D. Vakhshoori

Top‐surface emitting lasers with 1.9 V threshold voltage and the effect of spatial hole burning on their transverse mode operation and efficiencies

The fabrication and operating characteristics of a 1.9 V top surface emitting laser are presented. A planar fabrication process with a modified ion implantation mask is used to achieve gain guided lasers operating up to 90 °C. The laser operates in the fundamental mode up to 0.7 mW with 3.2 mW total peak optical output power. Direct evidence of spatial hole burning for the fundamental and the next higher mode is observed. This spatial hole burning puts a limit on the fundamental mode operation and efficiency of the lasers.

Blue‐green surface‐emitting second‐harmonic generators on (111)B GaAs

Passive devices capable of generating coherent blue‐green light radiated in a surface emitting geometry is realized on (111)B GaAs substrates. This substrate orientation is required by the symmetry of the III–V crystals for the particular nonlinear counterpropagating interaction under consideration. The visible light output power versus the fundamental optical power is measured and shown to agree with the theory. This result demonstrates the feasibility of active visible surface emitting generators in the milliwatt output power range on (111)B substrate.

Strain compensated InGaAs-GaAsP-InGaP laser

The performance characteristics of InGaAs-GaAsP-InGaP strain compensated laser emitting near 1 /spl mu/m are reported. The ridge waveguide lasers have room temperature threshold current of 18 mA and differential quantum efficiency of 0.45 W/A/facet. The linewidth enhancement factor is smaller and gain coefficient is larger for these strain compensated lasers compared to that for conventional strained layer laser. This may be due to higher effective compressive strain in the light emitting layer of these devices which reduces the effective mass. The observed larger gain coefficient is consistent with the measured larger relaxation oscillation frequency of these lasers compared to that for a conventional strained layer laser.

8×18 top emitting independently addressable surface emitting laser arrays with uniform threshold current and low threshold voltage

Fabrication of 8×18 independently addressable vertical cavity surface emitting laser arrays (VC‐SELA) with uniform threshold current, threshold voltage, and high optical output power is reported. The top surface emitting array contains GaAs multiquantum well active regions and exhibits uniform characteristics over a 4×9 mm2 area. The cw threshold current is ≊4.2∓0.2 mA, the threshold voltage is 2.65∓0.1 V, and the output optical power is greater than 2 mW for the individual elements of the array. To realize these large VC‐SELAs, a novel ion implantation mask fabrication was developed.

Integrable semiconductor optical correlator, parametric spectrometer for communication systems

A broadband integrable waveguide correlator and parametric spectrometer is analyzed both theoretically and experimentally. The correlator can measure pulsewidths from subpicosecond to tens of picoseconds centered at wavelengths of 1.06 to 1.7 mu m without any mechanical alignment. The parametric waveguide spectrometer is shown to resolve not only the mode of a 1.3- mu m Fabry-Perot laser diode but also the shift of the modes as a function of bias current. The improvement of these integrable waveguide structures and their possible use in laser stabilization, the defining of fixed frequency channels, and other applications for coherent communication systems are also discussed. >

Analysis of visible surface‐emitting second‐harmonic generators

Analysis of blue/green/red coherent light radiated by surface‐emitting nonlinear generators is presented. It is shown that there are possibilities of obtaining efficient mW visible light out of these devices. Several problems in the calculation of the efficiency of these structures are discussed. These include the incorporation of the second‐harmonic reflections at the layer boundaries, the field and power continuity requirements, relation of device performances on different substrate orientations due to symmetry of the III‐V crystals, and an analysis of active surface‐emitting second‐harmonic generators.

Symmetry considerations in vertical‐cavity surface‐emitting lasers: Prediction of removal of polarization isotropicity on (001) substrates

The effects of crystalline and structural symmetry on the performance of vertical‐cavity surface‐emitting laser structures are studied by group theoretical techniques. It is shown that an asymmetrically designed active region (i.e., saw‐tooth quantum wells) will make the gain anisotropic with respect to the two different transverse polarization on (001) substrates with eigenvectors along [110] and [110] directions. Removal of gain degeneracies is also shown for tilted substrates with the corresponding tabulation of the eigendirections. The gain/loss anisotropicity is required to make polarization stablized lasers.

Experimental observation of vertical cavity with polarization birefringence using asymmetric superlattice

Vertical cavity etalons with asymmetric superlattice claddings have been fabricated. As predicted earlier, the cavities with sawtooth superlattice claddings grown on (100) oriented substrate are birefringent with the new optical axes along (011) and (011) directions. The difference in the resonant wavelengths of the cavity modes polarized along (011) and (011) are measured to be about +0.3 and −0.3 A for the two senses of our sawtooth superlattice structures. The change of the sign of the wavelength shift indicates that the observation is not due to an electro‐optic effect of the incorporated p‐n junction but is due to the reduction of the III‐V crystalline symmetry by the presence of the asymmetric superlattice.

BURIED HETEROSTRUCTURE LASER DIODES FABRICATED USING IN SITU PROCESSING

An in situ process which includes electron cyclotron resonance plasma etching and molecular beam epitaxial regrowth is applied to the fabrication of buried heterostructure vertical cavity surface‐emitting laser (SEL) diodes and edge‐emitting laser (EEL) diodes. The buried SEL with a 7.5 μm diameter has a pulsed laser threshold current of 1 mA, and a threshold voltage of 4 V with a peak power of 0.9 mW. The buried EEL with 2.5 μm stripe width and 800 μm cavity length has a threshold current density of 500 A/cm2.

Digital transmission link using surface emitting lasers and photoreceivers

Transmission system experiments using surface emitting lasers (SEL) and integrated photoreceivers have been carried out. The surface emitting laser utilizes proton implantation for current confinement and has a small signal bandwidth of 10 GHz. The p‐i‐n/modulation doped field effect transistor photoreceiver has a bandwidth of 11 GHz. Bit error rates of less than 10−9 were demonstrated using the SEL source and the photoreceiver. The receiver sensitivity is −16.5 dBm at 10 Gb/s.