We present an ultra-compact, hybrid faint pulse source (FPS) at 850 nm, making use of a linear eight VCSELs array at spectral (<1 pm wavelength difference, and >90% overlap at FWHM) and temporal (<1 ps) indistinguishability, as well as polarization quality in the four H/V/D/A BB84 channels >20 dB. A common VCSEL array on a single substrate is used, at a pitch of 250 μm and with integrated polarizers, having a spectral indistinguishability if the substrate is temperature levelled < 0.5 K. Each VCSEL represents either faint or full amplitude signal for the H/V/D/A channels of the BB84 protocol. The temperature levelling heatsink is made of Molybdenium, integrated on LTCC board to host the emitter substrate and its respective DAC driving circuit at speeds up to 10 GHz. VCSEL integrated micro-lenses and two additional micro-lens arrays fully collimate the beams and refocus them into a waveguide combiner chip which realizes the polarization independent coupling of all eight VCSEL free-space beams with a pulse delay variation <0.2 ps.
VCSELs emitting in the red spectral range are auspicious candidates for various applications, for example in biomedical utilization. However, their implementation is occasionally hampered especially due to the limited fiber coupling efficiency resulting from the beam divergence further increasing for higher power emission, where higher order transverse modes are emitted. Hence, the emission of a highly collimated Gaussian beam at raised output power is pursued in this work. The suppression of higher order modes through etched surface reliefs spatially modulating the reflectivity is investigated. To reduce the angle of divergence, polymer microlenses are integrated directly on the VCSEL surface.
In this contribution, we investigated the design of an AlGaAs/AlGaInP electrically-pumped VECSEL structure emitting at a wavelength of 665 nm. With the finite element method (FEM) of an electro-thermal numerical model, we analyzed the current density distribution in the active region of different laser structures by changing the structure geometry, doping concentration of current spreading layer, and bottom contact size. A complete flip-chip processing is proposed according to the optimized designed structure. The measured results of the electroluminescence (EL) profile indicate that the diameter of the emission area with quasi-Gaussian distribution can be up to 100 μm, which is in good agreement with the numerical simulation.
In this report, we investigated the optical gain properties and lasing characteristics of a laser structure consisting of one single-layer of self-assembled InP quantum dots in Al0.10GaInP barriers. The optical gain and absorption spectra are obtained by analyzing the amplified spontaneous emission. An internal optical loss value of 5±2 cm−1 , and a maximum peak modal gain of 39.3 cm−1 for a single-sheet of QD were obtained at room temperature. The influence of temperature on the gain properties was studied. A 2.24-mm-long laser with uncoated facets emitting at 660 nm was demonstrated. A low threshold current density of 281 A/cm2 with an external differential quantum efficiency of 34.2% was also achieved.
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