers have been achieved by substantial increase in the length of the cavities and the total widths of the heterostructure lasing elements. In most cases of practical interest, the LDA is characterized by a relatively high area of the active layer of the laser heterostucture. Thus, it is to be expected that, in accordance with [5-10], intense fluxes of amplified luminescence should develop in the active layers of LDAs; these result in an increase in the threshold and a reduction in the laser output power. It has been shown [5, 6, 8-10] that the AL fluxes for single laser diodes (with a single emitting region, or strip contact) can be analyzed by introducing an AL loss coefficient α lum determined from the balance between emission, amplification, and absorption of spontaneous emission ]11]. The value of α lum depends on many factors, in particular, on the composition of the active layer, the geometry of the laser structure, the excitation conditions, etc. Thus, as opposed to the loss coefficient for the laser emission, finding α lum is a rather complicated task in most cases of practical importance. This paper deals with the determination of the loss coefficient for AL produced in the active layer of highpower LDAs with as many as a few hundred regions. The resulting values of α lum can be used to estimate how much AL affects the threshold, dynamic, and power properties of LDAs and to determine methods for further improvement in the characteristics of LDAs and of diode pumped solid state lasers.Propagation of Fluxes of Amplified Luminescence in LDAs. The AL characteristics of concern for the parameters of LDAs (output wavelengths 940-980 nm) used to pump solid state erbium lasers are studied here. These LDAs are generally based on InGaAs/GaAs/AlGaAs heterostructures with two quantum-dimension...

Amplified luminescence in InGaAs/AlGaAs laser diode arrays at high pump levels

“…Fluxes of amplified luminescence (AL) formed in the active layer of powerful laser diode arrays (LDAs) increase the threshold and decrease the power of the generation [1,2]. It was shown [1] that the characteristics of AL in an LDA can be analyzed in a model approximation that takes into account fluxes of AL propagated along two principal directions, i.e., the cavity axis Oy and the axis perpendicular to it Ox (parallel to the LDA cavity mirrors).…”

“…It was shown [1] that the characteristics of AL in an LDA can be analyzed in a model approximation that takes into account fluxes of AL propagated along two principal directions, i.e., the cavity axis Oy and the axis perpendicular to it Ox (parallel to the LDA cavity mirrors). In terms of this approach, AL loss coefficients α lum y and α lum x are introduced for each of the AL fluxes [1,3]. Coefficients α lum y and α lum x were defined at pump currents I that did not exceed the threshold value I thr [1].…”

“…In terms of this approach, AL loss coefficients α lum y and α lum x are introduced for each of the AL fluxes [1,3]. Coefficients α lum y and α lum x were defined at pump currents I that did not exceed the threshold value I thr [1]. However, according to the literature [2], the AL flux integrated over the spectrum along axis Ox of the LDA active layer S x does not reach saturation near the generation threshold with increasing pump level but continues to increase even for I > I thr .…”

“…Experimental results [2] suggested that this increase of S x was due mainly to a decrease of loss coefficient α lum x for the LDA with increasing I > I thr . This was explained by an increase of the concentration of non-equilibrium charge carriers in passive regions of the LDA as a result of current leakage in the heterostructure layers [1]. All this stimulated the development of methods for determining α lum x at pump currents above the threshold value.…”

“…from the literature [1]. The square of the matrix element of interband optical transitions ⏐ M ⏐ 2 = 3.41⋅10 -49 kg 2 ⋅m 2 /s 2 for the InGaAs active layer was calculated using published data [5].…”