High-speed demonstration of single-flux-quantum cross-bar switch up to 50 GHz

We have been developing a single-flux-quantum (SFQ) cross-bar switch, which is a main component of a network packet switch. We think that a network switch is an application in which the high speed of SFQ technology would be advantageous. Anticipating general and large-scale SFQ logic circuit design, we used the cell-based design method and the CONNECT standard SFQ cell library. The two-input and two-output cross-bar switch, a core switch component, consists of 13 logic cells connected by Josephson-transmission-line (JTL) cells. Because of the large size of JTL cells and the large delay in them, timing adjustment becomes more difficult as the operating speed and circuit size increase. After using a commercially available automatic router to find appropriate routes efficiently, we used a static timing analyzer for fine timing adjustment. Timing violations were fixed by changing JTL path delays using the tools we developed. The target operating frequency of the switch was 40 GHz, which corresponds to a clock period of 25 ps. Careful timing adjustment was necessary to ensure correct operations at such a high speed. The test chip was fabricated by using an NEC standard Nb process. The circuit, including on-chip test circuitry, was composed of about 1500 Josephson junctions. We confirmed its correct operations up to 50 GHz with a bias margin of /spl plusmn/20%.     

High-density digital free-space photonic switches using micro-beam optical interconnections

We describe a compact free-space photonic-switching module that uses micro-beam optical interconnections based on stacked planar optics and exciton absorption reflection switch (EARS) arrays. The switching module has two-dimensional fiber array pigtails and a two-stage, 16-input, 16-output structure (four sets of 4/spl times/4 switches). The microbeam optical interconnections can provide a compact switching module (approximately 30/spl times/90/spl times/22 mm [60 cc]). A relay lens array inserted between stages eliminates beam spreading in the switch and decreases the coupling loss and crosstalk of interconnections. Two-stage switching at a data transmission rate of 4 Mbit/s is demonstrated.     

High-temperature operation of oxide SFQ-circuit-elements

Single flux quantum (SFQ) circuit components such as an SFQ-dc converter and a confluence buffer have been fabricated by using an YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// ramp-edge junction technology and their logic operations at temperatures up to near 60 K were investigated. The SFQ-dc converter was correctly operated in a wide temperature range from 4.2 K to 56 K and found to be useful for detecting output signals from other SFQ circuit components at any operating temperatures. The basic function that a signal from either of two input Josephson transmission lines (JTLs) was transmitted to an output JTL was confirmed for the confluence buffer and finite operating margins were obtained at temperatures from 42 K to 61 K. The narrowest margin of dc supply current obtained at temperatures from 55 K to 60 K was /spl plusmn/20% and was consistent with the simulation. Margin reduction due to thermal noise was also evaluated. According to the analytical calculation, the operating margin to keep the bit-error rate less than 10/sup -5/ was as large as /spl plusmn/20% even at 50 K when the value of junction critical-current I/sub c/ was kept near 0.4 mA.     

Fabrication of semiconductor optical switch module using laser welding technique

The 4/spl times/4, 1/spl times/2, and 1/spl times/4 semiconductor optic-switch modules for 1550 nm optical communication systems were fabricated by using the laser welding technique based on the 30-pin butterfly package. For better coupling efficiency between a switch chip and an optical fiber, tapered fibers of 10-15 /spl mu/m lens radius were used to provide the coupling efficiency up to 60%. The lens to lens distance of the assembled tapered fiber array was controlled within /spl plusmn/1.0 /spl mu/m. A laser hammering technique was introduced to adjust the radial shift, which was critical to obtain comparable optical coupling efficiencies from all the channels at the same time. The fabricated optical switch modules showed good thermal stability, with less than 5% degradation after a 200 thermal cycling. The transmission characteristics of the 4/spl times/4 switch module showed good sensitivities, providing error free transmissions below -30 dBm for all the switching paths. The dynamic ranges for the 4/spl times/4 and 1/spl times/2 switch modules were about 8 dB for a 3 dB penalty and about 17 dB for a 2 dB penalty, respectively.     

Low-power InP-HEMT switch ICs integrating miniaturized 2/spl times/2 switches for 10-Gb/s systems

This paper presents a wideband cold-FET switch with virtually zero power dissipation. The use of InP HEMTs with a low R/sub on//spl middot/C/sub off/ product enables us to configure a DC-to-over-10-GHz single-pole double-throw (SPDT) switch without using a shunt FET. The series-FET configuration offers a logic-level-independent interface and makes possible positive control voltage operation in spite of using depletion-mode FETs. A miniaturized 2/spl times/2 switch using two SPDT switches yields an insertion loss of less than 1.16 dB and isolation of more than 21.2 dB below 10 GHz, which allows us to increase the scale of the switch in a single chip easily. The add-drop operation combining two 2/spl times/2 switches in a single chip and a 4/spl times/4 switch IC integrating four 2/spl times/2 switches are presented. The packaged ICs achieve error-free operation up to 12.5 Gb/s with either positive or negative logic-level input. Extremely fast switching of /spl sim/140 ps is also successfully demonstrated.     

High-power RF switching using III-nitride metal-oxide-semiconductor heterojunction capacitors

We propose and demonstrate a novel III-Nitride high-power robust RF switch using SiO/sub 2/-AlGaN-GaN metal-oxide-semiconductor heterojunction (MOSH) capacitors. A metal electrode deposited on the top of the SiO/sub 2/ layer and the low-resistivity two-dimensional electron gas (2DEG) channel at the AlGaN-GaN interface serve as the MOSH capacitor plates. Two "back-to-back" connected MOSH capacitors form a double MOSH (D-MOSH) RF switch thereby eliminating the need for ohmic contacts and also allowing fully self-aligned fabrication. The D-MOSH switch has a symmetrical /spl pi/-type capacitance-voltage characteristic with a static ON-OFF capacitance ratio greater than 20:1. The RF switch exhibits similar polarity independent sharp /spl pi/-type transmission bias curve. At 2GHz, a single-element multifinger D-MOSH switch shows isolation greater than 25 dB and insertion loss of 0.7 dB. The switching power exceeds 60 W/mm making the novel D-MOSH switch robust device for high-power high-temperature integrated electronics.     

PetaStar: a petabit photonic packet switch

This paper presents a new petabit photonic packet switch architecture, called PetaStar. Using a new multidimensional photonic multiplexing scheme that includes space, time, wavelength, and subcarrier domains, PetaStar is based on a three-stage Clos-network photonic switch fabric to provide scalable large-dimension switch interconnections with nanosecond reconfiguration speed. Packet buffering is implemented electronically at the input and output port controllers, allowing the central photonic switch fabric to transport high-speed optical signals without electrical-to-optical conversion. Optical time-division multiplexing technology further scales port speed beyond electronic speed up to 160 Gb/s to minimize the fiber connections. To solve output port contention and internal blocking in the three-stage Clos-network switch, we present a new matching scheme, called c-MAC, a concurrent matching algorithm for Clos-network switches. It is highly distributed such that the input-output matching and routing-path finding are concurrently performed by scheduling modules. One feasible architecture for the c-MAC scheme, where a crosspoint switch is used to provide the interconnections between the arbitration modules, is also proposed. With the c-MAC scheme, and an internal speedup of 1.5, PetaStar with a switch size of 6400 /spl times/ 6400 and total capacity of 1.024 petabit/s can be achieved at a throughput close to 100% under various traffic conditions.     

Sub-/spl mu/s switching time in silicon-on-insulator Mach-Zehnder thermooptic switch

We have demonstrated both rise and fall times below 1 /spl mu/s with 10%-90% modulation in a silicon-on-insulator thermooptical Mach-Zehnder switch. The switch is based on 9-/spl mu/m-thick and 10-/spl mu/m-wide single-mode rib waveguides. Very fast switching was achieved by using a differential control method. The switch was driven with a digital signal processor accompanied by simple electronic circuitry.     

Optoelectromechanical switch array with passively aligned free-space optical components

An all-optical switch array with micro mirrors driven by electrostatic micro motors has been developed in a LIGA-technique. The system has been designed for single mode application at the telecommunication wavelength of 1.55 /spl mu/m. All fixed optical components are passively aligned inside a LIGA-structured micro optical bench. The signals are detoured inside the optical bench by means of micro mirrors, which are attached to micro wobble motors. In order to avoid angular displacements of the deflected light beams double mirrors are used. First, prototypes with 2 input and output ports have been realized. Two of these 2 /spl times/ 2 switch matrices have been integrated on a 10 /spl times/ 10 mm/sup 2/ ceramic substrate with six micro motors of 1.7 mm diameter. Switching times down to 30 ms have been achieved. The crosstalk between different channels is 90 dB. The insertion loss with passive alignment of the optical elements yielded 3 dB with a repeatability better than /spl plusmn/0.3 dB.     

A new architecture of photonic ATM switches

A photonic asynchronous transfer mode (ATM) switch architecture for ATM operation at throughputs greater than 1 Tbit/s is proposed. The switch uses vertical-to-surface transmission electrophotonic devices (VSTEPs) for the optical buffer memory, and an optical-header-driven self-routing circuit in contrast with conventional photonic ATM switches using electrically controlled optical matrix switches. The optical buffer memory using massively parallel optical interconnections is an effective solution to achieve ultra-high throughput in the buffer. In the optical-header-driven self-routing circuit, a time difference method for a priority control is proposed. For the optical buffer memory, the write and read operations to and from the VSTEP memory for 1.6 Gbit/s, 8-bit optical signal are confirmed. The optical self-routing operation and priority control operation by the time difference method in the 4×4 self-routing circuit were performed by 1.6-Gbit/s 256-bit data with a 10-ns optical header pulse     

WDM access system based on shared demultiplexer and MMF links

A wavelength-division-multiplexing (WDM) access system can be used in two basic ways: user multiplexing, which assigns a wavelength to each user, and service multiplexing, which assigns a wavelength to each service. In current designs for service multiplexing, each optical network unit (ONU) must have a demultiplexer that can select any wavelength. This paper proposes a new WDM access system that uses one demultiplexer shared by many ONUs to offer optical-distribution access services. This system realizes significant cost reductions due to its passive optical network (PON) architecture, high capacity due to its WDM technology, and easy wiring through the use of multimode fiber (MMF). As one of the realization approaches of the shared demultiplexer, we explain the principle and configuration of a shared demultiplexer based on diffraction theory, and present theoretical and experimental analyses of a prototype 4/spl times/(4/spl times/4) shared demultiplexer whose configuration is based on Littrow mounting. Experimental transmission performances demonstrate the feasibility of the proposed WDM access system.     

Development of QTAT online electronic circuit patterning system

An arbitrary pattern exposure system has been developed by employing a liquid crystal display (LCD) with 1600 /spl times/ 1200 pixels for the formation of projection images in place of a conventional reticle. The minimum pattern size becomes 11.5 /spl mu/m, which corresponds to the aperture size of each pixel on the LCD. For the purpose of quick turnaround time (TAT), the exposure system was directly connected to the circuit design system with the transmission control protocol/internet protocol network. From the experimental results on patterning of a typical electronic circuit data with the area of 46/spl times/ 46 mm, it was confirmed that the TAT from the output of design data to the finish of the exposure becomes less than 28 min. By using this system, reduction of the production cost in the printed wiring boards fabrication is expected.     

An experimental multiplier circuit based on superconducting Josephson devices

This paper describes the design, testing, and operation of a 4-bit multiplier circuit based on Josephson tunneling logic (JTL) gates. The algorithm adopted was that of a simple serial 4-bit multiplier consisting of a 4-bit adder with ripple carry, together with a four phase, 8-bit accumulator shift register. The circuit, fabricated using a 25-/spl mu/m minimum linewidth technology, operated with a minimum cycle time of 6.67 ns (a limit imposed by the external test equipment) giving a 4-bit multiplication time of 27 ns with an average power dissipation of 35 /spl mu/W per logic gate. With better external pulse generators, or internal Josephson junction generators, the present circuit has been simulated to operate with a 3.0-ns cycle giving a 4-bit multiplication time of 12 ns.     

A bipolar monolithic multigigabit/s decision circuit

A monolithic multigigabit/s decision circuit using a 0.5-/spl mu/m bipolar process technology called advanced super self-aligned technology (SST-1A) has been developed. A special decision circuit including a novel current switch based on a nonthreshold logic circuit and a cutoff prevention principle was designed and fabricated. An output voltage swing of 1 V across a 50-/spl Omega/ load, a fast transition time of 90 ps (10-90%) and 3.6 Gbit/s operation have been achieved. Power dissipation per chip is about 600 mW. This IC is applicable to very-high-speed optical fiber transmission system repeaters.     

Broadband hitless bypass switch for integrated photonic circuits

A new microphotonic hitless switch is proposed. By enabling continuous, uninterrupted transition to a bypass path, it permits tuning of wavelength add-drop filters without disturbing intermediate channels. The scheme comprises two symmetrically actuated, 2 /spl times/ 2 /spl Delta//spl beta/-type optical switches, antisymmetrically cascaded in a balanced Mach-Zehnder configuration, and a /spl pi/ differential phase shift in the interferometer arms. By symmetry, it provides for wavelength-independent hitless operation before, during and after switch reconfiguration, permitting slow switching independent of bit rate. Compact implementations using high-index-contrast microelectromechanical-system (MEMS)-actuated switches are proposed.     

Piezoelectric micro-power generation interface circuits

New power conversion circuits to interface to a piezoelectric micro-power generator have been fabricated and tested. Circuit designs and measurement results are presented for a half-wave synchronous rectifier with voltage doubler, a full-wave synchronous rectifier and a passive full-wave rectifier circuit connected to the piezoelectric micro-power generator. The measured power efficiency of the synchronous rectifier and voltage doubler circuit fabricated in a 0.35-/spl mu/m CMOS process is 88% and the output power exceeds 2.5 /spl mu/W with a 100-k/spl Omega/, 100-nF load. The two full-wave rectifiers (passive and synchronous) were fabricated in a 0.25-/spl mu/m CMOS process. The measured peak power efficiency for the passive full-wave rectifier circuit is 66% with a 220-k/spl Omega/ load and supplies a peak output power of 16 /spl mu/W with a 68-k/spl Omega/ load. Although the active full-wave synchronous rectifier requires quiescent current for operation, it has a higher peak efficiency of 86% with an 82-k/spl Omega/ load, and also exhibits a higher peak power of 22 /spl mu/W with a 68-k/spl Omega/ load which is 37% higher than the passive full-wave rectifier.     

Application of MoSi/sub 2/ to the Double-Level Interconnections of I/sup 2/L Circuits

A new MoSi/sub 2/-CVD-Al double-level interconnection system is developed to obtain a high packing density in I/sup 2/L circuits. Taking advantage of MoSi/sub 2/, a fine pattern consisting of a Iinewidth of 2.5 /spl mu/m aid a spacing of 1 /spl mu/m is achieved for the first-level interconnections. This new system has a higher reliability than the normaf Al-CVD-Al structure because of the stability of the MoSi2 surface. The fundamental properties of 1/sup2/L gates with MoSi2 interconnections, namely, gain, propagation delay time, and toggle frequency of a T flip-flop, are measured. At practical injector currents, they show nearly the same values as with Al interconnectiorm The resistance effects of MoSi/sub 2/ interconnections are calculated with regard to the unbalance of the injector currents and increase of the propagation delay time. The calculations show that these effects can be ignored at an injector current of 1 /spl mu/A/gate. At higher injector currents, the MoSi/sub 2/ interconnection resistance must be taken into account in I/sup 2/L pattern layout.     

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.     

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.