Dependence of output coupling efficiency on detuning in surface grating output couplers

Abstract

The dependence of output coupling efficiency on the periodicity of a surface grating outcoupler was investigated. Horizontal cavity InGaAs/AlGaAs laser oscillators with two first-order surface gratings as feedback elements were integrated with detuned rectangular second-order gratings as surface output couplers by the use of electron-beam lithography and chemically assisted ion-beam etching. A high surface emission efficiency of more than 60% was achieved for grating periodicities detuned -2.5 nm to -15 nm and +2.5 nm from the resonance periodicity of 295 nm. For larger positive detuning, the surface emission efficiency is reduced because of the onset of secondorder diffraction into the substrate.

Finite aperture tapered unstable resonator lasers

“…Instead, light can be coupled from the forward to the out-coupled mode, and then to the backward propagating mode (Sec tion 3.4.4). Furthermore, this fleld can be commensurate with the field reflected from the low-reflectivity first-order grating, and is exacerbated if the first-order grating provides unstable cavity feedback, while the curved, second-order grating provides quasi-stable cavity feedback [38].…”

High efficiency surface emitting lasers using blazed grating outcouplers

“…7-12 For all the above, a laser oscillator separated from the outcoupler is required for optimal efficiency and flexibility. 4,6,11 In this work, we report on the best results from an extensive investigation of the SEE for various grating shapes and show that optimized blazed grating output couplers can provide overall laser efficiencies comparable to those of conventional edge emitters.…”

“…4 -12 An improvement of the surface emission efficiency ͑SEE͒, defined as the fraction of the light incident on the outcoupler that is radiated into the superstrate, can be achieved by optimizing the geometry of a rectangular grating and its detuning from the laser wavelength. 4 The SEE can be further enhanced by redirecting the beam radiated into the substrate using a Bragg reflector below the waveguide, carefully positioned in order to fulfill the phase matching condition. 5,6 Substantial improvement has also been suggested using asymmetric grating teeth, such as blazed gratings of sawtooth or paralellogramic shape.…”

“…1. The fabrication procedure was essentially equivalent to that in earlier work, 4,11,12 with the exception for the grating lithography. In this work we used ZEP 520 electron beam resist ͑from Nippon Zeon Co. Ltd.͒ which has a higher dose sensitivity, contrast, and resistance to ion beams than polymethylmethacrylate.…”

“…The 5 nm negative detuning suppresses unwanted feedback as well as second order diffraction into the substrate. 4 By varying the exposure linewidth, using a multiline exposure technique, seven different toothwidth-toperiod ratios ͑ϳ0.25-0.75͒ were obtained after etching. 13 This ratio will now be referred to as the grating duty cycle and denoted by d.…”