1/spl times/4 optical switch based on transversal filter configuration with constant power consumption

An optical switch based on a transversal filter configuration is demonstrated. The switch consists of cascaded 3 dB optical power splitters and a phase shifter array. By using a silica-based planar lightwave circuit, a 1/spl times/4 optical switch was realised. A characteristic of the switch is that its power consumption is constant regardless of the output selection.     

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 2 /spl times/ 8 power splitters in silica-on-silicon by the direct UV writing technique

In this letter, we present the first demonstration of 2 /spl times/ 8 power splitters made in silica-on-silicon by direct ultraviolet (UV) writing. The fabricated components are compact and exhibit good performance in terms of loss, uniformity, and bandwidth, showing that direct UV writing can become a competitive technology for fabrication of low-cost integrated optical devices.     

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.     

Hybrid WDM/TDM-PON with wavelength-selection-free transmitters

A hybrid wavelength-division-multiplexed/time-division-multiplexed passive optical network serving 128 subscribers with wavelength-selection-free transmitters is presented by cascading 1/spl times/16 arrayed-waveguide gratings (AWGs) and 1/spl times/8 splitters. The wavelength-selection-free transmitter is an uncooled Fabry-Pe/spl acute/rot laser diode (FP-LD) wavelength-locked to an externally injected narrow-band amplified spontaneous emission (ASE). Bit-error rates better than 10/sup -9/ over temperature ranging from 0 to 60/spl deg/C are achieved in all 16 wavelength channels using a single FP-LD with an ASE injection of about -15 and -2 dBm in 622-Mb/s upstream and 1.25-Gb/s downstream transmissions over a 10-km feeder fiber, respectively. It is also reported that the ASE injection does not exert penalty upon burst-mode operations of the FP-LDs in the upstream.     

A 256-element CMOS imaging receiver for free-space optical communication

This paper describes a CMOS imaging receiver for free-space optical (FSO) communication. The die contains 256 optical receive channels with -47 dBm optical sensitivity and 30 dB optical dynamic range at 500 kb/s/channel while consuming 67 mW. Received signals are amplified by digitally self-calibrated open-loop amplifiers and digitized before clock and data recovery. The sampled data also provide inputs for digital automatic gain and offset control loops closed around the analog amplifier chain to compensate for signal variations due to atmospheric turbulence and daylight interference. Gain control logic can adapt to incident signals over the 30 dB dynamic range within 28 bit periods. Low-power logic design and analog circuit techniques are used to minimize digital crosstalk to single-ended photodetectors referenced to a bulk substrate. Local arbitration circuitry at each channel forms an intrachip data passing network to multiplex received data words from the 16 /spl times/ 16 array onto a common off-chip bus. The 1.6 M transistor mixed-signal die fabricated in a 0.25 /spl mu/m CMOS process measures 6.5/spl times/6.5 mm/sup 2/. Reception at 500 kb/s through a 1.5 km atmospheric channel is demonstrated with 3 mW optical transmit power during nighttime and daylight hours.     

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.     

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.     

A 10-Gb/s receiver with series equalizer and on-chip ISI monitor in 0.11-/spl mu/m CMOS

A 10-Gb/s receiver is presented that consists of an equalizer, an intersymbol interference (ISI) monitor, and a clock and data recovery (CDR) unit. The equalizer uses the Cherry-Hooper topology to achieve high-bandwidth with small area and low power consumption, without using on-chip inductors. The ISI monitor measures the channel response including the wire and the equalizer on the fly by calculating the correlation between the error in the input signal and the past decision data. A switched capacitor correlator enables a compact and low power implementation of the ISI monitor. The receiver test chip was fabricated by using a standard 0.11-/spl mu/m CMOS technology. The receiver active area is 0.8 mm/sup 2/ and it consumes 133 mW with a 1.2-V power supply. The equalizer compensates for high-frequency losses ranging from 0 dB to 20 dB with a bit error rate of less than 10/sup -12/. The areas and power consumptions are 47 /spl mu/m /spl times/ 85 /spl mu/m and 13.2 mW for the equalizer, and 145 /spl mu/m /spl times/ 80 /spl mu/m and 10 mW for the ISI monitor.     

玻璃基多模波导光功分器的研制

利用Ag+-Na+电场辅助玻璃基离子交换技术制作了低损耗的掩埋多模波导,并在此基础上研制了多模波导光功分器.测试分析了多模波导和光功分器的损耗和偏心率特性.所研制的多模直波导传输损耗小于0.1dB/cm,所制作的1×2的多模波导光功分器附加损耗小于1.3 dB.     

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.     

Low-loss fiber-matched low-temperature PECVD waveguides with small-core dimensions for optical communication systems

Plasma-enhanced chemical vapor deposition (PECVD) offers a simple way of fabricating (doped) silica layers on silicon. A new design of the waveguide core allows low-loss fiber matched waveguides with low birefringence without high-temperature annealing. The increased loss of doped plasma deposited silica due to hydrogen incorporation is overcome by reducing the core dimensions and increasing the refractive index contrast. The waveguides can easily be fabricated using standard PECVD technologies and resist masked reactive ion etching (RIE) etching. Integrated optical devices such as 1/spl times/8 power splitters, 1300/1550-nm wavelength multiplexers and thermooptical switches were successfully fabricated and tested.     

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.     

Multimode optical demultiplexer for DWDM with liquid crystal enabled functionalities

We have developed a liquid-crystal-based multimode optical demultiplexer (DEMUX) with additional functionalities such as switching and power equalization. Demultiplexing 16-channel 100-GHz-spaced signals into a 62.5-/spl mu/m multimode-fiber array is demonstrated. The central wavelength of each channel is designed according to the International Telecommunication Union grid. Adjacent channel crosstalk is less than -30 dB. The average 1and 3-dB passbands of the DEMUX are 12.5 and 22.5 GHz, respectively. A maximum extinction ratio of 16.2 dB is achieved. Different channels can be switched with rise and fall times of /spl sim/10 and /spl sim/70 ms, respectively. The outputs of the channels are equalized to -65 dBm. The variation between different channels reduced from /spl sim/10 dB to less than 0.5 dB.     

Evanescently coupled photodiodes integrating a double-stage taper for 40-Gb/s applications-compared performance with side-illuminated photodiodes

The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes.     

Transmission performance analysis of 8/spl times/10 Gb/s WDM signals using cascaded SOAs due to signal wavelength displacement

We have analyzed the transmission performance of 8/spl times/10 Gb/s wavelength division multiplexing (WDM) signals due to crosstalk in cascaded conventional semiconductor optical amplifiers (SOAs). Using two different methods, the crosstalk over the whole gain bandwidth in SOAs is calculated to be 2-5 dB lower for the positive detuning. Then, transmission performance of 8/spl times/10 Gb/s WDM signals up to 6/spl times/40 km span in terms of receiver sensitivity is estimated over various transmission distances using cascaded SOAs for the positive signal wavelength displacement of 30, 40, and 50 nm. Especially for 50 nm detuning, transmission performances with and without using a reservoir channel are similar to each other. Our results suggest that SOAs can be used as an optical amplifier for displacement larger than 50 nm without using the reservoir channel.     

Self-heating and trapping effects on the RF performance of GaN MESFETs

RF power performances of GaN MESFETs incorporating self-heating and trapping effects are reported. A physics-based large-signal model is used, which includes temperature dependences of transport and trapping parameters. Current collapse and dc-to-RF dispersion of output resistance and transconductance due to traps have been accounted for in the formulation. Calculated dc and pulsed I-V characteristics are in excellent agreement with the measured data. At 2 GHz, calculated maximum output power of a 0.3 /spl mu/m/spl times/100 /spl mu/m GaN MESFET is 22.8 dBm at the power gain of 6.1 dB and power-added efficiency of 28.5% are in excellent agreement with the corresponding measured values of 23 dBm, 5.8 dB, and 27.5%, respectively. Better thermal stability is observed for longer gate-length devices due to lower dissipation power density. At 2 GHz, gain compressions due to self-heating are 2.2, 1.9, and 0.75 dB for 0.30 /spl mu/m/spl times/100 /spl mu/m, 0.50 /spl mu/m/spl times/100 /spl mu/m, and 0.75 /spl mu/m/spl times/100 /spl mu/m GaN MESFETs, respectively. Significant increase in gain compression due to thermal effects is reported at elevated frequencies. At 2-GHz and 10-dBm output power, calculated third-order intermodulations (IM3s) of 0.30 /spl mu/m/spl times/100 /spl mu/m, 0.50 /spl mu/m/spl times/100 /spl mu/m, and 0.75 /spl mu/m/spl times/100 /spl mu/m GaN MESFETs are -61, -54, and - 45 dBc, respectively. For the same devices, the IM3 increases by 9, 6, and 3 dBc due to self-heating effects, respectively. Due to self-heating effects, the output referred third-order intercept point decreases by 4 dBm in a 0.30 /spl mu/m/spl times/100 /spl mu/m device.     

A complete single-chip GPS receiver with 1.6-V 24-mW radio in 0.18-/spl mu/m CMOS

A compact ultra-broadband MMIC-compatible uniplanar balun has been developed using offset air-gap coupler. The offset air-gap coupler presents tight coupling and low conductor loss, and thus allows the balun to show low loss at mm-wave frequencies. The measured insertion loss was less than 2 dB from 26 to 55 GHz, and amplitude and phase imbalance was less than /spl plusmn/1dB and 5/spl deg/, respectively over a wide frequency range from 27 to 69 GHz.     

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.