Tomofumi Kise

Recent advances in DFB lasers for ultradense WDM applications

State-of-the-art distributed feedback (DFB) laser modules integrated with a wavelength monitor are presented that provide excellent wavelength stability. By adopting unique and compact configuration, wavelength deviations of as small as a few picometers have been achieved. The laser modules are improved also in the scope of high power, high reliability, and wavelength tunability. Reliability test results of the DFB laser diodes and modules confirm a sufficiently long lifetime of more than 25 years and a small wavelength drift of less than /spl plusmn/3 pm. The developed laser modules are fully applicable to ultradense wavelength-division multiplexing applications with the current narrowest channel spacing of 25 GHz.

Various low group velocity effects in photonic crystal line defect waveguides and their demonstration by laser oscillation

We investigated propagating modes in a two-dimensional photonic crystal slab waveguide with a line defect narrower than a single line missing hole structure from the low group velocity point of view. These modes showed low group velocities not due to the conventional distributed feedback (DFB) between a forward and a backward mode with the same lateral field distribution, but due to a DFB between modes with different lateral field distribution or property of a start point of a photonic-band-gap-guided mode. These low group velocities of over 40 were demonstrated as a Fabry-Perot lasing oscillation due to gain enhancement.

Reduced linewidth re-broadening by suppressing longitudinal spatial hole burning in high-power 1.55-/spl mu/m continuous-wave distributed-feedback (CW-DFB) laser diodes

For the first time, the impact of longitudinal photon density distribution and longitudinal carrier density distribution on the spectral linewidth re-broadening effect in single-electrode 1.55-/spl mu/m distributed feedback (DFB) laser diodes (LDs) is investigated experimentally in details. By optimizing the front-to-rear facet power ratio, the nonuniformity of the photon density distribution along the laser cavity is reduced, hence reducing the degree of longitudinal spatial hole burning (SHB). Using this optimized value of front-to-rear facet power ratio, the degree of longitudinal SHB can be further reduced through reduction of the nonuniformity of the longitudinal carrier density distribution by increasing the cavity length. As a result, the local stimulated emission is reduced, hence reducing linewidth re-broadening caused by longitudinal SHB. The outcomes of this analysis is being used fruitfully to design high-power 1.55-/spl mu/m DFB LDs exhibiting very narrow spectral linewidth of approximately 1.3 MHz at an output power of 175 mW under continuous-wave operation.

A Record 1-km MMF NRZ 25.78-Gb/s Error-Free Link Using a 1060-nm DIC VCSEL

We report successful achievement of a record long distance error-free transmission of 1000-m 50-μm-core multimode fiber (MMF) in a non-return-to-zero 25.78-Gb/s modulated vertical cavity surface emitting laser-based optical link using four-channel miniature parallel-optical modules. The optical power is centralized within the core of MMF by an active alignment assembly. The restricted launch condition gives a very high effective modal bandwidth (EMB) of >9 GHz · km based on the calculations and the required performance data specified in TIA-FOTP-220. An EMB of 11.5 GHz · km provides a very good agreement between the calculated and measured power penalty characteristics. Such a long distance low-cost MMF link, operating at 1060-nm wavelength is potentially an alternative solution to PSM4.

50Gbit/s PAM-4 MMF Transmission Using 1060nm VCSELs with Reach beyond 200m

We experimentally demonstrate error-free transmission of 50Gbit/s PAM-4 signals over OM3 and prototype wideband fiber using 1060nm VCSELs. FEC-conformed performance is demonstrated over 200m. An analytic model allows identification of penalties and demonstrates negligible MPN.

VCSEL-based parallel-optical modules for >100 Gb/s applications

We introduce solder reflow-capable high-density parallel-optical modules for >100 Gb/s optical interconnects. Polymer-waveguide-coupled parallel-optical modules are also introduced with a unique mounting technology. 1060-nm 28-Gb/s InGaAs/GaAs VCSEL realizes a good signal quality at high temperature and error free for MMF transmission beyond 500m.

1060-nm 28-Gb/s

To reduce the power consumption of 4-channel 28-Gb/s miniature optical modules, a 4-channel double intra-cavity 1060-nm InGaAs/GaAs quantum-well vertical-cavity surface-emitting laser (VCSEL) array with 5-μm-wide apertures, a high differential gain, and a low temperature-insensitive differential resistance in conjunction with a specially optimized thermo-electric cooler heat sink for a reduced thermal resistance are used. Most important is the excellent resistance compatibility between the VCSEL and a low-power SiGe BiCMOS driver IC. Consequently, a 4-channel 28-Gb/s NRZ PRBS 231 - 1 link operation at a bit error rate of 10-12 for an operational case temperature ranging from 25 °C to 70 °C was achieved at an unprecedentedly low VCSEL bias current of only 4 mA.

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We report the design and transmission characteristics of clock-data-recovery (CDR)-integrated 28-Gb/s × 4-channel parallel-optical modules for QSFP28 AOCs. The module keeps the same package size with the 28-Gb/s × 4-channel module that we reported in a previous work. The CDR circuitry was integrated to the new module. Owing to the CDR functionality, we achieved a link total jitter margin of >0.4 U.I. when operating at a bit stream of 28-Gb/s, 231-1 PRBS. A degraded electrical signal at the TX input can be compensated by the CDR circuitry to fully meet the specification of CEI-28G-VSR, where the total jitter margin was improved from 0.06 U.I. to 0.42 U.I. successfully together with remarkably low power dissipation of 390 mW/lane.

-Channel Modules Operated Over the Case Temperature Range

We report a solderable 4-channel VCSEL-based optical transceiver module perfect for high-volume production of QSFP AOCs. The 4-channel module can be simply mounted on a PCB together with other electronics components through a solder reflow process. We fabricated a PCBA in compliance with the standard of QSFP edge connector. The PCBA has an MCU written with a firmware included with a look-up table to control the optical module over the operating temperate range. Integrating the PCB assembly into a die-cast housing, we fabricated fully engineered QSFP AOC. As we tested a BER characteristic for 14-Gb/s ×4-channel operation, the QSFP AOC has a total jitter margin of 0.5 U.I., and achieve a BER of <;10-15.

CDR-integrated Sn-Ag-Cu-solder reflow-capable miniature 28-Gb/s × 4-channel optical modules

We demonstrate an error free 28-Gb/s × 4-channel parallel-optical link using Sn-Ag-Cu solder reflow-capable miniature 1060-nm VCSEL-based optical modules. As an alternative solution to PSM4, we achieved error free transmission in 50-micrometer-core MMF beyond 500 m, owing to a low chromatic dispersion at 1060-nm, when the modules are operated at a bit stream of 28-Gb/s 231-1 PRBS.