Low threshold current density operation of GaInP-AlGaInP visiblemultiple quantum wire-like lasers (MQWR-LDs) under the room temperaturepulsed condition

GaInP-AlGaInP multiple quantum wire-like layers were fabricated by the in situ strain induced lateral layer ordering process during MBE growth. According to TEM images, the quantum wire size was around 10 nm and quantum wire axis was along [011¯] direction. When we made laser diodes with stripes along [011] direction, the low threshold current density, of 315 A/cm² was obtained. Anisotropic lasing characteristics between [011] and [011¯] directions, in threshold current density, lasing mode, and lasing wavelength were observed     

Polarization characteristics of 850-nm vertical-cavity surface-emitting lasers with intracavity contacts and a rhomboidal oxide current aperture

The polarization characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts and a rhomboidal oxide current aperture are studied. It is found that radiation polarization is always directed along the minor diagonal of the rhomboidal aperture (along the [\(\overline 1 \) 10] direction) for all single-mode VCSELs. The numerical simulation of carrier transport does not reveal the significant anisotropy of carrier injection to the active region. Furthermore, an analysis of the spatial distribution of the fundamental mode for two orthogonal polarizations within an effective waveguide model shows close transverse optical-confinement factors. Optical loss anisotropy in the asymmetric microcavity and/or gain anisotropy in the strained active region are the most likely mechanisms responsible for fixing the polarization.     

Spin controlled optically pumped vertical cavity surface emitting laser

It is shown that the output polarisation of optically pumped vertical cavity surface emitting lasers (VCSELs) can be unambiguously controlled by the pump polarisation. The degree of the output polarisation is higher than that of the pump polarisation. It is concluded that the polarisation of VCSELs with spin polarised electrical pumping can be controlled even with low spin injection efficiencies.     

High-power fundamental-mode and polarisation stabilised VCSELs using sub-wavelength surface grating

A monolithic technique is presented for simultaneous mode and polarisation control in oxide-confined VCSELs using a locally etched sub-wavelength surface grating. A single-fundamental-mode emission with an SMSR >30 dB and an OPSR /spl sim/20 dB is achieved over the entire operational current range, with a maximum output power of 4.1 mW.     

Optical characteristics of multitransverse-mode two-dimensionalvertical-cavity top surface-emitting laser arrays

We observe for the first time up to nine transverse modes lasing in the individual elements of a two-dimensional vertical-cavity top surface-emitting laser array under pulsed operation. These modes consist of the TEM_0,0, TEM_0,1, TEM_1,0, TEM_1,1, TEM_0,2, TEM_2,0, TEM_1,2 , TEM_2,1, and TEM_2,2 modes, Each of these modes couples coherently across the array to form very distinct supermodes. The transverse modes as well as the resulting supermodes are identified by examining the near-field and far-field profiles as well as the corresponding spectra. We also obtain a record 1.4 W (pulsed) of coherent output power from the array during multitransverse-mode operation. In addition, the polarization properties of the array are investigated, It is found that the TEM_0,1 mode is horizontally polarized along the [011] crystalline axis while all the other modes are dominantly vertically polarized along the [011¯] axis     

Single-mode power dependence on surface relief size formode-stabilized oxide-confined vertical-cavity surface-emitting lasers

We have studied the mode behavior of oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with a surface relief for fundamental mode selection. The dependence of single-mode power on the surface relief diameter was measured and compared with numerically calculated values. VCSELs with diameters of 9 and 12 μm were equipped with surface reliefs with diameters in the range 4-10 μm. The results show that there exists an optimum relief diameter for each VCSEL size. A maximum single-mode power of 2.2 mW was achieved for a 9-μm-diameter VCSEL with a 4-μm-diameter surface relief     

Single fundamental mode photonic crystal vertical cavity laser with improved output power

The single fundamental mode output power of photonic crystal vertical cavity lasers is improved by varying sizes of oxide apertures and defect lasing apertures. A maximum output power of 3.1 mW in the fundamental mode has been achieved with a new fabrication process that involves only focused ion beam etching to create holes in selectively oxidised VCSELs.     

High performance selectively oxidized VCSELs and arrays forparallel high-speed optical interconnects

High-bandwidth single-mode selectively oxidized vertical-cavity surface-emitting laser (VCSEL) arrays operate at 980 nm or 850 nm emission wavelength for substrate or epitaxial side emission. Coplanar feeding lines and polyimide passivation are used to reduce electrical parasitics in top-emitting GaAs and bottom-emitting InGaAs VCSELs. To enhance fundamental single-mode emission for larger devices of reduced series resistance a surface relief transverse mode filter is employed. Fabricated VCSELs are applied in various interconnect schemes. InGaAs quantum-well based VCSELs at 935 nm emission wavelength are investigated for use in perfluorinated graded-index plastic-optical fiber (GI-POF) links. We obtain a 7 Gb/s pseudo random bit sequence (PRBS) nonreturn-to-zero (NRZ) data transmission over 80 m long 155 μm diameter GI-POF. We investigate data transmission over standard 1300 nm, 9 μm core diameter single-mode fiber with selectively oxidized single-mode GaAs and InGaAs VCSELs. We achieve biased 3 Gb/s and bias-free 1 Gb/s pseudo-random data transmission over 4.3 km at 830 nm emission wavelength where a simple fiber mode filter is used to suppress intermodal dispersion caused by the second order fiber mode. For the first time, we demonstrate 12.5 Gb/s data rate transmission of PRBS signals over 100 m graded-index multimode fiber or 1 km single-mode fiber using high performance single-mode GaAs VCSELs of 12.3 GHz modulation bandwidth emitting at λ=850 nm     

Fabrication of polarisation-maintaining [3×3] single-mode-fibre couplers

[3×3] fused fibre couplers have been fabricated with polarisation-maintaining and absorption-reducing (PANDA) fibres. The couplers can hold linear polarisation along the principal axis of the fibre branches, showing an extinction ratio better than ?15 dB.     

1.3-μm GaInAsN Vertical-Cavity Surface-Emitting Lasers by Oxide-Planarized and Surface-Relief Processes for Single-Mode Operation

In this letter, we investigate and characterize the 1.3-mum single-mode vertical-cavity surface-emitting lasers (VCSELs) with two GaInAsN strained multiple quantum wells as the active region. Surface relief technique and a thick silicon oxide were used for the spatial mode filtering and the planarization processing, respectively. The VCSELs with a 5-mum-diameter surface-relief aperture and a 12-mum-diameter oxide-confined aperture at room temperature exhibit a threshold current of 3 mA, a slope efficiency of 0.14 mW/mA, a maximum operation temperature of 90 degC, and a single-mode behavior. These VCSELs show a maximum light output power of 1 mW for the single fundamental mode with a transverse-mode suppression of more than 30 dB and also show a clear eye-opening feature operated at 2.488 Gb/s and 12.6 mA     

Enhancement of spin information with vertical cavity surface emitting lasers

How the output polarisation of vertical cavity surface emitting lasers (VCSELs) can be controlled by the spin polarisation of the electrons in the active region is analysed. The main result is that a spin controlled VCSEL is feasible under realistic device conditions, i.e. at room temperature and for continuous wave operation.     

Optical anisotropy of InGaAs quantum dots

Polarization studies of InGaAs/GaAs quantum dots (QDs) synthesized in the submonolayer deposition mode (SMLQDs) on a singular GaAs (100) surface are carried out using photoluminescence spectroscopy. The influence of the effective In content in InGaAs SMLQDs and the effect of a wide-gap AlGaAs matrix on the optical anisotropy of the QDs are investigated. The highest degree (>15%) of optical anisotropy between the [011] and [0 $ \bar 1 $ 1] directions in the emission corresponding to the ground state of InGaAs/GaAs SMLQDs is observed for an effective In content of ～40%. The use of a wide-gap AlGaAs matrix resulted in an increase in the optical anisotropy of InGaAs SMLQDs by a factor of 1.5. It is found that vertical stacking of In(Ga)As/AlGaAs SMLQDs in the vertical-coupling mode (with spacer-layer thicknesses of 5–10 nm) leads to a further increase in the degree of optical anisotropy, which becomes as high as 25% on average. According to the data of transmission electron microscopy, the optical anisotropy of the ground-state photo-luminescence is predominantly caused by the anisotropy of the lateral dimensions of QDs in the [011] and [0 $ \bar 1 $ 1] directions.     

Characterization of cross-hatch morphology of MBE (211) HgCdTe

We present the results of a detailed study of the nature and origin of cross-hatch patterns commonly observed on (211) HgCdTe epilayers deposited by molecular beam epitaxy. Cross-hatch patterns were examined using x-ray topography as well as Nomarski, interferometric, and atomic force microscopies. Cross-hatch patterns were generally comprised of three sets of lines, parallel to the [231],, [213], and [011] directions. The lines parallel to the [011] direction exhibited distinct properties compared to the two sets of lines parallel to [231] and [213]. Under growth conditions characterized by excessive Hg flux (low temperature), lines parallel to [011] were periodic and tended to dominate the cross-hatch pattern. In some cases, bands of dislocations, 10–100 m in width, formed parallel to [011]. Under optimized growth conditions, on very closely lattice-matched substrates, (dislocation densities <10⁵ cm⁻²) lines parallel to [011] vanished entirely, and lines parallel to [231] and [213] became sparse. The remaining lines were typically fragments terminated by either a single dislocation, a cluster of dislocations (micro-void), or the wafer's edge. The density of these line fragments tended to decrease as the dislocation density decreased. Under the best growth conditions on very closely lattice-matched substrates we have achieved dislocation densities of 5 10⁴ cm⁻², which is comparable to the dislocation density of the CdZnTe substrate.     

Dynamic behavior of fundamental-mode stabilized VCSELs using a shallow surface relief

An extensive theoretical study was performed on the dynamic behavior of 850-nm-wavelength oxide-confined fundamental-mode stabilized vertical-cavity surface-emitting lasers (VCSELs), using a shallow surface relief. The surface relief is used to provide lower mirror loss for the fundamental mode, thus acting as a mode discriminator. In this way, single-mode operation at high power levels can be obtained. We utilized a comprehensive model that includes the detailed epitaxial layer structure and device geometry when calculating the optical fields and that accurately accounts for the dynamic effects of carrier density and temperature on the modal distributions. Modulation response, eye diagrams, bit error rate (BER), and relative intensity noise (RIN) were simulated and compared to the performance of VCSELs without a mode discriminator, i.e., conventional multimode VCSELs. The fundamental-mode stabilized VCSELs are associated with a higher out-coupling, which lowers the relaxation oscillation frequency and damping, and strong spatial hole burning, which induces a low-frequency roll-off in the modulation response and contributes to the damping of the relaxation oscillation at low bias. However, their dynamics is fully competitive with conventional multimode VCSELs at both 2.5 and 10 Gb/s although they exhibit a slightly higher eye closure. We only found a 0.5-dB power penalty in the BER. The RIN is enhanced, with a peak that is about 10-15 dB higher, caused by the lower damping of the relaxation oscillation. It should be noted that in the comparison we assume that all modes are equally captured from the multimode VCSEL. A mode-selective loss can severely degrade its performance.     

Influence of interface growth steps on the anisotropy of excitonic emission in ZnCdSe/ZnSe quantum wells

Spectra of excitonic luminescence of single-quantum-well ZnCdSe/ZnSe heterostructures at T = 8 K are investigated. Two types of linear-polarization anisotropy of the excitonic emission are revealed. The first type of anisotropy corresponds to the luminescence polarization along the [011] axis and is related to the emission from the lower level of the doublet state of heavy-hole excitons localized in the islands elongated in the $[0\overline 1 1]$ direction. The second type of anisotropy is related to the generation of free excitons with wave vectors exceeding that of light. Such a process is made possible by the elastic scattering of light at anisotropic interface-roughness structure originating from the growth steps. In this case, the emission is polarized along the [0-11] axis and the anisotropy is caused by deformation effects that lead to the perturbation of the hole states in the vicinity of the growth steps. The deformation appears due to a mismatch between the lattice constants of the barrier and the well materials.     

A low-threshold polarization-controlled vertical-cavitysurface-emitting laser grown on GaAs (311)B substrate

We have demonstrated a GaAs (311)B vertical-cavity surface-emitting laser (VCSEL) with a threshold current as low as 250 μA, which is the lowest value ever reported for that on non-(100) oriented substrates. Also, the fabricated VCSEL shows a stable polarization state for wide during current ranges and a large polarization-mode suppression ratio over 30 dB between the [2¯33] and [011¯] axis modes at 5 mA. The electrical specific resistance of 1.2×10^-4 Ω·cm^-2 at the threshold was reasonably low due to carbon autodoping to AlAs in a p-type distributed Bragg reflector (DBR)     

Large- and small-signal modulation properties of red (670 nm) VCSELs

The large- and small-signal properties of red GaInP-AlGaInP triple QW VCSELs (670 nm) were measured. For the fundamental mode the small signal bandwidth is 2 GHz. Large-signal modulation up to 1.5 Gb/s is achievable with a prebias. The turn-on delay of unbiased devices is found to saturate due to heating from the average of the data signal.     

"Anti" up the aperture [antiguided VCSEL structures]

Coupled vertical cavity surface-emitting laser (VCSEL) arrays are an attractive means to increase the coherent output power of VCSELs. Single-mode VCSELs, with output powers greater than 10 mW, would be useful as telecommunication transmitters /spl lambda/=1.3-1.55 /spl mu/m) or sources for optical interconnects. Commercially available single-mode VCSELs, even at shorter wavelengths /spl lambda/=0.85 /spl mu/m), are generally limited to a few milliwatts of output power. The conventional VCSEL structure incorporates a built-in positive-index waveguide, designed to support a single fundamental mode. Promising results in the 3-5 mW range (/spl lambda/=0.85 /spl mu/m) have been obtained from wet-oxidized, positive-index-guided VCSELs with small emission apertures (less than 3.5 /spl mu/m-dia). The small aperture size leads to a high electrical resistance and high current density, which can impact device reliability. By contrast, antiguided VCSEL structures have shown promise for achieving larger aperture single-mode operation. To obtain high single-mode powers with a larger emitting aperture, the use of a negative-index guide (antiguide) is beneficial. This paper discusses antiguided structures and some of their advantages when incorporated in 2-D VCSEL array structures.     

Computer simulation of an operation of the GaInP/AlGaInP QW VCSELs: Excitation of various transverse LPij modes

A comprehensive fully self-consistent optical–electrical–thermal-recombination model of the 650-nm oxide-confined GaAs-based GaInP/AlGaInP vertical-cavity surface-emitting diode lasers (VCSELs) is used to determine their anticipated room-temperature (RT) continuous-wave (CW) performance characteristics. As expected, for the devices with very large active regions, higher-order transverse LP_ij modes exhibit the lowest lasing thresholds. However, the desired single fundamental LP₀₁ mode operation remains dominating one for relatively large active regions of diameters up to as much as 10 mm. Therefore, the 650-nm GaInP/AlGaInP QW VCSELs have been found to offer a very promising RT CW performance as sources of carrier radiation for the optical communication taking advantage of plastic (polymer) optical fibers (POFs).     

High-performance GaAs MESFETs fabricated on misoriented (100) InPsubstrates by heteroepitaxy

MBE (molecular-beam-epitaxially)-grown GaAs MESFETs with 1.3 μm gate length were fabricated on a (100) InP substrate 3° misoriented towards [011] axis. The transconductance is between 120 and 170 mS/mm. These values are claimed to be the highest ever reported on this material. Device microwave characteristics are reported. An average cutoff frequency of 11 GHz is close to the 13 GHz cutoff frequency of similar devices made on GaAs substrates. It is agreed that the excellent DC and microwave performances are mainly due to the use of misoriented InP substrates and special MBE growth procedures