Search

An endless, reset-free polarization controller implemented with planar lightwave circuits using phase shifters for tuning is proposed and demonstrated. By avoiding the need for tunable polarization mode converters, simple fabrication processes and a large range of material systems can be used, since neither the electrooptic effect nor a rotatable birefringence axis are necessary for device operation. The proof of concept is demonstrated by implementing the equivalent of a rotating waveplate using Ge-doped silica-on-silicon waveguides and thermooptic phase shifters. The polarization controller is shown to have excellent tolerance to fabrication variations. Fast thermooptic control (on the order of 10 kHz) is achieved using high-index-contrast (4%) waveguides.

We discuss options for upgrading coarse wavelength-division multiplexed (CWDM) optical access links over standard single-mode fiber (SSMF) by increasing per-channel data rates from 2.5 to 10 Gb/s. We identify electronic equalization and forward error correction (FEC) as the enabling technologies to overcome the dispersion limit of SSMF. In addition, we show how FEC enhances the tolerance to in-band crosstalk, and paves the way toward fully bidirectional CWDM transmission. Due to the lack of CWDM sources rated for 10-Gb/s operation, we demonstrate full-spectrum (1310 to 1610 nm) 10-Gb/s CWDM transmission over standard-dispersion fiber using uncooled, directly modulated lasers specified for 2.5 Gb/s. All 16 CWDM channels could be transmitted over more than 40 km, yielding a capacity-times-distance product of 6.4 Tb/s/km. The longest transmission distance (80 km) was achieved at 1610 nm, equivalent to 1600 ps/nm of chromatic dispersion.

We integrated a wavelength-selective cross-connect, de-interleaver, interleaver, power combiner, and variable attenuators on one silica waveguide chip and a band demultiplexer, band multiplexer, and optical monitor on another. These two chips are used to create an eight-channel add-drop node that is expandable up to 80 channels with minimal traffic interruption by adding more of these chips.

Highly versatile building blocks for polarization-mode dispersion (PMD) emulation and compensation are demonstrated using tunable all-pass filters fabricated in 4%-index-contrast planar waveguides. While the all-pass filters can approximate any phase response, the complexity in setting the individual filter parameters is minimized by restricting the all-pass filter responses to realize a range of differential delays, dispersion, and dispersion slope. A single section can approximate first-order or a higher-order PMD term or emulate chromatic or higher-order dispersion. A differential group delay (DGD) tuning range over 100 ps is demonstrated for 10 Gb/s and 25 ps for 40 Gb/s data. Second-order PMD with a tuning range of 255 ps/sup 2/ and third-order PMD with a range of 2430 ps/sup 3/ are also demonstrated. The larger index contrast required for the ring-resonator-based all-pass filters is advantageous in reducing the thermooptic response time to achieve polarization rotation speeds on the order of 0.1 /spl mu/s/degree. The device is interferometrically stable and compact in size. It can be fully integrated, scaled to many sections, and can implement a variety of PMD synthesis and statistical-emulation approaches.

A new reflective configuration for a monolithically integrated channel selector with power monitor is proposed. One star coupler, one arrayed waveguide grating, and a minimum number of semiconductor optical amplifier (SOA) gates are used to achieve loss-free transmission. A 32-channel device controlled by only 12 SOA gates is realized in InP. Low on-chip losses result in strongly reduced bias currents and an improved signal to noise ratio compared to previously demonstrated devices. The use of SOAs allows for switching on a nanosecond time scale.

This paper demonstrates a nine-channel waveguide grating router-based laser with low (18-22 mA) thresholds, which we believe to be a record for a monolithically integrated multiwavelength laser with a 1.1-cm long cavity and a single nondistributed amplifier. This result was achieved through a combination of techniques including reduced intracavity loss, improved router design and optimal active/passive transitions.

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 /spl mu/s 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.

This paper characterizes a ten-channel waveguide grating router multifrequency laser (MFL) with 200-GHz channel spacing coupled to a 2.5-Gb/s electroabsorption modulator on a separate chip. We show theoretically and experimentally that in long-cavity semiconductor lasers such as the MFL, light reflected back into the laser perturbs the device wavelength a negligible amount compared to the inherent modulator dynamic chirp but can cause multimode lasing. However, if the ratio of the net external reflectivity to the laser facet reflectivity is kept below approximately 1/(4/spl alpha//sup 2/+1) where /spl alpha/ is the linewidth enhancement parameter in the laser, the lasing spectrum is immune to the back-reflected light. We also show that placing a simple "isolator" that only has to rotate the polarization of the back-reflected light rather than provide full isolation can easily provide the immunity.

Uncooled 2.5-Gb/s directly modulated lasers are used to demonstrate a coarse wavelength-division-multiplexed (CWDM) transmission capacity of 160 Gb/s. All 16 CWDM channels, modulated at 10 Gb/s, are simultaneously transmitted over 40 km of uncompensated low-water-peak nonzero dispersion fiber. Operation with bit-error ratio BER less than 1 E-9 is demonstrated for all 16 channels from room temperature to at least 65 C.

A high-speed low-drive-voltage travelling wave electrodes InGaAsP-InP phase modulator operated at 1.55 /spl mu/m is demonstrated. The modulator is fabricated using a multiple quantum-well optical waveguide with an on chip integrated termination resistor. A small signal bandwidth of 35 GHz and a V/spl pi/ of 1.8 V has been demonstrated.

We demonstrate significant improvement in the measured bit-error rates of 40-Gb/s signals distorted after passing through a saturated semiconductor optical amplifier (SOA) by using a simple colorless general optical equalizer. The optical equalizer reduces the overshoots arising from the nonlinear gain dynamics of the SOA and improves the opening of the eye. We study the improvement in receiver sensitivity by using the equalizer while varying the optical power and wavelength at the input of the SOA.

A 16-channel 100-GHz-spacing wavelength selective cross connect is demonstrated using a combination of planar waveguides and MEMS piston-mirrors. Interswitch crosstalk is eliminated and switching speed is an order of magnitude faster than typical thermooptic switches. The power consumption is smaller than one microwatt per switch. An extinction ratio of 20 dB and an insertion loss of 10.6 dB are demonstrated.

A novel technique for monitoring the alignment status between the pulse carver and data modulator for return-to-zero differential phase-shift keying systems is proposed and demonstrated. The proposed technique utilizes a polarization-maintaining fiber, polarizer, and power meter. Both the simulation and measurement results show that the proposed technique can monitor the bit-error-rate degradation caused by timing misalignment between the pulse carver and data modulator.

We demonstrate that a simple general optical equalizer permits the generation of 42.7-Gb/s nonreturn-to-zero data from an 8-GHz bandwidth LiNbO/sub 3/ modulator. The sensitivity at 10/sup -9/ bit-error ratio is only 1 dB poorer than using a 36-GHz bandwith modulator. Since the equalizer can act on many channels simultaneously and be used in a set-and-forget mode, we can potentially reduce the cost of 40-Gb/s transmitters.

We demonstrate six-channel 160-Gb/s wavelength-division-multiplexed transmission over 20 100-km spans of nonzero-dispersion fiber, with a spectral efficiency of 0.53 b/s/Hz. We achieve this result using optical-time-division multiplexing with polarization bit interleaving and return-to-zero differential-phase-shift-keying modulation format. We also operate at 170.6 Gb/s per channel to emulate the use of forward error correction.

We demonstrate a colorless thermooptic-lens-based tunable dispersion compensator integrated with a tunable optical noise filter. The free-spectral range is 200 GHz, the tuning range is /spl plusmn/200 ps/nm, the transmissivity 3-dB bandwidth is >40 GHz, and the linear group delay bandwidth is >48 GHz.

We present a novel band demultiplexer design for planar lightwave circuits. It consists of two perfectly sampled waveguide grating routers connected by sets of equal-path-length waveguides separated on one side. Its advantages are compactness, sharp passband corners, and a lack of chromatic dispersion.

A fully packaged 40-channel 100-GHz-spacing full-coupler-type synchronized-gratings multiplexer with a 1-dB bandwidth >57 GHz, total adjacent crosstalk /spl plusmn/35 GHz around the ITU grid

We report the first transmission of copolarized 40-Gb/s channels with 0.8-b/s/Hz spectral efficiency. We transmit 25 channels over 1200 km of nonzero-dispersion fiber (1600 km with adjacent channels orthogonally polarized). This result was obtained using differential phase-shift keying, and without forward error correction.

A record sensitivity of -36.2 dBm at 1552.5-nm wavelength (45 photons/bit) is reported for an optically preamplified receiver operating at 42.7 Gb/s. The transmission format is return-to-zero differential phase-shift keying. The receiver employs a delay-interferometer demodulator followed by balanced-photodiode detection and electronic demultiplexing to 10.7 Gb/s.

We present an efficient 2 /spl times/ 2 wavelength-selective cross connect that is serviceable without interrupting traffic. It can handle over a hundred channels in a compact fashion by operating on them in sets. The 50-GHz-spaced passbands are flat-topped with no gaps between them, and so it has high cascadability and can exhibit variable-bandwidth switching. It also can multicast. Index Terms-Cross connect, glass materials/devices, optical phase shifters, waveguide filters, wavelength-division multiplexing.

We demonstrate a low-loss 16-band dynamic gain equalization filter consisting of two perfectly sampled waveguide grating routers (WGRs) and an array of thermooptic attenuators. This integrated silica waveguide filter has

We present a compact design for flattening the passband of a waveguide grating router theoretically without excess loss or chromatic dispersion. We demonstrate its use in a 64-wavelength-channel blocker/multiplexer.

The authors report a simple technique to synchronize solid etalons which provides identical sets of equally spaced absolute reference frequencies. To demonstrate the principle, 1-mm-thick fused silica etalons were synchronized to have identical sets of resonant frequencies at 195.579+or-n*0.1034 THz, where n is any integer. These references were temperature-insensitive with the aid of a temperature control loop. These synchronized etalons could be used for standardizing the wavelengths of transmitter lasers in large-scale WDM wavelength division multiplexed networks. >

We present a planar 40-wavelength 100-GHz spacing channel-dropping filter with wide in-to-through stopbands and low in-to-drop crosstalk, yet highly cascadable in-to-through passbands without significant excess loss or large physical size.

This letter presents an integrated multi/demultiplexer that can dynamically and independently control the curvature, tilt, and attenuation of its passband shapes, in order to reduce the signal distortion caused by other filters in the network. 40 Gb/s performance is demonstrated.

We present an arrayed waveguide dynamic gain equalization filter with less than 4.5-dB insertion loss and greater than 14-dB dynamic range over the C-band resulting from three improvements: a circulator and polarization splitter combined into one, used to make the device polarization insensitive; segmentation in the star coupler transition regions; and an exponential control wavelength distribution.

Narrowband optical filters were made by direct deposition of thin films of TiO/sub 2/ and SiO/sub 2/ on the ends of optical fibers. Single-cavity etalons with bandwidths of 1.1 nm, insertion loss of 1 dB, and 2.25 nm, insertion loss of 0.5 dB, were made. It is necessary to use fibers with mode fields larger than standard single mode fiber. Thermal expansion was used to diffuse the core dopant and produce tapered-core fibers with mode-field diameters of 22 mu m. >

We describe a 40-channel X 9.953 Gbit/s dense wavelength-division multiplexed (DWDM) transmitter based on spectrum-slicing of supercontinuum light generated from an electroabsorption-modulated laser (EML). Error-free transmission of all channels over 544 km of standard fiber is demonstrated.

We demonstrate a wavelength equalizer in planar silica waveguides that can automatically control individual channel powers in a 40-channel 100-GHz-channel-spacing wavelength-division multiplexed system, yet gives no distortion to channels that already have the same power as their neighbors. It has

We present in 40-wavelength, 100-GHz channel spacing, programmable, planar add-drop filter that has flattened passbands without excess loss. For TE polarized light, the insertion loss is 9-11 dB for the through channels, and the dropping extinction ratio is /spl ges/33 dB.

We present a tunable laser based on an N/sub 1//spl times/N/sub 2/ chirped waveguide grating router that has N/sub 1/N/sub 2/ wavelengths, accessible in a digitally rapid manner, and only N/sub 1/+N/sub 2/+1 semiconductor optical amplifiers. By using chirp, the free-spectral range of the router can be significantly less than the channel span. The version demonstrated here has N/sub 1/=5, N/sub 2/=8, a channel spacing of 100 GHz, and the router free-spectral range is only 20 channels.

A microprocessor-controlled dynamic wavelength equalizer is presented. Th subsystem is based on an integrated optical circuit made in silica and covers a large portion of the usable region of the electromagnetic spectrum for optical fiber transmission (1530-1565 nm). The chip is connected in a software-controlled feedback loop, and with its dynamic range of /spl sim/7 dB for each channel, the system is capable of flattening the spectral response of an erbium-doped fiber amplifier to within 0.35-dB peak-to-peak. Insertion loss equals /spl sim/8 dB.

We demonstrate a ten-channel 100-GHz spacing, waveguide grating router multifrequency laser that has significantly reduced intracavity wave mixing. The mixing products for the improved design are now too small to cause significant laser fluctuations during simultaneous multichannel operation. This was accomplished by reducing the shared waveguide length to 150 /spl mu/m. We provide evidence that a significant portion of the remaining wave mixing occurs in the intracavity waveguide grating arms.

A dynamic wavelength equalizer that can control attenuation at 22 points across 35 nm of spectrum in a smooth manner is presented. It achieves low loss (4.7 dB), because it consists of a Mach-Zehnder interferometer with a wavelength-dependent element in only one arm. Additional development is needed to reduce the polarization sensitivity.

We present experimental results of an integrated 16-channel, 100-GHz-channel-spacing wavelength add-drop in silica. It consists of two interleave-chirped waveguide grating routers connected by an array of waveguides containing thermooptic phase shifters. The fully packaged device has 6.6-7.6-dB fiber-to-fiber insertion loss and a switching extinction ratio >27 dB (>33 dB for a single polarization) when used as an add-drop, It is compact, allowing for at least four such devices per 5-in-diameter wafer.

We report a high-voltage integrated optical-to-electrical power converter, or photogenerator, operating in the long-wavelength (1480-1650 nm) regime for use in fiber-optic networks. These devices deliver power at voltages in excess of 10 V, which is sufficient to operate switches, micromechanical devices, electronic controllers, optoelectronic circuits and other electrical devices. The high-voltage photogenerator enables provisioning and protection at unpowered nodes in fiber-optic networks, using only the long wavelength light present in the optical fiber as the power source. We also demonstrated its use with a MEMS optical shutter to construct a novel optical power limiter.

A reconfigurable 16-channel 100-GHz spacing wavelength-division-multiplexed drop module for use at 1550 nm was demonstrated using silicon microelectromechanical system (MEMS) optical switches and arrayed waveguide grating routers. Through-channel extinction was greater than 40 dB and average insertion loss was 21 dB, Both drop-and-retransmit 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 implemented.

For the frequency-division-multiple-access-frequency-shift-keying (FDMA-FSK) network, the FSK signal is converted to amplitude-shift-keyed (ASK) format by a tunable fiber Fabry-Perot (FFP) filter that acts simultaneously as a demodulator and demultiplexer. Frequency-tunable two-electrode distributed-feedback (DFB) laser transmitters produce distorted FSK spectra due to nonuniform FM response for modulation frequencies above approximately 200 Mb/s. The frequency-domain properties of the laser are related directly to the time-domain properties of the transmitted data stream. The critical dependence on the FFP passband width and center frequency location for undistorted signal recovery is shown. By optimizing these parameters, the data transmission rate can be increased while keeping the power penalty due to signal distortion below 1 dB. >

We present a design concept for dynamically and chromatically variable transmissivity devices for controlling channel powers in wavelength-division-multiplexed systems in which a decrease in attenuation range can be traded for a decrease in insertion loss. We demonstrate a version in InP.

A voltage-controlled moving-mirror microelectro-mechanical systems variable optical attenuator is described that has less than 1-dB fiber-to-fiber insertion loss at 1550-nm wavelength and greater than 50-dB dynamic range. The device was configured with a simple feedback circuit to operate as an optical power regulator capable of stabilizing the output power to within 0.26 dB for a 12-dB input power excursion.

We show that when more than two channels operate continuous-wave (CW) simultaneously in shared dispersive element wavelength-division-multiplexing (WDM) lasers, /spl chi//sup (3)/ in the passive shared waveguide can cause spontaneous fluctuations in frequency and power. We propose the simple cure of making the shared waveguide extremely short. We obtain a value for the nonlinear-index coefficient of our InGaAsP waveguides of +0.9/spl times/10/sup -12/ cm/sup 2//W.

An eight-wavelength fast packet switching transmitter using a waveguide-grating-router multifrequency laser and an external modulator is demonstrated. The transmitter is capable of switching in less than 2.8 ns among any of eight wavelengths precisely spaced by 199.8 GHz with standard deviation of 1.0 GHz.

We demonstrate a 2 line/spl times/2 line, 6 channel/spl times/200 GHz spacing, wavelength-division multiplexing (WDM) cross connect in InP consisting of two interleave chirped waveguide grating routers connected by a series of waveguides with current-controlled phase shifters. Employing a simple fabrication process, we achieved >21-dB extinction ratio, 10-12-dB on-chip loss, and switching currents

A 12-channel wavelength division multiplexed (WDM) passive optical network (PON) at 155 Mb/s with 63 km of standard single-mode fiber (SMF) was demonstrated under simulated outside plant temperature conditions. A multifrequency laser (MFL) was used as the transmitter and a waveguide grating router (WGR) as the demultiplexer. A 20/spl deg/C/h temperature change of the WGR could be tracked by changing the MFL temperature and resulted in a power penalty in the detected bit-error rate (BER) of less than 0.75 dB. A scheme to increase the tracking sensitivity by multiple WGR passes is demonstrated.

A polarization-insensitive InP-based p-i-n multiple-quantum-well switch is demonstrated for the first time. Polarization-insensitive switching and loss are achieved. Crosstalk and loss measurements across a wavelength range of 20 nm centered at 1.55 /spl mu/m are reported. A crosstalk of better than -13 dB is achieved for both TE and TM polarizations across the 1.54-1.56-/spl mu/m wavelength range with a switching voltage of -7 V. A low on-chip loss of less than 3 dB is achieved for both TE and TM across the above wavelength range, with a compact switch structure which is 3 mm long.

We present a 8/spl times/200 GHz wavelength selectable laser that has inherent wavelength and single-longitudinal-mode stability. The wavelength stabilization is accomplished by the long cavity and passive intracavity chirped waveguide grating router, and the single-mode stabilization is accomplished by gain nonlinearities, aided by minimization of cavity length and router passband width.

We demonstrate direct modulation results on a 16-channel chirped multifrequency laser without a shared amplifier, There is no optical power penalty compared to the case of a single modulated channel when all 16 channels are modulated simultaneously at 310 Mb/s, and 2 dB power penalty when they all are modulated at 622 Mb/s due to electrical crosstalk. The entire wavelength comb can be shifted by 275 GHz by changing the device temperature from 13/spl deg/C to 33/spl deg/C, while the channel-to-channel power uniformity remains better than 0.2 dB and the optical channel spacing stays exactly 200 GHz.

We present an 8/spl times/100 GHz waveguide grating multifrequency receiver in InP with low polarization sensitivity with integrated optical preamplifiers and detectors. The polarization insensitivity is achieved through a special polarization diversity scheme in which both inputs share the same waveguide grating and photodetectors. Also, we show theoretically how chirping the waveguide grating in optically preamplified receivers can improve the sensitivity.

Wavelength conversion of input signals at data rates of 622 and to 1250 Mb/s was as demonstrated using an integrated multifrequency laser having 8 channels with 1.6-nm channel spacing.