Image guide couplers used in millimeter wave integrated circuits

The dispersion and coupling characteristics of the coupled image guides are studied by using the odd-even mode principle and effective dielectric constant method. The practical design of the image guide directional couplers is presented. The experiments of 3-dB and 10-dB couplers in ka band show several good features which are very useful to millimeter wave integrated circuits with flat coupling, easy design and fabrication, mechanical stability and low losses.     

High-Q micro-ring resonators and grating couplers for silicon-on-insulator integrated photonic circuits

An ultra-small integrated photonic circuit has been proposed,which incorporates a high-quality-factor passive micro-ring resonator(MR) linked to a vertical grating coupler on a standard silicon-on-insulator(SOI) substrate.The experimental results demonstrate that the MR propagation loss is 0.532 dB/cm with a 10μm radius ring resonator,the intrinsic quality factor is as high as 202.000,the waveguide grating wavelength response curve is a 1 dB bandwidth of 40 nm at 1540 nm telecommunication wavelengths,and the measured fiber-to-fiber coupling loss is 10 dB.Furthermore,the resonator wavelength temperature dependence of the 450 nm wide micro-ring resonator is 54.1 pm/℃.Such vertical grating coupler and low loss MR-integrated components greatly promote a key element in biosensors and high-speed interconnect communication applications.     

Fast and accurate analysis of 3-D curved optical waveguide couplers

The structure-related (SR) finite-difference beam-propagation method is applied to integrated optical couplers employing curved waveguide sections. A general nonorthogonal coordinate system is introduced that matches the local structure geometry, yielding a more accurate analysis with coarser meshes than standard schemes, thus providing significant computational resource savings. Furthermore, the algorithm is easily interfaced with conventional schemes. Examples of curved two-dimensional and three-dimensional directional waveguide couplers are examined to show the advantages and generality of SR schemes as well as to explore the role of the extra degrees of freedom offered by nonorthogonal meshing.     

Blazed grating couplers on LiNbO3optical channel waveguides and their applications to integrated optical circuits

Blazed grating couplers on LiNbO3optical channel waveguides have been successfully designed, fabricated, and evaluated. A reactive ion beam etching technique was used to shape the groove profile of grating couplers. A large decay factor of 600 dB/cm along optical channel waveguide was obtained. The air coupling intensity ratio of 8:1 between positive and negative light propagation directions for ion beam angle of 55° indicated a strong blaze effect. Highly efficient optical coupling from channel waveguide to Si phototransistor was also demonstrated.     

The minimization of parasitics in integrated circuits by dielectric isolation

A radically new technique for the fabrication of integrated circuits which completely changes microelectronic design is described. In place of the back-biased pn junctions usually used for isolation of devices in a substrate, a dielectric is substituted whose properties are such that almost total isolation is achieved with no increase in area. Leakage currents are reduced by several orders of magnitude to around 10^-10amperes/cm², stray capacitances to around 10^-5pf/µ², parasitic npnp and pnpn action is eliminated, and breakdown voltage is increased up to 1000 volts. Great flexibility in the design of components is achieved through the ability to place highly conductive "wells" where needed to obtain the benefits of epitaxial techniques, and by the ability to use devices having higher breakdown voltages. The technique makes practically all circuit configurations possible, and greatly enhances the possibilities for fabrication of npn and pnp transistors in the same substrate. Some details on circuits fabricated by this technique are given, such as digital circuits with propagation delay times of 3 nanoseconds and a video amplifier with a gain-bandwidth product of over 700 Mc.     

Picosecond optical sampling of GaAs integrated circuits

Direct electrooptic sampling is a noncontact optical-probing technique for measuring with picosecond time resolution the voltage waveforms at internal nodes within GaAs integrated circuits. The factors contributing to system bandwidth, sensitivity, spatial resolution, and circuit perturbation are discussed, as are the circuit requirements for realistic testing of analog and digital devices. Measurements of high-speed GaAs integrated circuits are presented, including time-domain waveform and timing measurements of digital and analog circuits and frequency-domain transfer function measurements of microwave circuits and transmission structures     

Conception of optical integrated circuits on polymers

The authors present a successful design, realisation and characterisation of single-mode TE₀₀-TM₀₀ rib optical waveguides composed of SU-8 polymer. For the simulation, a generic software package that provides an interactive and graphical environment for analysis by polarised Semi-Vectorial Finite Difference (SVFD) method of all kinds of integrated optical waveguides, such as buried channel, raised strip, rib, embedded, or ridge waveguides, has been implemented and tested. In this method we have taken into account the terms due to the interface between each layer. After realisation of various single mode optical waveguides on SU-8 polymer and Spin on Glass (SOG) like straight, S-bends, Y-junctions, Mach-Zehnder (MZ) interferometers, the linear absorption coefficient of energy α^TE-TM of such rib waveguides have been measured and estimated, respectively, near 0.32 and 0.46 cm⁻¹ for both optical modes TE₀₀ and TM₀₀ on Si/SiO₂/SU-8 structures. These values yield optical losses of 1.36 and 2.01 dB/cm. Optical losses ascribed to Si/SiO₂/SOG/SU-8 microstructures have been evaluated to 2.33 and 2.95 dB/cm for both polarisations. Hence, as a crucial step for designing polymer components devoted to microsensors applications (pressure, heat transfert), the SU-8 polymer appears as a promising candidate for integrated optics with low optical losses.     

Time-resolved optical characterization of electrical activity in integrated circuits

If the rate of improvement in the performance of advanced silicon integrated circuits is to be sustained, new techniques for the measurement of electrical waveforms in operating circuits are needed. Critical factors dictating this requirement include the increased speed and complexity of circuits, the growing importance of faults that appear only during high-speed operation, and the use of flip-chip packaging technologies. Two recently developed all-optical methods for measuring the switching activity from the backside of a chip are described and compared. One is a passive approach based on the measurement of hot carrier luminescence emitted from the channel of a CMOS field-effect transistor (FET) during switching. The second uses a laser probe to sense the switching induced modulation of the silicon optical constants near an FET's source and drain.     

Efficient photodiode-waveguide coupling for hybrid integrated optical circuits

A GalnAsP edge-detecting photodiode was coupled with an SiO2-TiO2 single-mode waveguide in a simple hybrid integration scheme. The newly developed edge-detecting photodiode with a window region was used to improve photodiode durability.     

GaAs integrated optical circuits by wet chemical etching

An integrated optical circuit containing a laser, passive waveguide, and extra-cavity detector is described. These devices are fabricated from AlxGa1-xAs layers grown by liquid-phase epitaxy. Reflectors are formed by a two-step preferential etch procedure. For proper laser orientation on {100} wafers, the mirrors are found to be oblique, tapered so as to enhance coupling into the underlying passive waveguide; this increases the efficiency of radiation transfer to the detector. Device operation with high differential transfer efficiency and low threshold has been achieved; e.g., for devices with one etched mirror and one cleaved mirror, ηt= 16 percent andJ_{t} = 2.4kA/cm², whereas these values areeta_{t} = 6.5percent and Jt= 3.0 kA/cm²for devices with two etched mirrors. Other orientations on {100} and {110} wafers have also been investigated. The reflectivity of the etched mirrors is small,R_{e} simeq 1-2percent, but transfer efficiencies into the external passive waveguide as large asT = 50percent have been observed. The effect of small Reon device performance is examined both experimentally and theoretically. The fabrication of ribbed interconnections between active circuit components is also described.     

Transmission electron microscopy of cross sections of large scale integrated circuits

Accurate cross-sectional views of large scale integrated circuits are useful for failure analysis and process evaluation. We have successfully prepared thin sections of finished devices cut perpendicular to the plane of the chip and examined them using transmission electron microscopy. We describe the sectioning procedure and show some cross-sectional views from memory cells of a CMOS RAM with poly-Si gates and tungsten second metal. Examples include micrographs of sections through 1) an IGFET showing the gate edges and the poly-Si grain size distribution, 2) metal to Si, and metal to poly-Si contacts, and 3) poly-Si runners. Each circuit element examined was uniquely identified by mapping the cross section through adjacent memory cells and noting the sequence of elements intersected. This demonstrated ability to examine cross sections of finished devices, consisting of multilayers of materials with different densities, hardness, etc., should prove useful whenever detailed device geometries, crystalline structures, etc., need to be examined in a manner which is relatively free of experimental artifacts.     

Proposals and analyses on laser amplifier based integrated optical circuits

Simplified traveling wave laser (TWL) amplifier equations are given based on a lumped model. Pulse transfer characteristics for a TWL amplifier are examined theoretically. A new class of integrated optical amplifier with three terminals (OPATT) has been proposed as an optical analog of the electric transistor. Analytical formulas and dynamic properties of an OPATT have been considered. OPATT-based optical integrated circuits, including optical differential amplifiers, comparators, saturable oscillators, and optical logic gates, have been investigated theoretically.     

n-p-n silicon lateral phototransistors for hybrid integrated optical circuits

An etched mesa silicon lateral phototransistor (EMS-LPT) suitable for detecting the light signal from optical channel waveguides has been designed and fabricated. In this paper both n⁺-p-n⁺uniform base and n⁺-p-p^--n⁺double-diffused EMS-LPT's are reported. The photoactive region of the EMS-LPT is highly localized and can be easily coupled either via an evanescent field or to a grating coupler on a channel waveguide. Light coupling, gain, speed, and signal-to-noise ratio of the device are thereby greatly improved. The fabrication techniques of the EMS-LPT's are compatible with those of MOSFET's, permitting integration of multiple EMS-LPT's and MOSFET load transistors to form optically addressed inverters on the same silicon chip. By flip-chip bonding LiNbO3and silicon substrates and coupling LiNbO3channel waveguides to EMS-LPT's via grating couplers, we produce electrooptic switches with optical input and output.     

Nondestructive optical technique for electrically testing insulated-gate integrated circuits

A simple nondestructive optical technique for electrically testing insulated-gate integrated circuits and for testing dielectric layers for pinholes and breakdown strength is described using a nematic liquid crystal in the dynamic scattering mode. Good correlation has been obtained between this technique and conventional electrical-probe test results. The technique has also proved particularly useful for fault locating and diagnosis.     

Liquid crystal variable optical attenuators integrated on planarlightwave circuits

Variable optical attenuators using polymer-network liquid crystal have been integrated with the pitch of 250 μm on planar lightwave circuits. Trenches are cut in the direction perpendicular to the parallel light waveguides into planar lightwave circuits, a transparent electrode is deposited inside the trenches, and the trenches are filled with polymer-network liquid crystal. The typical attenuation range is 18 dB when the driving voltage is <20 Vrms at 1.55-μm wavelength. The power consumption is estimated to be very low (200 nW/ch)     

Three-guide optical couplers in GaAs

Three-guide optical couplers consisting of three 4.75-μm-wide slab-coupled rib guides separated by 4.25μm have been fabricated in GaAs. The performance of these couplers at 1.28 μm is in close agreement with that predicted using a modified effective-index method to obtain an approximate analytical solution for this type of coupler. The coupling length needed to symmetrically transfer power from the center guide to the two outside guides was 3.2 mm. At this length, less than 1 percent of the power remained in the center guide. The length needed to transfer power from one outside guide to the other outside guide was ≈ 6.4 mm, which isapprox sqrt{2}- times that of a similar two-guide coupler and twice that required to couple power from the center guide to the two outside guides. The power transfer efficiency in this case is not as good as when power was inputted into the center guide. Three-guide couplers of this type should prove useful as power dividers and combiners, especially in cases where waveguide bend losses preclude the use of"Y"- junctions. They may also prove useful as replacements for two-guide couplers where either sharper transfer characteristics are desired or where losses due to waveguide bends are again unacceptable.     

Silicon-based optical receivers in BiCMOS technology for advanced optoelectronic integrated circuits

A double photodiode (DPD) and a phototransistor were implemented in an industrial 0.8 μm bipolar complementary metal oxide semiconductor (BiCMOS) n-well process. Both devices are 100% BiCMOS compatible, so that no process modifications were necessary. A −3 dB bandwidth of more than 200 MHz was measured for the DPD. The rise and fall times of the photodiode are less than 1 ns. By an optimized antireflection coating layer for a wavelength of 638 nm a quantum efficiency of η=95%, which corresponds to a responsivity of R=0.49 A/W, is achievable. A phototransistor with a light-sensitive area of 53×53 μm² was developed. Its current amplification of B=300 results in a much larger responsivity compared to the photodiodes. Measurements have shown a −3 dB bandwidth of 7.8 MHz for the phototransistor.     

Efficient finite-element-based time-domain beam propagation analysis of optical integrated circuits

In this paper, a novel numerically efficient time-domain beam propagation method based on the versatile finite element method (FETDBPM) is presented for the analysis of arbitrarily shaped optical integrated circuits. Lumping the global mass matrix into a diagonal matrix, an explicit full band finite-element time-domain propagation algorithm that needs only matrix-vector multiplication at each time step is derived. The accuracy and efficiency of the proposed FETDBPM is demonstrated through the analysis of propagation in different photonic integrated structures.     

Power exchange in tapered optical couplers

The power exchange between nonparallel optical waveguides or tapered couplers is analyzed by the coupled-mode theory based on local modes of the individual waveguides (local waveguide modes). A self-consistent nonorthogonal coupled-mode formulation is presented and transformed into an orthogonal form which is equivalent to the coupled-mode equations for the local modes of the coupled waveguides (local array modes). The coupled-mode equations are then solved numerically and the effect of the taper on the power exchange between the two guides is studied     

Improved tolerance in optical directional couplers

Tolerance requirements in conventional synchronous-mode directional couplers are examined. It is proposed that the tolerance situation can be improved considerably by tapering one, or both, of the propagation coefficients, so that they intersect at one position. This model is examined numerically, and suggestions are made for the practical realisation of a device.