Y. Suzaki

Multi-channel modulation in a DWDM monolithic photonic integrated circuit

We present a multi-channel modulation circuit monolithically integrated with one 25-GHz-spacing AWG for both MUX and DEMUX and eight channels of SOAs and EAMs. The circuit can generate individual optical signals for each DWDM channel with a high extinction ratio of >20 dB and loss compensation. The circuit size can be reduced to 15 /spl times/ 7 mm/sup 2/.

Optical spot-size converters for low-loss coupling between fibers and optoelectronic semiconductor devices

Structures of spot size converters that allow low loss and easy coupling between an optical semiconductor device and a fiber are proposed and designed theoretically. These spot-size converters have a tapered small core for expanding the mode field. They also have a double cladding region which consists of an n/sup +/-doped InP substrate as the outer cladding and a p-doped or nondoped InP layer as the inner cladding with a ridge structure. This double cladding utilizes the plasma effect of a carrier which makes the refractive index of highly doped n-InP lower than that of p-doped or nondoped InP. The double-cladding structure can tightly confine an expanded mode field in the inner cladding, and results in low radiation loss at the tapered waveguide, in addition, this structure reforms the mode field shape into a Gaussian-like shape and achieves a low loss coupling of less than 1 dB with a large misalignment tolerance for fiber coupling. These spot-size converters are easily fabricated and applicable to all types of optical semiconductor devices.

Lossless electroabsorption modulator monolithically integrated with a semiconductor optical amplifier and a passive waveguide

We have developed a monolithic integrated device consisting of an electroabsorption modulator and a semiconductor optical amplifier (SOA) connected by a deep-ridge passive waveguide by means of butt-joint selective area growth. Lossless operation with a high extinction ratio of 32 dB and clear eye opening at 10 Gb/s are successfully achieved. We confirm that the optical injection should be from the SOA side of the device to obtain a wide error-free range of incident optical power from -20 to +10 dBm. Our device could lead to richly functional photonic integrated circuits comprising arrayed waveguide gratings (AWGs) for advanced wavelength-division-multiplexing networks, since the passive waveguide has the same structure as AWGs.

Low Chirp Operation of 40 Gbit/s Electroabsorption Modulator Integrated DFB Laser Module With Low Driving Voltage

We clarified experimentally that an EA-DFB laser in which the EAM and DFB parts are coupled with a passive waveguide provides a large bandwidth, even when a large reverse bias is applied to the EAM. This allows the chip to operate in a negative-chirp condition. We fabricated an EA-DFB module terminated with a 50 Omega resistor through a dc-block capacitor to suppress the increase in dc current as the reverse bias increases. A module equipped with our new EA-DFB chip successfully transmitted data over a distance of 3 km at a rate of 40 Gbit/s and at a driving voltage as low as 2 V.

Monolithically integrated eight-channel WDM modulator with narrow channel spacing and high throughput

We demonstrate an eight-channel wavelength division multiplexing (WDM) modulator module that monolithically integrates arrayed waveguide gratings and semiconductor optical amplifiers and electroabsorption optical modulators arrays. The compact module can generate individual optical signals for each WDM channel with low optical and electrical crosstalk. We show two configurations for the narrow channel spacing of 25 GHz and high throughput of beyond 80 Gb/s. Combining this WDM modulator with a multi-wavelength light source is a promising approach to creating a compact WDM optical transmitter.

Laser diodes integrated with butt-jointed spotsize converter fabricated on 2-in wafer

Laser diodes integrated with spotsize converters by butt-joint technology combined with selective area metal organic vapor phase epitaxial (MOVPE) growth have been successfully fabricated. Satisfactory uniformity, reproducibility (>99%) and tolerance for low threshold current, a narrow emitted beam, and low optical coupling loss to fiber (<-2.4 dB) are obtained by using 2-in full wafer fabrication technology in the experimental fabrication. To investigate the tolerance in fabrication, the characteristic dependence on the variation of the wet etching time just before the butt-joint MOVPE growth and also on the mesa stripe width are investigated. A wide tolerance for these fabrication parameters is confirmed. The results indicate that the butt-joint technology is a useful and reliable process for realizing spotsize converters of the present type and also suggest that the technology is widely applicable to various photonic integrated circuits.

Eight-channel simultaneous wavelength conversion from equal to unequal channel spacing

Eight-channel simultaneous wavelength conversion from equal to unequal wavelength-division-multiplexing (WDM) channel spacing is successfully demonstrated using two arrayed-waveguide-gratings (AWGs) and cross-gain modulation (XGM) in a spot-size converter-integrated semiconductor optical amplifier array on a planar-lightwave-circuit platform. The input AWG concurrently demultiplexed both the equal-spaced WDM signal and unequal-spaced pump lights to couple a pair comprising a signal and a pump for the XGM. Only a small power penalty of less than 0.5 dB was observed for all eight channels. The receiver sensitivity at 2.5 Gb/s was -33 dBm for all eight channels.

Improvement of spectrum characteristics in spot-size converter integrated lasers with tilted butt joint portion

Summary form only given. A spot-size converter integrated MQW laser with a tilted butt joint was fabricated to reduce reflection from the joint. It produced no degradation in bit error rate performance and repeatedly provided low threshold current and low coupling loss to the cleaved fiber in 2 inch wafer process.

Design and dynamic properties of an optical transceiver diode with a bulk detection layer

We clarify the impact of a bulk detection layer in an optical transceiver diode for low-cost time compression multiplexing (TCM) transmission systems. By optimizing the detection layer for both transmitter and receiver operations, we obtain temperature- and wavelength-insensitive responsivity, and the power penalty of sensitivity is within 0.55 dB over a wide-wavelength range in the receiver mode. The pulsation due to the detection layer is also effectively suppressed in the transmitter mode. We demonstrate a switching operation for 156-Mb/s nonreturn-to-zero burst signals, which is indispensable for TCM transmission systems.

Self-routing demonstration of a 320-Gbit/s packet switch prototype using wavelength routing techniques

Summary form only given.The current rapid growth of data traffic, such as Internet traffic, and the continuing development of WDM techniques show that large-capacity WDM transmission and intelligent IP routers are expected to be effectively combined. And thus large-scale packet switching nodes will have to have a total throughput of over 1 Tbit/s. A l0-Gbit/s and 32-wavelength-channel photonic packet switch has been developed. Practical electrical control circuits including 10-Gbit/s serial-I/O LSIs for packet-based self-routing operation were implemented into it as well as optical WDM circuits. Self-routing operation was successfully demonstrated.