POF-based interconnects for intracomputer applications

The technology and the optical characteristics of ×8 optical interconnects based on plastic optical fibers (POF's) are presented. The MT-compatible interconnects have been realized by using ribbonized 120-1125-μm multimode step index POF. Two-dimensional POF arrays with a pitch of 250 μm have been fabricated either by using precision drilled PMMA-hole-plates or by embedding the POF's in grooved copper plates and piling them up subsequently. The transmission loss of a 20 cm-long 8×8 interconnect including two 900 bends was 1.5 dB at 650 nm, 3.5 dB at 870 nm, and 4.5 dB at 980 nm     

Polymeric optical waveguide films for short-distance opticalinterconnects

We describe three different applications of polymeric waveguide films as short-distance optical interconnects. We fabricated the waveguide films, which were 6.5 cm long and mounted in MT-compatible (MTC) connectors by passive alignment, for MM fiber systems with a 50-μm diameter graded index (GI) core. The average insertion loss of these devices was approximately 0.6 dB at 0.85-μm wavelength. We also fabricated waveguide films with a 350 mirror and an MTC connector for use as 90° out-of-plane optical deflectors, and they exhibited an insertion loss of 1 dB. Two silica planar waveguides for single-mode (SM) fiber systems were also connected by a polymeric waveguide film. Low insertion losses were obtained in both MM and SM films designed to be employed as bending waveguides. This reveals their good potential for use as practical short-distance optical interconnects     

Electromagnetic torsion mirrors for self-aligned fiber-opticcrossconnectors by silicon micromachining

We report a micromechanical fiber-optic switch (1 cm×1 cm×1 mm) based on an electromagnetically operated torsion mirror which is suitable for self-latching operation. The switch is fabricated by silicon micromachining technology, and self-alignment technique is employed to align optical fibers to the mirror. A small mirror of gold finished FeNiCo/polysilicon (150 μm×500 μm) is supported by two beams, and rotated around the axis in the magnetic field induced by an electromagnet. An incident light is redirected by the mirror in a free-space smaller than 1 mm³. Multimode fibers are used for optical coupling of small loss (-2.5 dB for reflection and -0.83 dB for transmission) at a wavelength 1.55 μm. Typical switching time is 10-25 ms, and switching contrast is larger than 45 dB. Magnetic torque and optical coupling are theoretically investigated     

Electromagnetic 2/spl times/2 MEMS optical switch

This paper presents the design, fabrication, and measurement results of a 2/spl times/2 microelectromechanical systems optical switch. The switch comprises an electromagnet and lensed fibers assembled with a micromachined movable vertical micromirror. The optical switch utilizes the out-of-plane motion of the vertical micromirror actuated by electromagnetic force compared to the comb-driven linear actuation achieved by the electrostatic force. At a wavelength of 1550 nm, the insertion loss of 0.2-0.8 dB and the polarization-dependent loss of 0.02-0.2 dB are measured. The switching time is 1 ms. A novel method of realizing a latchable optical switch using an electromagnetic actuator is also provided and verified. The latch mechanism is based on the latchability of the electropermanent magnet instead of the mechanical one using conventional arch-shaped leaf springs.     

Polymeric electrooptic 2×2 switch consisting of bifurcationoptical active waveguides and a Mach-Zehnder interferometer

We interpret the modified bifurcation optically active waveguide switch structure for a polymeric electrooptic (EO) 2×2 switch. PEI-DR1, UFC150, and Resole HM2 were used as the core EO material, the lower clad material, and the upper clad material, respectively. We present the optical and electrical properties on this material system for high-performance devices. We fabricate the electrically and optically packaged polymeric EO 2×2 switch for high-speed optical communications. At an operating voltage of 8.5 V, the crosstalk of the cross-arm is -18.1 dB, and that of the straight arm is -18.5 dB. The measured optical loss is 14 dB at λ=1.3 μm. The 6-dB attenuation in radio-frequency transmission corresponds to about 17 GHz     

High-yield external optical feedback resistant partially corrugatedwaveguide laser diodes

This paper clarifies high yield external optical feedback resistant characteristics in partially corrugated waveguide laser diodes (PC-LD's), compared to conventional distributed feedback laser diodes (DFB-LD's). Based on a novel large single dynamic analysis by combining the transient mirror loss (total net threshold gain) fluctuation with the van der Pol equations in single-mode LD's, the feedback effect of mirror loss on the external optical feedback resistance in single-mode LD's was found for the first time. Theoretical analysis predicted that in the PC-LD's, relatively stable transient mirror loss suppresses the positive feedback effect of mirror loss, as well as the optical output fluctuations under the external optical feedback. Experimental results show that the increase of the relative intensity noise in 70% PC-LD's could be suppressed to lower than -120 dB/Hz and the minimum RIN was as low as -126 dB/Hz with the external optical feedback of -20 dB     

Diode-pumped tunable Yb:YAG miniature lasers at room temperature:modeling and experiment

We present a simple design rule for diode-laser pumped quasi-three-level lasers by using the M² factor. The validity of this model was demonstrated by diode-pumped Yb:YAG laser experiments. The maximum output power of 1.33 W and optical slope efficiency of 63% were obtained in a 400-μm Yb:YAG chip miniature laser. Using a 200-μm Yb:YAG chip, a 70% optical slope efficiency was reached. In a coupled-cavity configuration, with a quartz birefringent tuning filter, 8.2 THz (29 nm) of tuning was obtained at room temperature. By changing to a calcite birefringent filter, single-axial-mode oscillation with an output power of 500 mW was observed     

A silicon MEMS optical switch attenuator and its use in lightwavesubsystems

A single-mode fiber connectorized microelectromechanical systems (MEMS) reflective optical switch attenuator operating in the 1550-nm wavelength region is described. The device consists of an electrostatically actuated gold-coated silicon vane interposed in a fiber gap yielding 0.81-dB minimum insertion loss in the transmit state and high transmission isolation in the reflection state with 2.15-dB minimum return loss. The switch attenuators also work as continuously variable optical attenuators capable of greater than 50-dB dynamic range and can be accurately regulated with a simple feedback control circuit. Switching voltages were in the range of 5-40 V and a switching time of 64 μs was achieved. The MEMS switch can be used in optical subsystems within a wavelength-division-multiplexed (WDM) optical network such as optical power regulators, crossconnects, and add/drop multiplexers. We used a discrete array of 16 switch attenuators to implement a reconfigurable 16-channel 100-GHz spacing WDM drop module of an add/drop multiplexer. Thru-channel extinction was greater than 40 dB and average insertion loss was 21 dB. Both drop-and-transmit of multiple channels (11-18-dB contrast, 14-19-dB insertion loss) and drop-and-detect of single channels (>20-dB adjacent channel rejection, 10-14-dB insertion loss) were demonstrated     

1.55-μm InP-lattice-matched VCSELs with AlGaAsSb-AlAsSb DBRs

We review the design, fabrication, and characterization of 1.55-μm lattice-matched vertical-cavity surface-emitting lasers, operating continuous wave up to 88°C. For one embodiment, the threshold current is 800 μA, the differential quantum efficiency is 23%, and the maximum output power is more than 1 mW at 20°C and 110 μW at 80°C. The basic structure consists of AlAsSb-AlGaAsSb mirrors, which provide both high reflectivity and an InP-lattice-matched structure. The quaternary mirrors have poor electrical and thermal conductivities, which can raise the device temperature. However, a double-intracavity-contacted structure along with thick n-type InP cladding layers circumvents these drawbacks and finally leads to an excellent performance. The measured voltage and thermal impedances are much lower for the intracavity-contacted device than an air-post structure in which current is injected through the Sb-based quaternary mirror. The structure utilizes an undercut aperture for current and optical confinement. The aperture reduces scattering loss at the etched mirror and contributes to high differential efficiency and low threshold current density     

A 5-V operated MEMS variable optical attenuator by SOI bulk micromachining

We report the design, fabrication, and successful demonstration of microelectromechanical variable optical attenuator (VOA) using an electrostatic microtorsion mirror (0.6 mm in diameter) combined with a fiber-optic collimator. The VOA operates at low voltages (dc 5 V or less) for large optical attenuation (40 dB, corresponding to mirror angle of 0.3/spl deg/) and a fast response time (5 ms or faster). The mirror made of a bulk-micromachined silicon-on-insulator wafer has been designed to be shock resistant up to 500 G without any mechanical failure. We also have suppressed temperature dependence of optical performance to be less than /spl plusmn/0.5 dB at 10-dB attenuation in the range of -5/spl deg/C-70/spl deg/C by mechanically decoupling the parasitic bimorph effect from the electrostatic operation.     

Tapered rib adiabatic following fiber couplers in etched GaAsmaterials for monolithic spot-size transformation

Design details and demonstration data are presented for an (Al,Ga)As monolithic tapered rib waveguide achieving modal spot-size transformation. The tapered rib adiabatic following fiber coupler structure (TRAFFIC) achieves two-dimensional (2-D) expansion of the output optical mode of single-transverse-mode semiconductor waveguide modulators and lasers using a one-dimensional (1-D) taper between noncritical initial and final taper widths which are compatible with optical lithographic techniques. Measurements are presented of total mode expansion losses between ~1.5-2.0 dB and semiconductor to single-mode-fiber waveguide coupling losses of ~0.5-1.0 dB for doped pin optical-modulator-type waveguides using the TRAFFIC waveguide. A semiconductor laser with a TRAFFIC tapered-rib mode-expansion section and measured coupling loss between the laser output and single-mode fiber of only 0.9 dB is described. Finally, a TRAFFIC Spot-size transformer for undoped waveguide modulators with total mode expansion losses of 1.84 dB and excellent modal behavior at 1.32-μm wavelength is presented. The TRAFFiC structure is particularly well suited for integration with both active and passive etched rib waveguide devices. Fabrication is relatively simple, requiring only patterning and etching of the tapered waveguide and uniform-width outer mesa waveguide without any epitaxial regrowth     

Design and analysis of single-mode oxidized VCSELs for high-speedoptical interconnects

Oxide-confined vertical-cavity surface-emitting laser diodes (VCSELs) are fabricated for applications in high-performance optical interconnects. Both 980-nm as well as 850-nm wavelength devices in one- and two-dimensional arrays are investigated. Noise properties of single- and multimode devices under different operation conditions are relative intensity noise of single-mode devices can be as low as -150 dB/Hz at output powers of about 1 mW and feedback levels up to -30 dB. Data rates up to 12.5 Gb/s with bit error rates below 10^-11 are achieved with VCSELs showing stable single-mode emission at large-signal modulation, combined with modulation bandwidths exceeding 10 GHz. Arrays with 4×8 elements flip-chip mounted on Si CMOS driver chips ready for use in parallel data transmission systems are presented     

Microoptical fiber switch for a large number of interconnects:optical design considerations and experimental realizations usingmicrolens arrays

The authors investigate a 1 × N free-space microoptical fiber switch for a large number of interconnects. The system to be studied is a reflective 4f optical system. Alignment tolerances and coupling efficiency are investigated and the benefit brought by collimating microlens arrays is reported (theoretically and experimentally). The use of microlenses enables power coupling efficiency between 3 and 2 dB (including losses due to the optical elements) for an optical switch allowing up to 3000 receiver fibers     

Ultrafast monolithic receiver OEIC composed of multimode waveguidep-i-n photodiode and HEMT distributed amplifier

A multimode waveguide p-i-n photodiode (WGPD) and a distributed baseband amplifier consisting of high-electron mobility transistors (HEMTs) were monolithically integrated on InP substrate using a stacked layer structure for both components. The multimode WGPD has a 3-dB bandwidth of 49 GHz. The distributed baseband amplifier has a 3-dB bandwidth of 47 GHz, though its 0.5-μm gate-length HEMTs have modest cutoff frequencies f_T/f_max of 47/100 GHz. The receiver optoelectronic integrated circuit has a bandwidth of 46.5 GHz. It was packaged into a fiber-pig-tailed module, and the WGPD in the module has a high responsivity of 0.62 A/W for 1.55-μm wavelength. The module achieves a sensitivity of -22.7 dBm at 40 Gb/s and exhibits a clear eye-opening at 50 Gb/s     

Realization and characterization of 8×8 resonant cavity LEDarrays mounted onto CMOS drivers for POF-based interchipinterconnections

An 8×8 array of resonant-cavity light emitting diodes (RCLED's) emitting at 980 nm and flip-chip mounted onto complimentary metal-oxide-semiconductor (CMOS) integrated drivers, is presented. The RCLED's are optimized for maximal extraction efficiency into the numerical aperture of polymer optical fibers (NA=0.5) and minimal optical crosstalk. Design of the optimal cavity structure is presented, and 8×8 arrays are realized and mounted directly onto standard CMOS chips using a solder reflow technique. The CMOS integrated drivers are designed for high-speed operation and low-power consumption, and are realized in 0.8 and 0.6-μm CMOS technology. The electrooptical modules have been realized and characterized, and over 50-μW optical power coupled to POF at 3-mA drive current is reported. Open eye diagrams at operation speed up to 250 Mb/s are presented. These characteristics are compatible with CMOS integrated low-power receivers     

Compact evanescent optical switch and attenuator withelectromechanical actuation

We report the design and the realization of an out-of-plane bending structure supporting a waveguide that is used as an optical attenuator and an optical switch. Both devices are based on evanescent field interaction induced by spatial confinement either between two waveguides or between one waveguide and an absorbing medium. The attenuator exhibits typical attenuation of 65 dB/cm. Even if the bad quality of the waveguide has prevented the correct operation of the switch, we show that the attenuation figure establishes the feasibility of a compact evanescent optical coupler with mechanical drive featuring a total length below 1 mm     

Transmission properties of hollow glass waveguides for the deliveryof CO2 surgical laser power

Hollow glass waveguides are an attractive fiber delivery system for a broad range of infrared wavelengths, including the 3-μm Er:YAG and 10.6 μm CO₂ lasers. The losses for these waveguides are as low as 0.1 dB/m at the 10.6-μm wavelength for waveguides with a 700-μm bore. The guides are suitable for delivering laser powers well in excess of 100 W. Continuous power delivery for over 250 h is possible for powers less than 35 W. When stored under normal laboratory conditions, the loss is seen to change only slightly over a period up to two years     

A 0.1 to 2.7‐GHz SOI SP8T antenna switch adopting body self‐adapting bias technique for low‐loss high‐power applications

A low‐loss high‐power single‐pole 8‐throw antenna switch adopting body self‐adapting bias technique in a 0.18‐μm thick‐film partially depleted silicon‐on‐insulator complementary metal‐oxide‐semiconductor process is implemented for multimode multiband cellular applications. A topology with symmetric port design is developed. We employ the body‐contacted field‐effect transistor to handle high power level and obtain low harmonic distortion. However, the conventional bias method for body‐contacted field‐effect transistor leads to poor insertion loss (IL), serious imbalanced voltage division, and large die size. Therefore, a new body self‐adapting bias scheme is adopted to improve the IL and power handling capability with die area reward by removing the employment of extra biasing resistor and voltage supply at the body. The presented silicon‐on‐insulator antenna switch utilizing the new body bias strategy reveals similar harmonic performance as a conventional switch version, thanks to the analogous DC bias to the gate and body, while it exhibits effectively lower IL, imbalanced voltage division, and die area. The measured IL and 0.1‐dB compression point (P_?0.1dB), at 1.9/2.7 GHz, are roughly 0.52/0.82 dB and 39.2/36.9 dBm, respectively. The overall IL and P_?0.1dB are apparently improved by approximately 0.05 to 0.13 dB and 0.5 to 0.8 dBm compared with the conventional version.     

Advances in polymer integrated optics

We report on advances in polymeric waveguide technologies developed worldwide for the telecom and datacom markets, and we describe in detail one such technology developed at AlliedSignal. Optical polymers are versatile materials that can be readily formed into planar single-mode, multimode, and microoptical waveguide structures ranging in dimensions from under a micrometer to several hundred micrometers. These materials can be thermoplastics, thermosets, or photopolymers, and the starting formulations are typically either polymers or oligomers in solution or liquid monomers. Transmission losses in polymers can be minimized, typically by halogenation, with state-of-the-art loss values being about 0.01 dB/cm at 840 nm and about 0.1 dB/cm at 1550 nm. A number of polymers have been shown to exhibit excellent environmental stability and have demonstrated capability in a variety of demanding applications. Waveguides can be formed by direct photolithography, reactive ion etching, laser ablation, molding, or embossing. Well-developed adhesion schemes permit the use of polymers on a wide range of rigid and flexible substrates. Integrated optical devices fabricated to date include numerous passive and active elements that achieve a variety of coupling, routing, filtering, and switching functions     

Terabus: Terabit/Second-Class Card-Level Optical Interconnect Technologies

In the “Terabus” optical interconnect program, optical data bus technologies are developed that will support terabit/second chip-to-chip data transfers over organic cards within high-performance servers, switch routers, and other intensive computing systems. A complete technology set is developed for this purpose, based on a chip-like optoelectronic packaging structure (Optochip), assembled directly onto an organic card (Optocard). Vertical-cavity surface emitting laser (VCSEL) and photodiode arrays (4$,times,$12) are flip-chip bonded to the driver and receiver IC arrays implemented in 0.13-$mu$m CMOS. The IC arrays are in turn flip-chip assembled onto a 1.2-cm$^2$silicon carrier interposer to complete the transmitter and receiver Optochips. The organic Optocard incorporates 48 parallel multimode optical waveguides on a 62.5-$mu$m pitch. A simple scheme for optical coupling between the Optochip and the Optocard is developed, based on a single-lens array etched onto the backside of the optoelectronic arrays and on 45$^circ$mirrors in the waveguides. Transmitter and receiver operation is demonstrated up to 20 and 14 Gb/s per channel, respectively. The power dissipation of 10-Gb/s single-channel links over multimode fiber is as low as 50 mW.