K. Panzlaff

Tunable extremely low threshold vertical-cavity laser diodes

Submilliampere-threshold wavelength-tunable three-terminal vertical-cavity laser diodes have been fabricated by proton implantation and wet chemical etching. Laser diodes of 8- mu m active diameter exhibit record low threshold currents of 650 mu A and emit upto 170- mu W output power under CW conditions and 0.4 mW under pulsed excitation. Slightly larger devices of about 12- mu m diameter emit up to 1.85 mW in a single mode under pulsed conditions. The emission wavelength is about 970 nm and matched to the spectral gain of the three active InGaAs quantum wells. Individual elements in a two-dimensional array can be continuously tuned over 2.2 nm by applying separate tuning currents of 70 mu A to the corresponding top mesa electrodes. Tuning and laser currents are controlled independently.<<ETX>>

Characterization of two-sided output vertical-cavity laser diodes by external optical feedback modulation

We have fabricated 5.6 nm wavelength tunable vertical-cavity laser diodes with record low CW threshold currents of 650 /spl mu/A. Laser output power depends on mirror reflectivities as well as intrinsic loss and effective internal efficiency which gives the conversion of carriers into photons of the lasing mode. To optimize laser mirror design for maximum output power it is important to know the loss and efficiency values. With in-plane lasers these intrinsic device parameters are commonly determined by measuring the threshold currents of equally processed devices of different cavity lengths. Obviously, this is impossible for vertical-cavity lasers even if in-plane lasers are made of epitaxial multilayers grown for vertical-cavity lasers due to different waveguiding mechanism. Therefore we have modulated the effective reflectivity of the vertical-cavity laser Bragg mirrors by external reflection to obtain the intrinsic parameters. We applied the technique for the first time to vertical-cavity laser diodes with two-sided light output but it can be applied to devices with one-sided output as well.<<ETX>>

Resonant wavelength selective photodetectors

The structure and fabrication of a wavelength selective photodetector is described. The experimentally achieved maximum quantum efficiency is more than 10% at resonance with 1.5nm spectral width at half maximum and a free spectral range of ca. 30nm. The optimum performance of resonant detectors is analyzed theoretically.

Vertical-cavity surface-emitting laser diodes for short distance optical fiber networks

We have fabricated wavelength tunable vertical-cavity laser diodes in 2D arrays by molecular beam epitaxy, proton implantation, and wet chemical etching. Record low threshold currents of 650 /spl mu/A for continuous wave and 600 /spl mu/A for pulsed operation are obtained for devices with 8 /spl mu/m active diameter. Output power is up to 170 /spl mu/W CW and 400 /spl mu/W pulsed. The emission is single longitudinal and transversal mode at about 970 nm wavelength. Three terminals for each laser diode supply two separate currents for the independent control of output power and emission wavelength of individual elements in a 2D laser array. A record wide continuous wavelength tuning range of 8.2 nm is achieved in a slightly larger device with tuning currents of just 2.5 mA. Highly efficient and alignment tolerant coupling to single-mode optical fibers is demonstrated with quasi-planar vertical-cavity laser diodes which provide a two-sided light output. Direct contact butt coupling to flat cut single-mode optical fibers of 4.5 /spl mu/m diameter core results in coupling efficiencies over 90%. The lateral alignment tolerances defined by a -3 dB coupling efficiency decrease are as large as 5.6 /spl mu/m. Maximum power coupled into a 9 /spl mu/m diameter core fiber is 0.75 mW for a non-heat sinked laser diode.<<ETX>>

TUNABLE VERTICAL-CAVITY LASER-DIODES WITH SUBMILLIAMP THRESHOLD CURRENTS AND EFFICIENT FIBER COUPLING

We have fabricated wavelength tunable vertical-cavity laser diodes on n-GaAs substrates in 2D arrays by molecular beam epitaxy, proton implantation, and wet chemical etching. Record low threshold currents of 650 (mu) A for continuous wave and 600 (mu) A for pulsed operation are obtained for 8 micrometers active diameter devices. Output power is up to 170 (mu) W cw and 400 (mu) W pulsed. The Bragg reflectors consist of AlAs-GaAs stacks. The active region contains three strained In0.2Ga0.8As quantum wells. The emission wavelength is about 960 nm. Three terminals for each laser diode supply two separate currents for independent control of output power and emission wavelength of individual elements in the 2D array. A record wide continuous wavelength tuning range of 5.6 nm is achieved with tuning currents just below 1 mA. Highly efficient and alignment tolerant coupling to single-mode optical fibers is demonstrated with modified vertical-cavity laser diodes. Quasi planar devices providing two-sided light output have been fabricated with an inverted npn-doping profile. Direct contact butt coupling to flat cut single-mode optical fibers of 4.5 micrometers diameter core results in over 90% coupling efficiency. The lateral alignment tolerances defined by a -3 dB coupling efficiency decrease are as large as 5.6 micrometers . Maximum power in 9 micrometers diameter core fibers is 0.75 mW for a non-heat-sinked device with 8 micrometers alignment tolerances. The easy fiber attachment is applicable to 2D laser arrays and mass production. The large alignment tolerances will improve reliability and drastically reduce packaging costs making vertical-cavity lasers very attractive for short distance optical interconnects.

Three-terminal vertical-cavity laser diodes for wavelength tuning and stabilization

In vertical-cavity laser-diode arrays the emission wavelength of individual devices varies across the array, mostly because of inhomogeneous growth conditions. Moreover, device heating by laser-diode current produces an undesired shift of the emission line. We present a three-terminal laser structure that uses current-induced extra heating of the top mirror mesa for efficient wavelength control. Unlike the devices described in Refs. 1 and 2, three electrodes are accessible from the top surface and the device is fully monolithic.

Modelocking of low threshold VCSEL with pigtailed fiber resonator

Summary form only given. We have generated 24 ps pulses using a modelocked vertical cavity surface emitting laser (VCSEL) with a fiber optic resonator. CW threshold current of the modelocking configuration is as low as 1.8 mA. The timing jitter of the pulses remains below 1 ps.

8.2 nm Continuous Wavelength Tuning of Three-Terminal Vertical-Cavity Laser Diodes

Vertical-cavity laser diodes are attractive light sources for short distance optical fiber networks due to low threshold currents and high coupling efficiency into single-mode optical fibers. We have fabricated vertical-cavity laser diode 2D arrays with independent wavelength tuning capability of each element exhibiting threshold currents as low as 650 pA [1].

Surface Emitting Laser Diodes and Wavelength Break Selective Photodetectors

The structure and fabrication of a vertical cavity surface emitting laser diode is described. The lowest threshold currents are 16mA. The light emission is single longitudinal mode at 915 nm wavelength. Under pulsed excitation the maximum output power is 3.5 mW. A wavelength selective photodetector of related structure shows a quantum efficiency of 10% at resonance with 1.5nm spectral width at half maximum.

Growth of InAlGaAs multilayer structures for high power and submilliamp vertical cavity lasers

Abstract We have used solid source molecular beam epitaxy (MBE) with As 4 to grow multilayer structures for vertical cavity surface emitting laser diodes (VCSEL) on n-GaAs substrates. Processed wafers with strained InGaAs active layers show a record low threshold current of 650 μA for 8 μm devices at an emission wavelength of 970 nm. In larger devices of 95 μm diameter we obtain 20 mW maximal cw output power applying proper heat sinking. Using strained InAlGaAs quantum wells with 25% In and 35% Al we observe a threshold current density of 1.1 kAcm −2 at an emission wavelength of 747 nm for broad area in-plane lasers.