Enbo Xing

High-Power Ultralow Divergence Edge-Emitting Diode Laser With Circular Beam

A recognized drawback of edge-emitting diode lasers is their high divergence and elliptical beam shape since the first diode laser was demonstrated. In this paper, we demonstrated the ultranarrow circular beam emission from the broad area diode laser based on a modified Bragg-like waveguide. The low vertical divergence of 9.8° with 95% power content and 4.91° with the full-width at half-maximum was realized in the devices with 150 μm stripe width. The maximum output power was 4.2 W under quasi-continuous-wave operation and presently limited by thermal rollover. The detailed design principle was presented and it was found that reducing the refractive index and thickness of the defect layer was able to improve the vertical divergence and achieve the stable circular beam emission by controlling the lateral current distribution using the deep stripe. The packaged device with 90 μm stripe width demonstrated a maximum continuous wave power of 4.6 W at 10 °C. A direct fiber coupling efficiency of 90.6% had been achieved with a common fiber of 105 μm core diameter.

Tunneling control of cavity linewidth narrowing via quantum interference in triangular quantum dot molecules

A scheme for tunneling control of cavity linewidth narrowing by quantum interference in triangular-type triple quantum dots (TQDs) is proposed. In such system, quantum interference induced by tunneling between the TQDs can result in the appearance of two transparency windows and a steep dispersion. Furthermore, when the sample is embedded in a ring cavity, an ultranarrow transmission peak is obtained within the narrowed transparency windows. And by varying the tunneling, the linewidth and the position of the ultranarrow transmission peak can be engineered. Because no coupling laser is required, the scheme proposed here is more convenient for future experiments and applications in optics, and may be useful in designing novel optoelectronic devices.

Low lateral divergence 2 μm InGaSb/ AlGaAsSb broad-area quantum well lasers.

High power and high brightness mid-infrared GaSb based lasers are desired for many applications, however, the high lateral divergence is still the influence factor for practical application. In this paper, a simple and effective approach based on the fishbone-shape microstructure was proposed, the effective improvement on both the lateral divergence and output power of 2 μm GaSb based broad-area lasers was demonstrated. The lateral divergence is reduced averagely by 55% and 15.8° for 95% power content is realized. The continuous-wave emission power is increased about 19% with the decreased threshold current. The other merits for this microstructure are the unchanged intrinsic characteristic of broad-area lasers and the low cost fabrication.

Control of coherence transfer via tunneling in quadruple and multiple quantum dots

Transfer and manipulation of coherence among the ground state and indirect exciton states via tunneling in quadruple and multiple quantum dots is analyzed. By applying suitable amplitudes and sequences of the pump and tunneling pulses, a complete transfer of coherence or an arbitrary distribution of coherence of multiple states can be realized. The method, which is an adiabatic passage process, is different from previous works on quantum dot molecules in the way that the population can transfer from the ground state to the indirect exciton states without populating the direct exciton state, and thus no spontaneous emission occurs. This investigation can provide further insight to help the experimental development of coherence transfer in semiconductor structures, and may have potential applications in quantum information processing.

Control of lateral divergence in high-power, broad-area photonic crystal lasers

One-dimensional photonic bandgap crystal (PBC) lasers have demonstrated ultra-low vertical divergence and record brightness; however, their future development is limited by their lateral beam quality. In this paper, a fishbone microstructure is proposed to control the lateral modes in broad-area PBC lasers. The findings reveal that the introduction of the microstructure improves the full width at half maximum of the lateral far field by 22.2% and increases the output power to a small extent. The detailed measurements show that the lateral beam parameter product decreases by 15.9%.

High power 808 nm Bragg reflection waveguide lasers with ultralow beam divergence

Bragg reflection waveguide diode lasers emitting at 808 nm have demonstrated narrow near-circular shaped spot emission. The low vertical beam divergence of 8.3° and power of 1.75 W were achieved.