Yongqiang Ning

Controlling optical bistability via interacting double dark resonances in linear quantum dot molecules

The behavior of optical bistability (OB) in linear triple quantum dot molecules (QDMs) using double tunneling coupling by means of a unidirectional ring cavity is investigated. The linear and nonlinear susceptibilities of the system are also investigated. The double tunneling between the quantum dots can induce the interaction of double dark resonances, which can enhance the nonlinear response of the system. The type, the hysteresis loop, and the threshold of OB can be controlled by the intensity of the double tunneling and the detuning of the probe field. Our results give insights for future experiments and applications in optics using QDMs

Giant Kerr nonlinearity induced by tunneling in triple quantum dot molecules

A scheme for giant enhancement of the Kerr nonlinearity in linear triple quantum dot molecules is proposed. In such a system, the tunneling-induced transparency window obtained in double quantum dot molecules splits into two windows, due to the coupling with the third quantum dot. And most important, the Kerr nonlinearity can be enhanced by several orders of magnitude, compared with that generated in double quantum dot molecules. With proper detuning of the tunneling, giant Kerr nonlinearity accompanied by vanishing absorption can be realized, which opens the possibility to enhance self-phase modulation in tunneling controllable semiconductor nanostructures under conditions of low light levels. Quantitative analysis shows that the giant Kerr nonlinearity is attributed to the interacting double dark resonances induced by the tunneling between the triple quantum dots, therefore no extra laser fields are required.

A high power InGaAs/GaAsP vertical-cavity surface-emitting laser and its temperature characteristics

A high power bottom-emitting InGaAs/GaAsP vertical-cavity surface-emitting laser with a large aperture (400 µm diameter) is described. The device has been fabricated by using oxidation confinement technology. The device threshold current is 610 mA, and the maximum output power is up to the watt regime (1.42 W) at room temperature (24 °C) with a pulse condition (pulse width of 50 µs, repetition rate of 1 kHz). The maximum continuous wave optical output power at room temperature is as high as 1.09 W. The lasing peak wavelength is 987 nm, the full width at half-maximum is 0.9 nm, and the far-field divergence angle is below 10°. The temperature characteristics of the device are also obtained. A special temperature dependence of the threshold current in the vertical-cavity surface-emitting laser structure is observed; the characteristic temperature T0 is over 220 K, and the wavelength shift with temperature is only about 0.06 nm K−1.

High power and good beam quality of two-dimensional VCSEL array with integrated GaAs microlens array.

High power and good beam quality of two-dimensional bottom-emitting vertical-cavity surface-emitting laser array with GaAs microlens on the substrate is achieved. Uniform and matched convex microlens is directly fabricated by one-step diffusion-limited wet-etching techniques on the emitting windows. The maximum output power is above 1 W at continuous-wave operation at room temperature, and the far-field beam divergence is below 6.6° at a current of 4 A. These properties between microlens-integrated and conventional device at different operating current are demonstrated.

High-power vertical-cavity surface-emitting laser with an optimized p-contact diameter

A 980 nm bottom-emitting vertical-cavity surface-emitting laser (VCSEL) with a p-contact diameter is reported to achieve high power and good beam quality. A numerical simulation is conducted on the current spreading in a VCSEL with oxidation between the active region and the p-type distributed Bragg reflector. It is found that, for a particular oxide aperture diameter, somewhat homogeneous current distribution can be achieved for a VCSEL with an optimized p-contact diameter. The far-field divergence angle from a 600 microm diameter VCSEL is suppressed from 30 degrees to 15 degrees, and no strong sidelobe is observed in the far-field pattern by using the optimized p-contact diameter. There is a slight rise in threshold and optical output power that is due to the p-contact optimization. By improving the device packaging method, the maximum optical output power of the device is 2.01 W.

Design and comparison of GaAs, GaAsP and InGaAlAs quantum-well active regions for 808-nm VCSELs

Vertical-cavity surface-emitting lasers emitting at 808 nm with unstrained GaAs/Al0.3Ga0.7As, tensilely strained GaAs(x)P(1-x)/Al0.3Ga0.7As and compressively strained In(1-x-y)Ga(x)Al(y)As/Al0.3Ga0.7As quantum-well active regions have been investigated. A comprehensive model is presented to determine the composition and width of these quantum wells. The numerical simulation shows that the gain peak wavelength is near 800 nm at room temperature for GaAs well with width of 4 nm, GaAs0.87P0.13 well with width of 13 nm and In0.14Ga0.74Al0.12As well with width of 6 nm. Furthermore, the output characteristics of the three designed quantum-well VCSELs are studied and compared. The results indicate that In0.14Ga0.74Al0.12As is the most appropriate candidate for the quantum well of 808-nm VCSELs.

High-Power Large-Aperture Bottom-Emitting 980-nm VCSELs With Integrated GaAs Microlens

Microlens-integrated bottom-emitting 980-nm vertical-cavity surface-emitting lasers (VCSELs) with an emitting window aperture of 400 mum have been fabricated. A novel material structure with nine InGaAs-GaAsP quantum wells and slightly decreased reflectivity of n-type distributed Bragg reflectors (n-DBRs) are employed to increase the output power. A convex microlens is fabricated by a one-step diffusion-limited wet-etching technique on the GaAs substrate. The diameter of the active layer is about 200 mum after lateral oxidation, and the nominal diameter of the microlens is 400 mum. The maximum output power is 200 mW at continuous-wave operation at room temperature. The far-field divergence angles thetas|| and thetasperp of the single device at a current of 4A are 8.7deg and 8.4deg, respectively. The optical beam performance between the microlens-integrated VCSEL and ordinary VCSEL is compared.

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.

Graphene induced high-Q hybridized plasmonic whispering gallery mode microcavities

A novel hybridized plasmonic whispering gallery mode (WGM) microcavities composed of graphene monolayer coated ZnO microrod with hexagonal cross section were proposed that operates in the ultraviolet region. π and π + σ surface plasmon modes in graphene monolayer at 4.7 eV and 14.6 eV can be used to achieve the near field coupling interaction between surface plasmonic modes and the conventional WGM microcavity modes in the ultraviolet band. Significantly, the coupling, happened in the evanescent wave field excited along the interface between ZnO and graphene, can lead to distinct optical field confinement and lasing enhancement experimentally, so as well as WGM lasing characteristics, such as the higher cavity quality factor (Q), narrower linewidth, lasing intensities enhancement. The results could provide a platform to study hybridized plasmonic cavity dynamics, and also provides the building blocks to construct graphene based novel microcavity for high performance ultraviolet laser devices with potential application to optical signal processing, biological monitoring, and so on.

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.