Epitaxially-stacked multiple-active-region 1.55μm lasers for increased differential efficiency

Abstract

Semiconductor lasers emitting at 1.55 μm with external differential efficiencies >1 have been created by monolithically connecting several active regions in series within a single optical waveguide. This is accomplished by epitaxially stacking a number of p–i–n multiquantum well active regions with intermediate n++–p++ back diodes, which enable the entire terminal current to flow through each active region stages in series. Such lasers should also improve the impedance match as well as provide for low-noise, high-efficiency microwave links.

>100% output differential efficiency 1.55-μm VCSELs using submonolayer superlattices digital-alloy multiple-active-regions grown by MBE on InP

“…These MAR VCSELs with DAAR, when compared to an identical design using conventional analogalloy active regions [2], demonstrate comparable performance in terms of output differential efficiency and better performance in terms of voltage and threshold currents. Furthermore, 3-stage MAR edge-emitting lasers with DAAR, fabricated to evaluate active region parameters, performed similarly to previously published MAR edgeemitting lasers with analog-alloy active regions [5]. 3-stage MAR edge-emitting lasers with DAAR exhibited injection efficiencies, Z i ; of $275% and optical losses, a i ; of $28 cm À1 , while those grown with analog-alloy active regions had Z i ¼ 233% and a i ¼ 38 cm À1 [5].…”

“…Detailed analysis of the scaling properties of MAR devices can be found in Refs. [1,2,5]. To realize high performance MAR VCSELs, high-quality active regions must be developed.…”

Scaling of the photon noise in semiconductor cascade lasers

“…Since impedance is inversely proportional to area, the impedance of each gain We also make the reasonable assumption that the output power of a cascade laser increases linearly with the increase in the total volume of the laser cavity. This implies that both the output power and the cavity volume scale as N α , where α = 1 for bipolar tunnel diode cascade lasers and 0 for unipolar quantum cascade lasers and bipolar segmented waveguide cascade lasers [3][4][5][6]. Since the output power of an N -stage cascade laser is given by the expression [2-6, 10]…”

“…Scaling method (a) is used in bipolar tunnel diode cascade and unipolar quantum cascade lasers, and scaling method (b) is used in bipolar segmented waveguide cascade lasers [2][3][4][5]10]. In method (a), the total impedance of all the gain stages scales as N Z d , where Z d is the impedance of a single gain stage.…”

“…Figure 1 shows a bipolar segmented waveguide cascade laser [3] in which a conventional laser waveguide is segmented into smaller sections that are connected electrically in series. Figure 2 shows a bipolar tunnel diode cascade laser [4,5] in which multiple PN junctions are connected electrically in series through reversed biased tunnel diodes. Figure 3 shows a unipolar intersubband quantum cascade laser [2].…”