Low-cost 1.55-/spl mu/m InGaAsP-InP spot size converted (SSC) laser with conventional active layers

We report the realization of a low cost 1.55-/spl mu/m spot size converted (SSC) laser using conventional SCH-MQW active layers. The laser consists of a rectangular gain section, a linear taper and a passive waveguide. The lateral taper and the passive waveguide are fabricated on the same lower SCH layer, using conventional photolithography and RIE (reactive ion etching). The device exhibits low beam divergence of 6.6/spl deg//spl times/10.9/spl deg/ and -2.2-dB coupling loss with a cleaved single-mode fiber. The 1-dB alignment tolerance is /spl plusmn/2.15 /spl mu/m in vertical direction and /spl plusmn/2.3 /spl mu/m in lateral direction, respectively.     

High-temperature and high-speed operation of a 1.3-/spl mu/m uncooled InGaAsP-InP DFB laser

1.3-/spl mu/m uncooled InGaAsP-InP loss-coupled distributed feedback lasers operating over 10 Gb/s and at 85/spl deg/C were successfully fabricated. In order to achieve high-speed and high-temperature operation simultaneously, the following are thoroughly investigated: modulation-doped and strain-compensated multiple-quantum-well active layers, Fe-doped buried-heterostructure, coupling coefficient of loss-coupled grating, detuning lasing wavelength from the gain peak, and facet coatings. The authors also demonstrate 10 Gb/s transmission with negligible dispersion power penalty over 20 km of nondispersion-shifted fiber at 10 Gb/s for temperatures ranging from 25/spl deg/C to 85/spl deg/C.     

PCB-compatible optical interconnection using 45/spl deg/-ended connection rods and via-holed waveguides

In this paper, a new architecture for a chip-to-chip optical interconnection system is demonstrated that can be applied in a waveguide-embedded optical printed circuit board (PCB). The experiment used 45/spl deg/-ended optical connection rods as a medium to guide light paths perpendicularly between vertical-cavity surface-emitting lasers (VCSELs), or photodiodes (PDs) and a waveguide. A polymer film of multimode waveguides with cores of 100/spl times/65 /spl mu/m was sandwiched between conventional PCBs. Via holes were made with a diameter of about 140 /spl mu/m by CO/sub 2/-laser drilling through the PCB and the waveguide. Optical connection rods were made of a multimode silica fiber ribbon segment with a core diameter of 62.5 and 100 /spl mu/m. One end of the fiber segment was cut 45/spl deg/ and the other end 90/spl deg/ by a mechanical polishing method. These fiber rods were inserted into the via holes formed in the PCB, adjusting the insertion depth to locate the 45/spl deg/ end of rods near the waveguide cores. From this interconnection system, a total coupling efficiency of about -8 dB was achieved between VCSELs and PDs through connection rods and a 2.5 Gb/s /spl times/ 12-ch data link demonstrated through waveguides with a channel pitch of 250 /spl mu/m in the optical PCB.     

Uncooled 1.3-/spl mu/m complex-coupled DFB BH laser diodes with the Fe-doped InGaAsP-InP hybrid current-blocking grating

In this letter, we proposed an alternate method by using the Fe-doped InGaAsP-InP hybrid grating layers to fabricate the 1.3-/spl mu/m current-blocking-grating complex-coupled distributed-feedback (CBG CC-DFB) laser diodes (LDs) grown by metal-organic chemical vapor deposition (MOCVD). By combining the Fe-doped InGaAsP-InP grating layers, the CBG CC-DFB LDs can provide high optical DFB coupling coefficient and high current confining ability. Moreover, the current aperture in the lateral direction can be easily controlled by the self-aligned MOCVD regrowth process. Therefore, the manufacture of CBG CC-DFB buried heterostructure LDs is easy as the ridge-waveguide LDs. The LDs exhibit a low threshold current of 5.3 mA, a high slope efficiency of 0.42 mW/mA, and a stable single mode with a high sidemode suppression ratio of /spl sim/42 dB at two times the threshold (10.5 mA). Even at high temperatures, these LDs still have an extremely low threshold current of 15.8 mA at 90/spl deg/ and a small variation in slope efficient of only -1 dB at the temperatures between 20/spl deg/ and 80/spl deg/. Furthermore, these LDs show a high-speed characteristic of more than 11.8 GHz at 20/spl deg/, which are suitable for 10-Gb/s Ethernet and OC-192 applications.     

Polymeric 2/spl times/2 electrooptic switch consisting of asymmetric Y junctions and Mach-Zehnder interferometer

2/spl times/2 electrooptic switches consisting of a pair of asymmetric Y junctions and Mach-Zehnder interferometer have been demonstrated in polymeric waveguides. The switching voltage is 15 V with 1.5 cm long electrode for TM polarized light at 1.3 /spl mu/m. When the branching angle of the asymmetric Y junction is 0.2/spl deg/, crosstalk of -27 to -22 dB are obtained for both input arms. The measured insertion loss by the lens coupling is about 9-10 dB.     

Stability of amorphous-silicon TFTs deposited on clear plastic substrates at 250/spl deg/C to 280/spl deg/ C

Amorphous-silicon (a-Si) thin-film transistors (TFTs) were fabricated on a free-standing new clear plastic substrate with high glass transition temperature (T/sub g/) of >315/spl deg/ C and low coefficient of thermal expansion of <10 ppm/ /spl deg/ C. Maximum process temperatures on the substrates were 250/spl deg/C and 280/spl deg/C, close to the temperatures used in industrial a-Si TFT production on glass substrates. The first TFTs made at 280/spl deg/C have dc characteristics comparable to TFTs made on glass. The stability of the 250/spl deg/C TFTs on clear plastic is approaching that of TFTs made on glass at 300/spl deg/C-350/spl deg/C. TFT characteristics and stability depend only on process temperature and not on substrate type.     

The thermal stability of one-transistor ferroelectric memory with Pt-Pb/sub 5/Ge/sub 3/O/sub 11/-Ir-poly-SiO/sub 2/-Si gate stack

The thermal stability of one-transistor ferroelectric nonvolatile memory devices with a gate stack of Pt-Pb/sub 5/Ge/sub 3/O/sub 11/-Ir-Poly-SiO/sub 2/-Si was characterized in the temperature range of -10/spl deg/C to 150/spl deg/C. The memory windows decrease when the temperatures are higher than 60/spl deg/C. The drain currents (I/sub D/) after programming to on state decrease with increasing temperature. The drain currents (I/sub D/) after programming to off state increase with increasing temperature. The ratio of drain current (I/sub D/) at on state to that at off state drops from 7.5 orders of magnitude to 3.5 orders of magnitude when the temperature increases from room temperature to 150/spl deg/C. On the other hand, the memory window and the ratio of I/sub D/(on)/I/sub D/(off) of the one-transistor memory device displays practically no change when the temperature is reduced from room temperature to -10/spl deg/C. One-transistor (1T) memory devices also show excellent thermal imprint properties. Retention properties of 1T memory devices degrade with increasing temperature over 60/spl deg/C.     

Effect of Mg doping on the superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta//

Superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta// (Cu/sub 1-x/Tl/sub x/Mg/sub y/-1234) material have been studied in the composition range y=0,1.5,2.25. The zero resistivity critical temperature [T/sub c/(R=0)] was found to increase with the increased concentration of Mg in the unit cell; for y=1.5 [T/sub c/(R=0)]=131 K was achieved which is hitherto highest in Cu/sub 1-x/Tl/sub x/-based superconductors. The X-ray diffraction analyses have shown the formation of a predominant single phase of Cu/sub 0.5/Tl/sub 0.5/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta// superconductor with an inclusion of impurity phase. It is observed from the convex shape of the resistivity versus temperature measurements that our as-prepared material was in the region of carrier over-doping, and the number of carriers was optimized by postannealing experiments in air at 400/spl deg/C, 500/spl deg/C, and 600/spl deg/C. The T/sub c/(R=0) was found to increase with postannealing and the best postannealing temperature was found to be 600/spl deg/C. The mechanism of increased T/sub c/(R=0) is understood by carrying out infrared absorption measurements. It was observed through softening of Cu(2)-O/sub A/-Tl apical oxygen mode that improved interplane coupling was a possible source of enhancement of T/sub c/(R=0) to 131 K.     

Characterization of the temperature sensitivity of gain and recombination mechanisms in 1.3-/spl mu/m AlGaInAs MQW lasers

The potential of 1.3-/spl mu/m AlGaInAs multiple quantum-well (MQW) laser diodes for uncooled operation in high-speed optical communication systems is experimentally evaluated by characterizing the temperature dependence of key parameters such as the threshold current, transparency current density, optical gain and carrier lifetime. Detailed measurements performed in the 20/spl deg/C-100/spl deg/C temperature range indicate a localized T/sub 0/ value of 68 K at 98/spl deg/C for a device with a 2.8 /spl mu/m ridge width and 700-/spl mu/m cavity length. The transparency current density is measured for temperatures from 20/spl deg/C to 60/spl deg/C and found to increase at a rate of 7.7 A/spl middot/cm/sup -2//spl middot/ /spl deg/C/sup -1/. Optical gain characterizations show that the peak modal gain at threshold is independent of temperature, whereas the differential gain decreases linearly with temperature at a rate of 3/spl times/10/sup -4/ A/sup -1//spl middot//spl deg/C/sup -1/. The differential carrier lifetime is determined from electrical impedance measurements and found to decrease with temperature. From the measured carrier lifetime we derive the monomolecular ( A), radiative (B), and nonradiative Auger (C) recombination coefficients and determine their temperature dependence in the 20/spl deg/C-80/spl deg/C range. Our study shows that A is temperature independent, B decreases with temperature, and C exhibits a less pronounced increase with temperature. The experimental observations are discussed and compared with theoretical predictions and measurements performed on other material systems.     

A CMOS smart temperature sensor with a 3/spl sigma/ inaccuracy of /spl plusmn/0.5/spl deg/C from -50/spl deg/C to 120/spl deg/C

A low-cost temperature sensor with on-chip sigma-delta ADC and digital bus interface was realized in a 0.5 /spl mu/m CMOS process. Substrate PNP transistors are used for temperature sensing and for generating the ADC's reference voltage. To obtain a high initial accuracy in the readout circuitry, chopper amplifiers and dynamic element matching are used. High linearity is obtained by using second-order curvature correction. With these measures, the sensor's temperature error is dominated by spread on the base-emitter voltage of the PNP transistors. This is trimmed after packaging by comparing the sensor's output with the die temperature measured using an extra on-chip calibration transistor. Compared to traditional calibration techniques, this procedure is much faster and therefore reduces production costs. The sensor is accurate to within /spl plusmn/0.5/spl deg/C (3/spl sigma/) from -50/spl deg/C to 120/spl deg/C.     

Second generation I/SUP 2/L/MTL: a 20 ns process/structure

A high performance, second generation I/SUP 2/L/MTL gate for digital LSI applications with TTL compatibility has successfully been designed, characterized, and demonstrated fully functional over a wide current range and the military temperature range of -55 to 125/spl deg/C. Performance is measured using an in-line five-collector gate having one end injector. The gate performed with the following characteristics at 100 /spl mu/A injector current: /spl beta//SUB U//SUP eff//spl ges/4 for all collectors at 25/spl deg/C and /spl ges/2.5 at -55/spl deg/C, /spl alpha//SUB rec///spl alpha//SUB F//spl cong/0.58 and /spl tau/~/SUB d/=18-20 ns from -55 to 125/spl deg/C, and a speed-power product of 1.4 pJ at 25/spl deg/C. At low injector currents, a constant speed-power product of 0.36 pJ at 25/spl deg/ was obtained.     

Fabrication and characterization of polymer optical waveguides with integrated micromirrors for three-dimensional board-level optical interconnects

This paper describes the fabrication and characterization of optical/electrical printed circuit boards (O/E-PCB) with embedded multimodal step index (MM-SI) waveguides and integrated out-of-plane micromirrors (IMMs) for three-dimensional (3-D) optical interconnects. Optical circuitry is built up on PCBs using UV lithography; 45/spl deg/ input/output (I/O) couplers are fabricated by inclined exposure. Commercial polymers are used as optical core and cladding materials. Critical mirror properties of angle, surface quality, reflectivity, and coupling efficiency are characterized experimentally and theoretically. Optical and scanning electron microscopy, white light interferometry, and fiber scanning method are used in the investigations. Sloping profiles measured as a function of the incident light showed the attainment of mirror angles of /spl alpha/=36/spl deg/-45/spl deg/ with /spl plusmn/2/spl deg/ consistency. Near-field optical imaging with a white light source showed that out-of-plane beam turning was achieved. Topography investigations revealed a rectilinear negative tapering shape regardless of the incoming beam angle or type of substrate. However, higher substrate reflectancy was observed to lower the mirror angle. The average propagation loss measured for 10-cm-long waveguides at /spl lambda/=850 nm by the cut-back method was 0.60 dB/cm; the excess loss calculated for the mirror coupling was 1.8-2.3 dB. The results showed that the IMMs can be incorporated in O/E-PCBs to couple light in and out of planar waveguides. Furthermore, the presented results indicate that optical waveguides with integrated micromirrors for optical 3-D wiring can be produced compatible with volume manufacturing techniques.     

360/spl deg/ Varactor Linear Phase Modulator

Theory is presented which 1) derives the circuit impedance requirements to match the nonlinearity of the varactor reactance-versus-voltage curve to the tangent /spl theta/ curve to obtain 180/spl deg/ linear phase modulation from one diode; 2) gives the value and position of a resistor to make insertion loss invariant with phase; and 3) derives the circuit requirements for combining two 180/spl deg/ diode phase moduIators in an admittance adding network to obtain 360/spl deg/ phase modulation. Experiments are disclosed rising series tuning at 1 GHz providing 360/spl deg/ phase modulation within /spl plusmn/ 3.0 percent of linearity, and using shunt tuning at 5 GHz providing 360/spl deg/ phase modulation within /spl plusmn/ 3.3 percent of linearity. A discussion is given of the application of the modulators to the serrodyne function.     

Modeling and control of a six-axis precision motion control stage

This work presents a newly developed six-axis magnetic suspension stage for precision motion control. The designed travel volume is 4/spl times/4/spl times/2 mm in translation and 1/spl deg//spl times/1/spl deg//spl times/2/spl deg/ in rotation. A dynamic model of the feedback linearized and uncoupled stage is developed for the purpose of motion control. Model parameter variations are demonstrated through closed-loop system identification. In motion control, a parameter variation model is proposed in conjunction with a reduced order observer to compensate the joined effect of disturbance, modeling error, and cross coupling. Experimental results in terms of positioning stability, motion resolution, rotational motion control, model regulation, large travel multiaxis contouring, and disturbance rejection are shown. Uniform positioning stability and invariant dynamic response within the designed travel volume are illustrated.     

Low-threshold high-T/sub 0/ 1.3-/spl mu/m InAs quantum-dot lasers due to p-type modulation doping of the active region

P-type doping is used to demonstrate high-To, low-threshold 1-3 /spl mu/m InAs quantum-dot lasers. A 5-/spl mu/m-wide oxide confined stripe laser with a 700-/spl mu/m-long cavity exhibits a pulsed T/sub 0/ = 213 K (196 K CW) from 0/spl deg/C to 80/spl deg/C. At room temperature, the devices have a CW threshold current of /spl sim/4.4 mA with an output power over 15 mW. The threshold at 100/spl deg/C is 8.4 mA with an output power over 8 mW.     

Thermally stable Ge/Ag/Ni Ohmic contact for InAlAs/InGaAs/InP HEMTs

Excellent annealed ohmic contacts based on Ge/Ag/Ni metallization have been realized in a temperature range between 385 and 500/spl deg/C, with a minimum contact resistance of 0.06 /spl Omega//spl middot/mm and a specific contact resistivity of 2.62 /spl times/10/sup -7/ /spl Omega//spl middot/cm/sup 2/ obtained at an annealing temperature of 425/spl deg/C for 60 s in a rapid thermal annealing (RTA) system. Thermal storage tests at temperatures of 215 and 250/spl deg/C in a nitrogen ambient showed that the Ge/Ag/Ni based ohmic contacts with an overlay of Ti/Pt/Au had far superior thermal stabilities than the conventional annealed AuGe/Ni ohmic contacts for InAlAs/InGaAs high electron mobility transistors (HEMTs). During the storage test at 215/spl deg/C, the ohmic contacts showed no degradation after 200 h. At 250/spl deg/C, the contact resistance value of the Ge/Ag/Ni ohmic contact increased only to a value of 0.1 /spl Omega//spl middot/mm over a 250-h period. Depletion-mode HEMTs (D-HEMTs) with a gate length of 0.2 /spl mu/m fabricated using Ge/Ag/Ni ohmic contacts with an overlay of Ti/Pt/Au demonstrated excellent dc and RF characteristics.     

400 mW uncooled MiniDIL pump modules

A new generation of wavelength stabilised, uncooled 980 nm pump modules in MiniDIL housings is presented, enabling 400 mW ex-fibre power over a temperature range of 10/spl deg/C to 70/spl deg/C. At 100/spl deg/C 200 mW power is still obtained with a robust fibre coupling scheme.     

45/spl deg/ slanted fibre Bragg grating design with prism coupled holographic exposure

A holographic technique for forming 45/spl deg/ tilted fibre gratings using two 45/spl deg/-90/spl deg/, -45/spl deg/ fused silica prisms is described. The technique reduces fringe distortion due to the lens effects of the fibre during exposure. Details of the experimental system and grating performance are given.     

Low threshold current 1.3-/spl mu/m GaInNAs VCSELs grown by MOVPE

The structure of the conventional contact 1.3-/spl mu/m GaInNAs-GaAs vertical-cavity surface-emitting lasers (VCSELs) was optimized and low threshold current 1.3-/spl mu/m GaInNAs VCSELs grown by metal-organic vapor-phase epitaxy were reported. The idea is to optimize the active region, the doping profiles, and the pairs of p-distributed Bragg reflectors, and the detuning between the emission wavelength and the photoluminescence gain peak wavelength. The continuous-wave 1.0-mA threshold current was achieved for the single-mode VCSEL. For the multiple-mode VCSELs, the below 2-mA threshold currents at 5/spl deg/C-85/spl deg/C , the 1.13-mA threshold current at 55/spl deg/C, and 1.52-mA threshold current at 85/spl deg/C are the best results for 1.3-/spl mu/m GaInNAs VCSELs.     

A 14-bit high-temperature /spl Sigma//spl Delta/ modulator in standard CMOS

Experimental verification is given for the use of /spl Sigma//spl Delta/ modulation for high-temperature applications (/spl ges/approximately 150/spl deg/C) in a standard CMOS process. Switched-capacitor circuits are used to implement a second-order single-stage and a third-order 2-1 MASH /spl Sigma//spl Delta/ modulator with single-bit quantization. The two modulators have an oversampling ratio of 256 with an input signal bandwidth of 500 Hz. The modulators were fabricated in a 1.5-/spl mu/m standard CMOS technology. A fully differential signal path and near minimum sized switches are used to mitigate the effect of large junction-to-substrate leakage current present at high temperatures. Experimental results show both modulators are capable of over 14 bits of resolution at 225/spl deg/C and over 13 bits of resolution at 255/spl deg/C. Results show that the single-stage modulator is more resistant to high-temperature circuit impairment than is the MASH cascaded structure.