A thin-film filter-based 1/spl times/2 reconfigurable fiber-optic add-drop module with a quadruple fiber-optic collimator

Due to a limited optical crosstalk in most thin-film filter (TF)-based fiber-optic modules, we propose and experimentally verify a low optical crosstalk TF-based 1/spl times/2 reconfigurable fiber-optic add-drop structure. Our key idea is to employ a passive noise rejection scheme by introducing a double reflection on the TF as well as a spatial separation through a combination of a quadruple and a single fiber-optic collimators. Our experimental results show a much improved <-39.1-dB optical crosstalk at the Thru port. In addition, the measured average optical losses at the Drop and the Thru ports are 1.40 and 1.23 dB, respectively, when the TF is in the optical path. When the mirror is in the optical path, all wavelength optical beams are directed to the Thru port with a measured average 2.50-dB optical loss. A low polarization-dependent loss of <0.17 dB is also determined. Furthermore, our design concept can be used to form a low optical crosstalk fixed three-port add-drop filter and a high dynamic-range wavelength-sensitive variable fiber-optic attenuator.     

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.     

2/spl times/4 optical add-drop module with no difference in propagation length

We developed a micromachined X-type 2/spl times/4 optical add-drop module (OADM) featuring no difference in propagation length. Four pairs of lensed fibers are aligned in "X" position, and four micromirrors are located between the pairs of optical fibers. The OADM was fabricated utilizing a silicon-on-insulator process. Electrostatic comb actuators can be driven up to 90 /spl mu/m to change the light path within 1 ms. The insertion loss and the on-off ratio were less than 3 and 70 dB, respectively. The loss uniformity in every channel was 1.5 dB.     

A Thin-Film Filter-Based 1$, times,$2 Reconfigurable Fiber-Optic Add&#8211;Drop Module With a Quadruple Fiber-Optic Collimator

Due to a limited optical crosstalk in most thin-film filter (TF)-based fiber-optic modules, we propose and experimentally verify a low optical crosstalk TF-based 1$, times,$2 reconfigurable fiber-optic add–drop structure. Our key idea is to employ a passive noise rejection scheme by introducing a double reflection on the TF as well as a spatial separation through a combination of a quadruple and a single fiber-optic collimators. Our experimental results show a much improved$≪ - $39.1-dB optical crosstalk at the Thru port. In addition, the measured average optical losses at the Drop and the Thru ports are 1.40 and 1.23 dB, respectively, when the TF is in the optical path. When the mirror is in the optical path, all wavelength optical beams are directed to the Thru port with a measured average 2.50-dB optical loss. A low polarization-dependent loss of$≪$0.17 dB is also determined. Furthermore, our design concept can be used to form a low optical crosstalk fixed three-port add–drop filter and a high dynamic-range wavelength-sensitive variable fiber-optic attenuator.     

Reconfigurable Add–Drop Optical Filter Based on Arrays of Digital Micromirrors

We demonstrate a universal reconfigurable add-drop optical filter based on arrays of digital micromirrors. Our approach allows for reconfiguration of the device parameters for operation in different sets of channel wavelengths, even or uneven channel-to-channel separation, adjustable channel passband, and dynamic add-drop of optical signals. The proposed device shows insertion loss at the center wavelength in the all-pass configuration of 7.6 dB, extinction ratio of 35 dB, channel isolation better than 24dB, negligible loss ripple, and possibility of reconfiguration time in the order of microseconds. Although designed for demonstration on optical telecommunication frequencies, the high-flexibility features of the proposed add-drop filter allow it to be used for other optical wavelength-based filtering/switching applications.     

Polarisation-insensitive Si/sub 3/N/sub 4/ strip-loaded BaTiO/sub 3/ thin-film waveguide with low propagation losses

A low-loss and polarisation-insensitive singlemode BaTiO/sub 3/ thin-film waveguide is reported. Polarisation-dependent loss as low as 0.1 dB/cm at a wavelength of 1.55 /spl mu/m has been achieved by a novel Si/sub 3/N/sub 4/ strip-loaded BaTiO/sub 3/ waveguide structure. Propagation loss of less than 0.9 dB/cm for both TE and TM polarisations was measured     

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.     

All-fiber wavelength-tunable acoustooptic switches based on intermodal coupling in fibers

In this paper, we demonstrate a novel all-fiber wavelength-tunable acoustooptic switch utilizing intermodal coupling in a two-mode fiber (TMF). Its all-fiber configuration consisting of a fiber acoustooptic tunable filter and a mode-selective coupler results in the low loss (<2 dB) operation. The operating bandwidth >50 nm, the switching time of 40 /spl mu/sec, and the crosstalk of 20 dB were achieved. By controlling the design parameters of the two-mode fiber, the 3-dB bandwidth of the switched signal was varied from 2.5 nm to >35 nm. A novel all-fiber dynamic optical add-drop multiplexer is also demonstrated using two acoustooptic switches in series.     

Low-cost WDM-PON with colorless bidirectional transceivers

This paper presents a low-cost bidirectional (BiDi) wavelength-division-multiplexed passive optical network (WDM-PON) employing colorless uncooled BiDi transceivers (TRxs) and superluminescent diode (SLD)-based broadband light sources (BLSs). The C band is allocated for upstream and the E+ band for downstream in consideration of BiDi packaging, SLD development, and wavelength alignment of dual-window arrayed waveguide gratings (AWGs). The BiDi TRx integrates an uncooled Fabry-Perot laser diode (FP-LD), a p-i-n photodiode (PD), and a 45/spl deg/-angled thin-film filter in a small-form-factor (SFF) package. The SLD-based BLSs provide 13-dBm amplified spontaneous emissions (ASEs) with spectral ripples of < 3 dB and polarization dependencies of <1 dB. Colorless operations over 32 100-GHz-spaced channels are demonstrated from -20 to 80/spl deg/C in 155-Mb/s BiDi transmissions over 25 km.     

Narrow passband high-temperature superconducting filters of highly compact sizes for personal communication service applications

A novel highly compact high-temperature superconducting filter based on spiral lumped elements was demonstrated for personal communication system applications. The filter consists of eight-pole microstrip resonators enclosed in a substrate 0.5 /spl times/ 5 /spl times/ 32 mm. The filter was designed to have a bandwidth of 17 MHz and a center frequency of 1760 MHz. A low insertion loss of 0.4 dB in the passband with an out-of-band rejection loss of about -70 dB was observed at 65 K. Measured characteristics of the filter showed good agreement with simulated responses.     

Low crosstalk 1/spl times/2 thermooptic digital optical switch with integrated S-bend attenuator

We propose and demonstrate a 1/spl times/2 thermooptic digital optical switch with variable optical attenuators that are integrated with the S-bend waveguides connecting the output of the Y-switch with a standard fiber array. With a total heating power of 140 mW applied to the switch, we have achieved less than -42-dB optical crosstalk. The wavelength response of the switch is flat across the entire C-band. The average polarization-dependent loss of the switch is about 0.49 dB.     

Wavelength multiplexer based onSiO2-Ta2O5 arrayed-waveguide grating

The characteristics of a wavelength multiplexer based on an arrayed-waveguide grating are carefully investigated by using the grating theory and related experiments. A 28-channel multiplexer is designed and fabricated as SiO₂-Ta₂O₅ waveguides on a 1 cm×2 cm substrate. The designed wavelength channel spacing of 1 nm is obtained. The crosstalk to an adjacent channel is -15 dB. The measured minimum loss is 4.2 dB, which is composed of 3.4 dB excess loss and 0.8 dB grating loss     

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.     

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.     

Peripheral-coupled-waveguide MQW electroabsorption modulator for near transparency and high spurious free dynamic range RF fiber-optic link

Peripheral coupled waveguide (PCW) design has been deployed in InGaAsP multiple quantum-well (MQW) electroabsorption modulator (EAM) at 1.55-/spl mu/m wavelength. PCW enhances the optical saturation power and reduces the optical insertion loss and the equivalent V/sub /spl pi// simultaneously. A radio-frequency link using a 1.3-mm-long lumped-element PCW EAM has achieved experimentally a link gain of -3 dB, at 500 MHz and at input optical power of 80 mW. The corresponding two-tone multioctave spurious-free dynamic range (SFDR) at the same bias is measured at 118 dB/spl middot/Hz/sup 2/3/. The single-octave SFDR at the third-order null bias is 132 dB/spl middot/Hz/sup 4/5/.     

Fabrication of large-core 1/spl times/16 optical power splitters in polymers using hot-embossing process

Large-core (42 /spl times/43 /spl mu/m) 1/spl times/16 optical power splitters in polymers have been fabricated. Y-branch waveguide structures with and without offsets in the arc-bending regions were designed by the beam propagation method software and molded by a silicon-mold master using a hot-embossing process. The optical power splitters were produced by epoxy core filling and ultraviolet curing processes. The average insertion losses at a wavelength of 850 nm were measured to be 19.8 dB with offset and 17.1 dB without offset, respectively. The maximum uniformities were 3.3 dB with offset and 3.9 dB without offset, respectively.     

Low Rayleigh scatteringP2O5-F-SiO2 glasses

The Rayleigh scattering and infrared absorption losses of P₂ O₅-F-doped silica glass, which is a candidate material for ultra-low-loss optical fiber, were investigated experimentally. The Rayleigh scattering loss of 8.5 wt.% P₂O₅ and 0.3 wt.% F-doped SiO₂ glass is found to be 0.8 times that of pure silica glass. It is also found that the infrared absorption property of P₂O₅-F-SiO₂ glass is almost the same as that of pure silica glass. The minimum loss for the proposed composition is estimated to be 0.11 dB/km at 1.55 μm wavelength, and 0.21 dB/km at 1.3 μm wavelength     

A monolithic CMOS 2368/spl plusmn/30 MHz transformer based Q-enhanced series-C coupled resonator bandpass filter

A three-pole 0.1 dB ripple Chebyshev series-C coupled resonator bandpass filter with transformer-based Q-enhancement is presented. This Q-enhancement technique compensates resonator loss and produces a flat passband response with low insertion loss. The compensation scheme uses frequency-dependent negative resistance to compensate frequency-dependent inductor losses, avoiding passband distortion, which is a problem with cross-coupled negative resistance circuits. Fabricated in 0.18 /spl mu/m CMOS, the measured filter center frequency is 2368 MHz with a 60 MHz (3 dB) bandwidth, including probe pad and connecting trace parasitic losses. The filter draws 5.84 mA at 1.5 V, and the die area is 1.5 mm/spl times/1.5 mm.     

Optical filtering to reduce chirping influence in LD wavelength conversion

The use of an optical filter to reduce chirping influence in LD wavelength conversion is demonstrated. A part of broadened spectrum of wavelength-converted light is eliminated by a narrow-band optical filter, and sensitivity degradation due to frequency chirping is reduced as a result. In an experiment using a fiber Fabry-Perot filter, the sensitivity was improved by about 1.5 dB in 1.55-/spl mu/m transmissions with normal dispersion fibers when an LD converter was biased at two times the threshold current.     

First InP-based reconfigurable integrated add-drop multiplexer

A four-channel reconfigurable integrated add-drop multiplexer on InP-substrate is reported. The device consists of a 5/spl times/5 PHASAR demultiplexer integrated with Mach-Zehnder interferometer electrooptical switches. Total device size is 3/spl times/6 mm/sup 2/. All routing configurations of four wavelengths have been demonstrated. Crosstalk values are better than -20 dB. On-chip loss for the dropped or added signals and for the signals coupled from the input to the output port are lower than 7 and 11 dB, respectively.