Super compact optical add-drop multiplexer for FTTH applications based on low-loss polymer waveguide materials

Four- and eight-channel arrayed-waveguide grating (AWG) and fixed optical add-drop multiplexer (OADM) devices with channel spacing of 1200 and 600 GHz have been fabricated using super-high refractive index contrast (/spl Delta/n=0.020) triazine containing polymers. Accordingly, the size of the four-channel AWG was only 10/spl times/3 mm and the insertion loss was 3 dB.     

Germania-based core optical fibers

Germania-glass-based core silica glass cladding single-mode fibers (/spl Delta/n up to 0.143) with a minimum loss of 20 dB/km at 1.9 /spl mu/m were fabricated by the modified chemical vapor deposition (MCVD) method. The fibers exhibit strong photorefractivity with the type-IIa-induced refractive-index modulation of 2/spl times/10/sup -3/. The Raman gain of 300 to 59 dB/(km/spl middot/W) was determined at 1.07 to 1.6 /spl mu/m, respectively, in a 75 mol.% GeO/sub 2/ core fiber. Only 3 m of such fibers are enough for the creation of a 10-W Raman laser at 1.12 /spl mu/m with a 13-W pump at 1.07 /spl mu/m. Raman generation in optical fiber at a wavelength of 2.2 /spl mu/m was obtained for the first time.     

An electrostatically actuated 1/spl times/2 moving-fiber switch

A 1/spl times/2 moving-fiber switch for optical protection switching is presented. A detailed measurement of the optical performance is given. A coupling loss of 0.5 dB is achieved in the lensless optical path based on butt-coupled standard single-mode fibers. The actuation voltage is approximately 30 V. Both the electrostatic parallel-plate actuators and the fiber alignment structures are realized by anisotropic machining of crystalline silicon. This type of switch is designed for compact rows of switches.     

A reconfigurable thin-film filter-based 2 /spl times/ 2 add-drop fiber-optic switch structure

A reconfigurable 2 /spl times/ 2 add-drop fiber-optic switch structure is proposed by incorporating the independent mechanical control and alignment of an off-the-shelf thin-film filter with a reflective optical element. Cascading several 2 /spl times/ 2 add-drop switches gives a low-cost polarization-independent wavelength routing system with the limitation in optical loss that can be compensated by using optical amplifiers. The experimental result indicates a measured average optical loss of <1.30 dB at the center wavelength. In addition, the measured optical coherent crosstalk values at the center wavelength are -15 and -22 dB when the thin-film filter and the mirror are in the optical path, respectively. A very low polarization-dependent loss of <0.07 dB is also investigated.     

5/spl times/9 integrated optical star coupler in silicon-on-insulator technology

We describe fabrication of the first optical star coupler in silicon-on-insulator (SOI) technology. The 5/spl times/9 coupler consists of two silicon rib waveguide arrays with a radiative slab waveguide region. The star geometry was analyzed and designed using the beam propagation method. The coupler exhibits low loss (average excess insertion loss /spl alpha//spl sim/1.3 dB) and good coupling uniformity (standard deviation /spl sigma//spl sim/1.4 dB) at /spl lambda/=1.55 /spl mu/m. It represents a key component for realization of photonic circuits in a silicon integrated circuit technology.     

Compact polarization-insensitive InGaAsP-InP 2 /spl times/ 2 optical switch

We demonstrate a simple, compact, high-contrast ratio, and low-loss polarization-insensitive InGaAsP-InP 2 /spl times/ 2 optical switch with an operational wavelength range from 1520 to 1580 nm. The switch is 1.3 mm long by 160 /spl mu/m wide. The on-off contrast ratio is within (21/spl plusmn/2) dB over the temperature range from 16/spl deg/C to 64/spl deg/C, the polarization sensitivity is <2 dB, and the propagation loss is (3/spl plusmn/2) dB in both the ON and OFF states, making it potentially useful for optical cross-connects, delay lines, and add-drop multiplexers.     

High-power 1.5-/spl mu/m InGaAsP-InP slab-coupled optical waveguide amplifier

We report the first demonstration of a high-power semiconductor optical amplifier (SOA) based on the slab-coupled optical waveguide concept. This concept allows the realization of SOAs having large fundamental optical modes, low loss, and small optical confinement factor. These attributes support large output saturation power, long length for efficient heat removal, and direct butt-coupling to single-mode fibers. The 1.5-/spl mu/m InGaAsP-InP quantum-well amplifier described here has a length of 1 cm, 1/e/sup 2/ intensity widths of 4 /spl mu/m (vertical) and 8 /spl mu/m (horizontal), a fiber-to-fiber gain of 13 dB, and a fiber-coupled output saturation power of 630 mW (+28 dBm). The measured butt-coupling efficiency between the amplifier and SMF-28 is 55%. Thus, the output saturation power of the amplifier itself is approximately 1.1 W (+31 dBm).     

High-efficiency 1.3 /spl mu/m InAsP-GaInP MQW electroabsorption waveguide modulators for microwave fiber-optic links

High-efficiency electroabsorption waveguide modulators have been designed and fabricated using strain-compensated InAsP-GaInP multiple quantum wells at 1.32-/spl mu/m wavelength. A typical 200-/spl mu/m-long modulator exhibits a fiber-to-fiber optical insertion loss of 9 dB and an optical saturation intensity larger than 10 mW. The 3-dB electrical bandwidth is in excess of 20 GHz with a 50-/spl Omega/ load termination. When used in an analog microwave fiber-optic link without amplification, a RF link efficiency as high as -38 dB is achieved at 10 mW input optical carrier power. These analog link characteristics are the first reported using MQW electroabsorption waveguide modulators at 1.32 /spl mu/m.     

Client-configurable eight-channel optical add/drop multiplexerusing micromachining technology

A client-configurable optical add/drop multiplexer (OADM) is demonstrated using a micromachined 8×6 matrix switch. The matrix switch can be configured to add/drop any of the eight input channels from/to any of the six add/drop ports. For the switching fabric, the insertion loss is 2~3 dB for the dropped channels and 8~9 dB for the added channels by using the backsides of the micromirror switches. The switching extinction ratio is over 40 dB, the crosstalk between channels is less than -40 dB, and they are equipment-limited in this experiment     

Vertically tapered epilayers for low-loss waveguide-fiber coupling achieved in a single epitaxial growth run

Next-generation optical-communications systems require on-wafer integration of active and passive opto-electronic components to increase operating speed and reduce packaging costs. Increased coupling efficiencies between semiconductor waveguides and optical fibers are of particular interest. A simple and cost-effective method of fabricating a mode-size converter monolithically integrated with a semiconductor waveguide is presented. An on-wafer mode-size converter reduces the number of interfaces in an opto-electronic circuit and improves the coupling efficiency between semiconductor waveguide and optical fiber. Vertically tapered epilayers are deposited in a single epitaxial growth run using shadow-masked growth by chemical-beam epitaxy, avoiding complex and expensive processing and regrowth stages. Waveguides that taper vertically and horizontally over /spl sim/1 mm for gradual expansion of the mode size are demonstrated. Waveguide loss measurements showed that there was negligible loss across the tapered regions. A loss of <2 dB/interface was achieved compared with /spl sim/8 dB/interface for a butt-coupled discrete device.     

MOEMS variable optical attenuator with improved dynamic characteristics based on robust design

The design and preliminary data of a novel microoptoelectromechanical systems variable optical attenuator (VOA) driven by a pair of V-beam electrothermal actuators is described. This VOA deploys a face-to-face arranged pair of 45/spl deg/ tilted mirrors in front of two coaxially aligned lensed fibers to form retro-reflection planar light path for attenuation. The initial insertion loss is 0.7 dB at 1550 nm and the maximum dynamic range of attenuation is 50 dB, respectively. The polarization-dependent loss is measured as 0.15 dB at 20-dB attenuation. The dynamic attenuation deviation is less than /spl plusmn/0.36 dB at 20-dB attenuation with respect to 20-G shock of periodical mechanical vibration at 1 K Hz, in which it complies with requirements of the Telcordia GR1221 regulations.     

GaAs/polymer optical nanowires: fabrication and characterisation

The fabrication and propagation loss measurement of GaAs/polymer optical nanowires are reported. Their design consists of a 300/spl times/300 nm cross-section GaAs core buried into a polymer matrix bonded on a Si host substrate. The propagation loss at /spl lambda/=1.55 /spl mu/m is measured as about 5 dB/mm for both polarisations.     

Stress-induced polymer waveguides operating at both 1.31 and 1.55 /spl mu/m wavelengths

Metal-defined polymer optical waveguides have been demonstrated for the first time. A metal strip patterned on top of a polymer slab waveguide causes a stress-induced refractive index change, providing lateral optical mode confinement within the core layer. Fabricated waveguides exhibit low propagation loss values of 1.1 dB/cm at 1.31 /spl mu/m and 1.3 dB/cm at 1.55 /spl mu/m for both TE and TM polarisations.     

Integrated folding 4/spl times/4 optical matrix switch with total internal reflection mirrors on SOI by anisotropic chemical etching

A folding rearrangeable nonblocking 4/spl times/4 optical matrix switch was designed and fabricated on silicon-on-insulator wafer. To compress chip size, switch elements (SEs) were interconnected by total internal reflection (TIR) mirrors instead of conventional S-bends. For obtaining smooth interfaces, potassium hydroxide anisotropic chemical etching of silicon was utilized to make the matrix switch for the first time. The device has a compact size of 20/spl times/1.6 mm/sup 2/ and a fast response of 7.5 /spl mu/s. The power consumption of each 2/spl times/2 SE and the average excess loss per mirror were 145 mW and -1.1 dB, respectively. Low path dependence of /spl plusmn/0.7 dB in total excess loss was obtained because of the symmetry of propagation paths in this novel matrix switch.     

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.     

256/spl times/256 port optical cross-connect subsystem

This paper describes the subsystem design and performance of a 256/spl times/256-port micromechanical beam-steering optical cross-connect with 1.33-dB average loss, which can provide 238/spl times/238-port cross-connect with a maximum loss of less than 2dB. This paper describes the design chosen and analyzes the tolerance ranges required to produce low loss and simulate the expected loss distribution of the fabric. The method of establishing and testing the connections is also described. The simulation is compared with the measured system, and the expected and measured static and dynamic crosstalk are compared.     

A 32-element 8-bit photonic true-time-delay system based on a 288 /spl times/ 288 3-D MEMS optical switch

A large-scale three-dimensional microelectromechanical-system optical switch is used for the first time to realize a true-time-delay (TTD) beamformer for phased-array radar applications, with a capacity of 32 antenna elements and eight bits of delay. The 288 /spl times/ 288 optical switch has a median loss of 1.4 dB and all measured 82 944 paths exhibit less than 2.3 dB loss at 1310 nm. The TTD beamformer exhibits a loss variation of 1.5 dB, which is equalized using a mirror-offset technique.     

Low-chirp and external optical feedback resistant characteristics in /spl lambda//8 phase-shifted distributed-feedback laser diodes under direct modulation

Clarifies that phase shift value in directly modulated distributed feedback laser diodes (DFB-LDs) affects their chirp characteristics and resistance to external optical feedback because of the feedback effect of mirror loss (FEML). Comparing /spl lambda//8, /spl lambda//4, and 3//spl lambda/8 phase-shifted DFB-LDs, theoretically and experimentally, showed that the negative FEML in /spl lambda//8 phase-shifted DFB-LDs improves their transmission performance and makes them more resistant to external optical feedback. It was demonstrated with 2.5-Gb/s directly modulated 1.55-/spl mu/m /spl lambda//8 phase-shifted DFB-LDs that a very low-power penalty for 100-km transmissions (less than 1 dB for BER=10/sup -10/) can be obtained within a wide extinction ratio from 8.5 to 14.5 dB. Excellent resistance to optical feedback was also demonstrated using /spl lambda//8 phase-shifted DFB-LDs: isolator-free 80-km transmission was successful under -14-dB external optical feedback. In addition, the relation of transmission characteristics to coupling coefficient /spl kappa/L and detuning between oscillation wavelength and gain maximum was also discussed here for designing low chirp /spl lambda//8 phase-shifted DFB-LDs.     

Optical add/drop multiplexers based on X-crossing vertical couplerfilters

A simple optical add/drop multiplexer (OADM) based on a X-crossing InGaAsP-InP vertical coupler filter is demonstrated. Laterally separated input and output waveguides and the X-crossing arrangement are achieved using wafer bonding. A sidelobe level of -26 dB and a coupling efficiency of 97% with the central wavelength at 1.56 μm were measured for an OADM with an X-crossing angle of 0.25     

Gigabit/s Optical Receiver Sensitivity and Zero-Dispersion Single-Mode Fiber Transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 µm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p/sup +/nn/sup -/ Ge APD. The p/sup +/nn/sup -/ Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55 µm and a 10/sup -9/ error rate, which was 4 dB better than the receiving level with a p/sup +/n Ge APD. Detector performance at 1.3 µm was also studied for comparison with performance at 1.55 um. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55 µm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) /spl dot/ km at 1.55 µm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3 µm dispersion free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.