Yanfang Sun

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 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.

High-power vertical-cavity surface-emitting laser with an extra Au layer

We report the performance of a high-power vertical-cavity surface-emitting laser (VCSEL) with an extra Au layer. By using the extra Au layer, the far-field divergence angle from a 600-/spl mu/m diameter VCSEL device is suppressed from 30/spl deg/ to 15/spl deg/, and no strong sidelobe is observed in far-field pattern. There is a slight drop in optical output power due to the introduction of the extra Au layer. By improving the device packaging method, the VCSEL device produces the maximum continuous-wave optical output power of 1.95 W with lasing wavelength of 981.5 nm. The aging test is carried out under constant current mode at 60/spl deg/C, and the preliminary result shows that the total degradation of output power is less than 10% after 800 h.

Design and characterization of a nonuniform linear vertical-cavity surface-emitting laser array with a Gaussian far-field distribution

A 980 nm bottom-emitting vertical-cavity surface-emitting laser array with a nonuniform linear arrangement is reported to realize emission with a Gaussian far-field distribution. This array is composed of five symmetrically arranged elements of 200 microm, 150 microm, and 100 microm diameter, with center spacing of 300 microm and 250 microm, respectively. An output power of 880 mW with a high power density of 1 kW/cm2 is obtained. The divergence angle is below 20 degrees in the range of operating current from 0 A to 6 A. The theoretical simulation of the near-field and the far-field distribution is in good agreement with the experimental result. The comparison between this nonuniform linear array, the single device, and the conventional two-dimensional array is carried out to demonstrate the good performance of the linear array.

Vertical-external-cavity surface-emitting lasers operating at different wavelength: design, numerical simulation, and characteristics

We describe design, numerical simulation and characteristics of high-power optical pumped VECSELs at different wavelength (980nm, and 1300nm). The device design realizes the integrating diode-pumped lasers with vertical-cavity surface-emitting laser structure, drawing on the advantages of both. With periodical gain element structure, optical pumped VECSEL is scalable to watt level output. The characteristics such as threshold condition and output power are calculated theoretically. An optimum number of quantum wells and external mirror reflectivity are obtained from the calculation results, and the thermal characteristic is also considered. Finally the calculation results also predict high output power in this kind of device structure.

Self-pulsation in a two-section DFB laser with a varied ridge width

A 1.55 mu m InGaAsP-InP two-section DFB laser with a variable ridge width has been fabricated. Self-pulsations with frequencies around 3 GHz and 40 GHz are observed. The pulsation mechanisms related to the two frequencies are discussed and the tunability of generated self-pulsations is studied.

High Power VCSEL Device with Periodic Gain Active Region

High power vertical cavity surface emitting lasers with large aperture have been fabricated through improving passivation, lateral oxidation and heat dissipation techniques. Different from conventional three quantum well structure, a periodic gain active region with nine quantum wells was incorporated into the VCSEL structure, with which high efficiency and high power operation were expected. The nine quantum wells were divided into three groups with each of them located at the antinodes of the cavity to enhance the coupling between the optical field and the gain region. Large aperture and bottom-emitting configuration was used to improve the beam quality and the heat dissipation. A maximum output power of 1.4W was demonstrated at CW operation for a 400μm-diameter device. The lasing wavelength shifted to 995.5nm with a FWHM of 2nm at a current of 4.8A due to the internal heating and the absence of active water cooling. A ring-shape farfield pattern was induced by the non-homogeneous lateral current distribution in large diameter device. The light intensity at the center of the ring increased with increasing current. A symmetric round light spot at the center and single transverse mode operation with a divergence angle of 16° were observed with current beyond 4.8A.

EFFECTS OF EXTERNAL OPTICAL FEEDBACK ON THE OSCILLATING CHARACTERISTICS OF 980nm VERTICAL-CAVITY SURFACE-EMITTING LASERS: EFFECTS OF EXTERNAL OPTICAL FEEDBACK ON THE OSCILLATING CHARACTERISTICS OF 980nm VERTICAL-CAVITY SURFACE-EMITTING LASERS

The effects of external optical feedback (OFB) on the oscillating characteristics of 980nm vertical-cavity surface-emitting lasers (VCSEL) were investigated. The OFB sensibility of VCSEL and edge emitting lasers ( EEL) were evaluated by calculating OFB parameters. Based on the compound cavity theory, the effects of external optical feedback on the oscillating characteristic parameters of VCSEL, such as the threshold current and the differential quantum efficiency, were analyzed. The experimental results indicate that the threshold current of the VCSEL decreases from 0.63A to 0.59A when the feedback ratio is 10%. Meantime, the slope efficiency and the output power also decrease. The result of experiment is in good agreement with the calculation.

Large aperture low threshold current 980nm VCSELs fabricated with pulsed anodic oxidation

Pulsed anodic oxidation technique, a new way of forming current blocking layers, was successfully used in ridge-waveguide QW laser fabrication. We apply this method in 980nm VCSELs fabrication to form a high-quality native oxide current blocking layer, which simplify the device process. A significant reduction of threshold current and a distinguished device performance are achieved. The 500μm-diameter device has a current threshold as low as 0.48W. The maximum CW operation output power at room temperature is 1.48W. The lateral divergence angle θparalleland vertical divergence angle θperpendicular are as low as 15.3° and 13.8° without side-lobes at a current of 6A.

High-power VCSELs single devices and 2-D arrays

The high power bottom-emitting vertical-cavity surface-emitting lasers (VCSELs) and laser arrays emitting at 980 nm are reported. Extensive investigations on size scaling behavior of thermal properties of single devices show limits of attainable output characteristics. The maximum continuous wave (CW) output power at room temperature of single devices with aperture size up to 500 μm is as high as 1.95 W. The key characteristics such as maximum output power, wavelength and thermal resistance are discussed. The bottom-emitting arrays of 16 elements and 200 μm aperture size of individual elements show output power of CW 1.35 W at room temperature. The far-field angle is below 17° for all driving current, which is very favorable for focusing or collimating optics.