Shigeru Kanazawa

1.3-μm, 4 × 25-Gbit/s, EADFB laser array module with large-output-power and low-driving-voltage for energy-efficient 100GbE transmitter

A 1.3-μm, 4 × 25-Gbit/s, EADFB laser array module with large output power and low driving voltage is developed for 100GbE. A novel rear grating DFB laser is introduced to increase the output power of the laser while keeping the single mode lasing, which is desirable for a monolithic integration. Also, InGaAlAs-based electroabsorption modulators make very-low-driving-voltage operation possible due to their steep extinction curves. With the module, very clear 25-Gbit/s eye openings are obtained for four wavelengths with the driving voltage of only 0.5 V while securing the dynamic extinction ratio required by the system. These results indicate that the presented module is a promising candidate for energy-efficient future 100GbE transmitter.

1.3-

A 1.3- monolithically integrated light source for metro area 100-Gb/s Ethernet is developed. Four 25-Gb/s electroabsorption modulators integrated with distributed-feedback lasers and their multiplexer are monolithically integrated on one chip. A shallow ridge waveguide is used for lasers and modulators for large modulation bandwidth, and a deep ridge waveguide is used for the multiplexer region due to its low bending and radiation losses. The integration of hetero-waveguide devices enables the very small chip size of 22.6 . With the device, 100-Gb/s (4 25-Gb/s simultaneous) operation is demonstrated with the clear eye-openings, and error-free 40-km single-mode fiber transmission is achieved for the first time.

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A compact electroabsorption modulators integrated distributed feedback (EADFB) laser array module has been developed for 100-Gb/s Ethernet. Four 25-Gb/s EADFB lasers and an optical multiplexer are monolithically integrated on one chip in an area of only 2 mm × 2.6 mm. As a result, a compact 12 mm × 20 mm EADFB laser array module is achieved. A bridge-type RF circuit board is employed to transmit high-frequency, 4 × 25-Gb/s, electrical signals effectively in a narrow package and improve the electrical/optical response of the module. The module has a 3-dB frequency bandwidth of 20 GHz for the four lanes assigned in 100-Gb/s Ethernet. Furthermore, the possibility of realizing low-driving voltage operation is investigated to reduce the power consumption of the module. An error-free transmission through 10 km of single-mode fiber at 100 Gb/s with a modulation voltage of only 1 V is demonstrated.

m 4

The first ultra-compact transmitter optical sub-assembly (TOSA) has been developed for the metro-area 100 Gbit/s Ethernet (100 GbE) system. Four DFB lasers integrated with electro-absorption modulators (EADFB lasers) operated at 25.8 Gbit/s and an optical multiplexer are monolithically integrated on one chip. The chip was assembled in the compact TOSA using a three-dimensional (3D) RF circuit board supported by a spacer. The new structure provides compact and high-density interconnection with low crosstalk between RF signal lines. The TOSA is very small at just 8.0 mm × 35 mm × 6.5 mm including the receptacle and the flexible printed circuit (FPC) and could be installed in next-generation small form 100 GbE transceivers. In addition, an error-free transmission is demonstrated through 40 km of single-mode fiber at 100 Gbit/s with a modulation voltage of 2 V.

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We have achieved the 100-Gb/s/λ operation of a flip-chip interconnection 1.3-μm lumped-electrode electroabsorption modulator integrated with a distributed feedback laser module for the first time. The flip-chip interconnection provides a flatter frequency response characteristic and a higher modulation bandwidth. Clear eye opening was achieved for 103-Gb/s nonreturn to zero and equalizer-free 56-GBd 4-pulseamplitude modulation operation after a 10-km single-mode fiber transmission.

25-Gb/s Monolithically Integrated Light Source for Metro Area 100-Gb/s Ethernet

High-speed digital-to-analog converters (DACs) are essential in advanced optical transmission systems, utilizing multilevel modulation formats and pulse-shaping technologies. Analog bandwidth of DACs is one of the major limiting factors for the system capacity. In this paper, we present an idea to extend the analog bandwidth of DACs by utilizing a digital preprocessor, two sub-DACs, and an analog multiplexer (AMUX). The AMUX is a high-speed linear selector, and a frequency-domain interpretation of the AMUXs function has led us to devise the digital preprocessing for a seamless extension of the analog bandwidth. This configuration, which we call a digital-preprocessed analog-multiplexed DAC, provides nearly doubled analog bandwidth compared to that of each subDAC with a symmetric configuration. The idea was verified by a transmission experiment with 160-Gb/s 80-Gbaud Nyquist four-level pulse amplitude modulation. In the experiment, we used subDACs with an analog bandwidth of ~20 GHz in combination with an AMUX fabricated with InP heterojunction bipolar transistor technology.

A Compact EADFB Laser Array Module for a Future 100-Gb/s Ethernet Transceiver

A 4 × 25-Gb/s electroabsorption modulator integrated with a distributed feedback (DFB) laser (EADFB laser) array monolithically integrated with a low-loss optical multiplexer (MUX) is developed for 100 GbE transmitters for the first time. A cascaded Mach-Zehnder (MZ) filter, which has no intrinsic loss, is used as the MUX. The design and fabrication of the MZ-MUX for 100 GbE are thoroughly described. The measured loss of fabricated MZ-MUX is 2-3 dB, which is improved by 4 dB compared with that of the conventional 1 × 4 multimode interference MUX. The MZ-MUX is monolithically integrated with a four-EADFB-laser array and the output power of the chip is increased by 3 dB compared with that of a conventional 4 × 25-Gb/s monolithically integrated chip. With the folded layout, the size of the chip is similar to that of the conventional chip. The fabricated chip is packaged into a very compact transmitter optical subassembly (TOSA). The system requirements are satisfied with semi-cooled operation, and very clear eye openings are obtained after 10-km single-mode-fiber transmission. The adjustment of filter spectra by current injection is also shown, and fine tuning is possible with very low injection current.

Ultra-Compact 100 GbE Transmitter Optical Sub-Assembly for 40-km SMF Transmission

We design and fabricate wide wavelength range directly modulated lasers (DMLs) on the same InP wafer to realize a large-capacity monolithically integrated light source array up to 1 Tb/s. We demonstrate a 25.8-Gb/s push-pull operation over a 30-nm wavelength range, which is conventionally about 14 nm for 100 GbE applications. To extend the operating wavelength range, we design the wavelength dependence of the differential gain (∂G/∂n) for an InGaAlAs multiple quantum well structure, and realize high frequency relaxation oscillation resulting from the high differential gain over a wide range. Next, we also design the wavelength detuning (Δλ) under an operating injection current condition by taking account of the thermal effect of the chip, because Δλ determines ∂G/∂n, and the threshold current of the laser diode (LD). In addition, to achieve a 25.8-Gb/s push-pull operation, we fabricate a ridge waveguide structure buried in benzocyclobutene (BCB) with a low parasitic capacitance, and electrically isolate the DML from the neighboring chip by etching off n-InP. By using this design and structure, we achieve a 3-dB-down frequency bandwidth of over 20 GHz from 1290 to 1320 nm. We also achieve a mean output power of 8.0 dBm, and a dynamic extinction ratio of 5 dB. We measure the 25.8-Gb/s transmission characteristics, and obtain clear eye openings for a back-to-back configuration. We also measure the bit-error-rate performance, and obtain error-free operation for a 30-nm operating wavelength range.

Flip-Chip Interconnection Lumped-Electrode EADFB Laser for 100-Gb/s/

The first ultracompact transmitter optical subassembly for long-distance, beyond-100-Gbit/s data communication systems based on a monolithically integrated light source is developed, and 40-Gbit/s× 4 operation with the clear eye openings up to 10-km single mode fibre transmission is demonstrated.

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We propose a novel 16QAM signal generation method using a single Mach-Zehnder modulator. We successfully demonstrate 50 Gbit/s 16QAM signal generation with a dual-drive npin InP Mach-Zehnder modulator using amplitude control by electro-absorption.