Polarization-insensitive InP-based MQW digital optical switch

A polarization-insensitive InP-based p-i-n multiple-quantum-well switch is demonstrated for the first time. Polarization-insensitive switching and loss are achieved. Crosstalk and loss measurements across a wavelength range of 20 nm centered at 1.55 μm are reported. A crosstalk of better than -13 dB is achieved for both TE and TM polarizations across the 1.54-1.56-μm wavelength range with a switching voltage of -7 V. A low on-chip loss of less than 3 dB is achieved for both TE and TM across the above wavelength range, with a compact switch structure which is 3 mm long     

Optical waveguides in SIMOX structures

Propagation characteristics determined experimentally and theoretically for planar optical waveguides formed in separation by implantation of oxygen (SIMOX) structures are discussed. All samples were found to support both TE and TM modes at both 1.15 μm and 1.523 μm with a lowest propagation loss of 8 dB/cm. This loss was measured at a wavelength of 1.15 μm for the TE₀ mode of a planar waveguide with a 2.0-μm-thick Si guiding layer     

Polarization-independent waveguide modulators using 1.57-μmδ-strained InGaAs-InGaAsP quantum wells

We fabricated a multiple-quantum-well waveguide modulator incorporating two tensile S-strained layers, within a nominally lattice matched well, that act to provide bias-independent Stark shift for both the light and heavy holes. We report results for two waveguide geometries. One is a 2.3-μm-wide ridge single-mode waveguide that was deep-etched 0.7 μm below the active region to ensure that the confinement factor for both the TE and TM modes are nearly equal. The other was a broad-area (slab) multimode waveguide. For both geometries, transmission measurements indicate polarization insensitivity within 3 dB for 2.5 V of reverse bias over the 1.600-1.630-μm wavelength range     

Fabrication of tapered couplers in GaAs/GaAlAs rib waveguides

Tapered couplers have been fabricated in GaAs/GaAlAs single-mode rib waveguides. A new etching technique has been used to fabricate transitions of 1 μm over lengths of approximately 160 to 300 μm. Losses for the TE and TM fundamental modes have been measured at a wavelength of 1.3 μm     

High-power operation in 0.98-μm strained-layer InGaAs-GaAssingle-quantum-well ridge waveguide lasers

High power strained-layer InGaAs-GaAs graded-index separate confinement heterostructure (GRIN-SCH) single-quantum-well (SQW) lasers at an emission wavelength of 0.98 μm have been fabricated. A light power as high as 270 mW and a maximum front power conversion efficiency of 51.5% have been obtained for the antireflective and highly-reflective coated laser with 9-μm-wide ridge and 600-μm-long cavity     

Polarization-insensitive optical amplifier withtensile-strained-barrier MQW structure

A new approach to achieving a polarization-insensitive semiconductor optical amplifier is presented. The active layer consists of a tensile-strained-barrier MQW structure that enhances TM mode gain. Polarization sensitivity below 0.5 dB is realized at a wavelength of 1.56 μm. A signal gain of 27.5 dB is obtained along with a saturation output power of 14 dBm. Deriving the refractive indices of well and barrier layers from both experiment and theory, we succeed in separation of the effect of the confinement factor and the gain coefficient. It is determined that TM mode gain enhancement in this structure is primarily due to the increase in the confinement factor     

1.3-μm polarization-insensitive optical amplifier structurebased on coupled quantum wells

We show that polarization-insensitive optical gain over a wide bandwidth can be realized in a coupled pseudomorphic multiple-quantum-well structure. The barrier width is chosen such that heavy-hole subbands are grouped tightly and light-hole subbands are widely separated in energy. For specific strain conditions, the uppermost valence subbands, which have large occupation probability and strongly contribute to the gain, consist of a single light-hole subband and a group of coupled heavy-hole subbands. This arrangement gives rise to balanced gains for the TE and TM polarizations. We present calculated results for 1.3-μm semiconductor optical amplifier structures based on bands calculated in the framework of an eight-band k·p model. Two different material systems are examined, InAlGaAs and GaInAsP, on InP substrates     

Propagation loss measurements in semiconductor microcavity ring anddisk resonators

We report the measurement of cavity propagation losses in nearly single-mode semiconductor waveguide-coupled ring and disk microcavity optical resonators. Using a novel 10.5-μm-diameter ring resonator, we measure transverse electric (TE) and transverse magnetic (TM) field intensity losses in 0.35-μm-wide ring waveguide cavities in the 1.55-μm-wavelength region. We present the experimental results for nanofabricated AlGaAs-GaAs 10.5-μm-diameter ring and disk resonators to quantify cavity losses and to show the feasibility of these promising and robust submicron-scale devices     

2×2 optical waveguide switch with bow-tie electrode based oncarrier-injection total internal reflection in SiGe alloy

Based on the total internal reflection and the plasma dispersion effect of SiGe alloy, a 2×2 intersectional rib optical waveguide switch with bow-tie electrode has been proposed and fabricated for the wavelength of 1.3-μm operation. The thickness of the SiGe layer is 2.6 μm and the width is 9 μm. The branch angle of the switch is 2° and the bow-tie angle is 1.5°. The on-state crosstalk is -19.6 dB, the off-state extinction ratio is 38.5 dB and the off-state insertion loss is less than 1.70 dB. The switching time is about 180 ns     

A new cobalt salicide technology for 0.15-μm CMOS devices

A new cobalt (Co) salicide technology for sub-quarter micron CMOS transistors has been developed using high-temperature sputtering and in situ vacuum annealing. Sheet resistance of 11 Ω/□ for both gate electrode and diffusion layer was obtained with 5-nm-thick Co film. No line width dependence of sheet resistance was observed down to 0.15-μm-wide gate electrode and 0.33-μm-wide diffusion layer. The high temperature sputtering process led to the growth of epitaxial CoSi ₂ layers with high thermal stability. By using this technology 0.15 μm CMOS devices which have shallow junctions were successfully fabricated     

Scalability study of laser-induced vertical make-link structure

The scalability of a direct metal-to-metal connection between two different levels of metallizations has been extrapolated to be compatible with modern semiconductor fabrication technology. A simple equation to evaluate the scalability was formulated based on focused ion beam (FIR) cross-sectional images of larger link structures with various sizes. With a 0.6-μm-thick metal 1 line and a 0.5-μm-thick interlevel dielectric (ILD), a width of less than 0.5 μm is evaluated to be possible for the metal 1 line. Two limitations exist in the process of scaled-down link structures, which are the ratio of the thickness of ILD to the thickness of the metal 1 line, t_ILD/t _m, and the quality of laser beam parameters including the spot size and positioning error. However, modern processing technologies and advanced laser processing systems are considered to allow the scalability of a vertical make-link structure. Two layouts of two-level interconnects were designed with increased interconnect densities with a 1-μm pitch of a 0.5-μm-wide metal 1 line. These results demonstrate the application of commercially viable vertical linking technology to very large-scale integration (VLSI) applications     

Elusive bit-error-rate floors resulting from transient partitioningin 1.5-μm DFB lasers

Some 1.5-μm distributed feedback (DFB) lasers modulated at 1.7 Gb/s exhibit bit-error rate (BER) floors for certain fiber lengths, and hence these floors are difficult to detect. For example, a laser that does not exhibit a BER floor for 43 km of fiber may exhibit a BER floor after only 27 km. It is shown that the source of such BER floors is a narrow pulse resulting from transient partitioning between the DFB TE and TM modes. The narrow TM pulses cause false bits if the fiber delay between the modes positions the TM energy within a zero time slot. It is shown that for the 11 lasers studied, TM partitioning floors rarely occur in lasers with adequate threshold gain difference. When the duration of the TM partitioning is only a small fraction of a bit period, the BER floor is effectively removed using a polarized film in the transmission path to suppress the TM mode. Similarly, increased suppression of the TM mode has been achieved by changing the laser structure to reduce the TM mode gain     

Integration of magnetooptical waveguides onto a III-V semiconductorsurface

Optical waveguides fabricated on a yttrium iron garnet (YIG) substrate are integrated onto a semiconductor surface by using ridge waveguides patterned onto a prefabricated recess in the YIG surface. The recess separates the waveguides from the semiconductor substrate with an air-gap. This structure makes it possible to avoid coupling light within the YIG waveguides into the semiconductor substrate which has a higher refractive index. The excess optical loss due to the coupling can be as low as ⩽0.1 dB/cm with a 1-μm-wide air-gap. The calculated coupling loss is confirmed by comparing the guided TE and TM modes     

Focusing characteristics of a wide-striped laser diode integratedwith a microlens

We developed a wide-striped laser diode integrated with a microlens that provides good focusing characteristics through a small focusing spot. We calculated and demonstrated that a 60-μm-wide core and a 1.9-μm-high ridge is the best structure for fundamental index-guiding mode oscillation of a wide-striped laser diode. We integrated a wide-striped laser diode with the developed microlens in the Fresnel diffraction held, and demonstrated that a device with a 60-μm-wide core has a minimum focusing spot width of 2.0 μm in the horizontal direction. Also, we estimated the wavefront in the Fresnel diffraction field from the working distance error of a lens designed for a collimated incident beam, and showed that the working distance error, focusing spot width, and sidelobe can be improved by this estimated wavefront     

Packaging and environmental stability of thermally controlledarrayed-waveguide grating multiplexer module with thermoelectric device

We designed and fabricated arrayed-waveguide grating (AWG) modules with thermoelectric (TE) devices, and investigated their wavelength controllability and stability. The fabricated AWGs had 16 channels with a spacing of 0.8 nm in the 1.55 μm band. We confirmed that the center wavelength could be kept constant in a precise 0.02 mn range at ambient temperatures from -10 to 70°C and moreover could be tuned over a 0.35 nm range. We performed environmental tests with reference to the Bellcore requirements. These results confirmed both the stability of the AWG module under severe conditions and its mechanical strength     

TE-TM mode splitter with heterogeneously coupled Ti-diffused andNi-diffused waveguides on Z-cut lithium niobate

A coupling type mode splitter with an extraordinary polarisation and a random polarisation waveguide made by Ni and Ti indiffusion, respectively, on a Z-cut LiNbO₃ substrate is described for the first time. With optimised process parameters: a very small TM mode profile mismatch is obtained due to the similar characteristics of the Ti- and Ni-diffused waveguides. The measured extinction ratios of the TE and TM modes at 1.55 μm wavelength are >22 dB     

Continuous-wave type-II “QW” lasers emitting atλ=5.4-7.1 μm

Optically pumped type-II QW lasers emitting in the 5.4-7.1 -μm wavelength range and at continuous-wave (CW) temperatures up to 210 K are demonstrated. At 80 K, the maximum CW output power from a 40-μm-wide pump stripe is 48 mW at 5.41 μm and 31 mW at 6.05 μm. Epitaxial-side-down heat sinking is provided by a new diamond-pressure-bond mounting technique, which requires minimal processing and maintains topside optical access     

CW high power single-lobed far-field operation of long-cavityAlGaAs-GaAs single-quantum-well laser diodes grown by MOCVD

Data on long-cavity 100-μm-wide broad-stripe laser diodes that lase with a barrow single-lobed far-field pattern in continuous room-temperature operation are presented. Diodes with a cavity length of 1250 μm emit a power of 200 mW per facet into a 2.5° lobe (full width at half maximum). Short-cavity devices (cavity length of 350 μm) lase with a continuously increasing number of lateral modes right from threshold, and exhibit a far-field divergence that is over three times greater than that of 1250-μm diodes. Explanations for the effect of increasing cavity length on the field patterns of these devices are proposed, based on the measured increase in injected carrier diffusion length in long-cavity diodes and the influence of thermal waveguiding and mirror losses on intermodel discrimination     

The effect of cladding layer thickness on large optical cavity650-nm lasers

The reduction in penetration of the optical mode into the cladding layers in large optical cavity (LOC) laser structures offers the possibility of reducing the cladding-layer thickness. This could be particularly beneficial in GaInP-AlGaInP high-power devices by reducing the thermal impedance and the electrical series resistance. We have designed and characterized 650-nm LOC lasers by modeling the optical loss due to incomplete confinement of the optical mode by the cladding layers and calculating the thermally activated leakage current. This indicated that the cladding thickness could be reduced to 0.5 μm without adversely affecting performance. We investigated devices with 0.3-, 0.5-, and 1-μm-wide cladding layers. The measured optical mode loss of the 0.3-μm-wide cladding device was 36.2 cm^-1 compared with 12.4 and 11.3 cm^-1 for the 0.5- and 1-μm-wide cladding samples, respectively. The threshold current densities of the 0.5- and 1.0-μm devices were similar over the temperature range investigated (120-320 K), whereas the 0.3-μm devices had significantly higher threshold current density. We show that this can be attributed to the higher optical loss and increased leakage current through the thin cladding layer. The intrinsic gain characteristics were the same in all the devices, irrespective of the cladding-layer thickness. The measured thermal impedance of 2-mm-long devices was reduced from 30.7 to 22.3 K/W by reducing the cladding thickness from 1 to 0.5 μm. Our results show that this can be achieved without detriment to the threshold characteristics     

High-mobility CMOS transistors fabricated on very thin SOS films

It is reported that the mobility of CMOS transistors fabricated on very thin silicon-on-sapphire (SOS) films is a function of the film growth rate. Transistors with mobilities nearly as high as those obtained on 1.0-μm-thick films have been fabricated on SOS films 0.2 μm thick that have been grown at growth rates above 4 μm/min