Near-diffraction-limited coherent emission from large aperture antiguided vertical-cavity surface-emitting laser arrays

Abstract

We demonstrate that in-phase mode operation with a near-diffraction-limited beam can be realized in large aperture ͑up to 100 elements͒ antiguided vertical-cavity surface-emitting laser ͑VCSEL͒ arrays. A selective etching process with two-step metalorganic chemical vapor deposition is used for fabrication of the antiguided VCSEL array structures. Modal discrimination is enhanced by intentionally choosing a GaAs cap thickness so as to introduce suitable loss to array interelement regions. Far field patterns indicate in-phase mode operation from both triangular and rectangular geometry antiguided VCSEL arrays, which is in good agreement with theory. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1640799͔Coupled two-dimensional vertical-cavity surfaceemitting arrays are promising as high power ͑more than 10 mW͒ coherent light sources for many applications such as telecommunications, printing, data storage etc. In addition, their two-dimensional periodicity of the gain and index make them ideal sources with which to study the properties of active photonic lattices.1 In the past, much effort has been directed towards realizing coherent emission from phaselocked vertical-cavity surface-emitting laser ͑VCSEL͒ arrays. However, previous work has shown that phase-locked VCSEL arrays tend to lase in the highest-order, out-of-phase, transverse mode. Mode discrimination is also low among various transverse array modes, and generally results in a mixture of high-order modes reaching laser threshold.2 Continuous wave ͑cw͒ operation of 10ϫ10 VCSEL arrays that utilized a metal grid defined structure to insure single higherorder mode operation has been reported. 3 Larger aperture (ϳ138 mϫ138 m) coherent 20ϫ20 VCSEL arrays have been reported previously using photon pumping, and they exhibited a four-lobe, multimode, far-field pattern.4 This behavior is characteristic of evanescent wave coupling in weakly positive index guided or gain guided arrays. 5 To make ''in-phase-mode-like emission,'' external phase shifters are required, although the result is still a relatively broad beam that is indicative of multimode operation.6 Thus, stable, high power, diffraction-limited beam operation has not been realized.Compared to weak evanescent coupling in positive index guided arrays, antiguided structures are attractive due to the strong leaky-wave coupling between each element in the array. What is more, modal discrimination is also enhanced by array mode dependent lateral radiation loss. Thus, by properly choosing the index step and width of the coupling region, the in-phase array mode is favored to lase. Moreover, antiguided arrays are less vulnerable to thermal lensing and gain spatial hole burning ͑GSHB͒ because of the strong built-in index step, which leads to stable beam operation at high output power. 7 In 1999 Serkland et al. reported the observation of in-phase mode emission from two leaky-wave coupled VCSELs. 8 Later, in 2000, diffraction-limited emission from two-dimensional ͑2D͒ (4ϫ4) leaky-wave coupled VCSEL arrays 9,10...

Two-Dimensional Antiguided Vertical Cavity Surface Emitting Laser Arrays With Reflecting Boundary

“…A 1-D transfer matrix method can be used to evaluate loss due to mirror reflection and metal absorption. The calculated loss is changing periodically with GaAs cap thickness [3]. Our previous publication shows that if the cap thickness is around 45 nm, higher loss can be introduced only to the interelement regions (terminated with Ti).…”

“…The lateral effective index step Δn for antiguiding can be achieved in the VCSEL by intentionally shifting the optical cavity resonance across the structure according to the effective index theory [21]: Δn/n = Δλ/λ. The effective index method has been used to predict the lateral resonance condition for 2-D VCSEL arrays in [2], [3], and [22]. A detailed theoretical and experimental analysis [6], [19] has shown the resonant antiguided 5 × 5 VCSEL array to provide single-mode lasing for pump current 4J th .…”

“…Inphase mode emission has been reported from coupled VCSELs [1] and from 2-D arrays employing antiguided VCSEL elements [2]. Near-diffraction-limited beam operation was reported from large aperture (100 elements) antiguided VCSEL arrays [3]. In antiguided arrays (see Fig.…”

Leaky defect modes of two-dimensional VCSEL arrays

“…In VCSEL design, we apply mirror absorption losses to the area outside the defect core region to enhance modal discrimination. This technique was reported previously to fabricate metal grid VCSEL arrays, which operate in an out-of-phase array mode [8]. In our design, the 2-D lattice is constructed so that the emitting defect core region is terminated by p:GaAs/air, and the other region terminates with p:GaAs/ Ti:Pt:Au.…”

“…First, with a 2-ring design [11], the fundamental mode exhibits lower radiation loss compared to the conventional ARROW, which helps to reduce the threshold gain requirement for the fundamental mode. By applying mirror absorption loss in the metal [8], we can further improve modal discrimination of these devices.…”