Yozo Ishikawa

Sn–Ag–Cu Solder Reflow-Capable 28-Gb/s × 4-Channel High-Density Parallel-Optical Modules

This paper describes a unique solution to the next-generation high bit-rate and high channel-density parallel-optical links whereby the size of parallel-optical modules would have to be considerably reduced. Since the main problem concerning the size of optical-to-electrical conversion part is associated with the mounting of the parallel-optical module to the printed-circuit-board (PCB), this paper puts forward a remarkably compact parallel optical-module design that can be soldered directly onto the PCB. That is made possible by the high temperature tolerance of 250 °C required for Sn-Ag-Cu solder-reflow process. The miniature parallel-optical module measures only 10.5 mm in length, 6.5 mm in width, and 1.5 mm in height. The resulting parallel-optical modules are capable of four-channel error-free parallel pseudo-random binary sequence 231-1 transmission at 28 Gb/s without using clock and data recovery as well as feed-forward error correction (FEC); hence, these parallel-optical modules are applicable in next-generation high-density 100 Gb/s Ethernet applications that use FEC.

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.

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.

A fully engineered QSFP AOC using solderable 4-channel optical transceiver modules

In recent years, optical interconnects are attracting attention to achieve high-speed signal transmission in high-end routers, high-end servers, and high performance computing systems. In rack-to-rack applications, AOCs that have the same electrical interface as conventional electrical cables have been equipped in actual systems especially. On the other hand, board-to-board applications have been expected as the next-generation high-density optical interconnects supported by high-density mounting of parallel-optical modules nearby LSI. In order to meet both of demands, we developed 10-Gb/s × 4-channel parallel-optical modules that are capable to be mounted by Sn-Ag-Cu-solder-reflow process which is the most popular for handling other SMDs. The size of fabricated modules is as small as 12mm × 7.2mm × 1.5mm. We paid attention to minimize the thickness to realize a simple heat dissipation structure together with other SMDs. We achieved a very low height as same as 1.5mm in total. We tested transmission characteristics and achieved error-free transmission in back-to-back, OM2 of 100 m and OM3 of 100 m where a power-penalty is estimated to 1dB. Through experiments of transmitting all 4 channels simultaneously, we clarified that the modules have a sufficient jitter margin in all channel. And we verified Sn-Ag-Cu reflow temperature resistance of the modules based on JIS standard whose peak temperature is as high as 250°C (i.e., JIS C 60068-2-58). We evaluated output power variation in TX module and sensitivity variation in RX modules before and after test. Both optical power variation and sensitivity variation are less than ±10%. We also fabricated a small PCB whose edge is compliant with a standard QSFP+ connector and TX and RX modules are mounted a PCB through Sn-Ag-Cu-solder-reflow process. We performed primary reliability tests of temperature cycling, mechanical shock and vibration tests based on the specified conditions in Telcordia GR-468-CORE. As results, optical power and input sensitivity deviation are less than ±10% and transmission characteristics have no degradation in all tests.

1060-nm VCSEL-based 28-Gb/s × 4-channnel optical signal transmission beyond 500-m MMF using high-density parallel-optical modules

Optical interconnects has been a key technology to realize signal transmission in rack-to-rack application where active optical cables (AOCs) such as QSFP have been employed so far. At present, it is required to mount parallel-optical modules with high-density to increase multiple numbers of signals in board-to-board applications which are highly expected in the next order of rack-to-rack applications. On the other hand, power reduction is a key issue in the next generation board-to-board optical interconnects where a low power consumption as same as 10 mW/Gb/s/link is required based on the trend of power reduction. To realize low power optical interconnects, we have been proposing 1060-nm optical interconnects which also achieve high speed modulation, high reliability, and high signal quality. We fabricated TX and RX 1060-nm 10-Gb/s × 12-channel parallel-optical modules. The mechanical size is as small as 13 mm × 13 mm × 3.4 mm. Operating all 12 channels in TX and RX parallel-optical modules simultaneously, we have achieved error-free transmission over the case temperature range ranging up 15 °C to 80 °C in back-to-back. We also achieved error-free transmission for a legacy OM-2 multimode fiber of 300m with the power penalty less than 2.0 dB. By using high-efficient 1060 nm VCSELs, power reduction is expected where we achieved optical link power of 7 mW/Gb/s/link at the case temperature of 80 °C. We performed reliability tests based on Tercordia GR-468. The results show that the optical modules are highly reliable since the variation of optical output power is less than ±10 % in all reliability tests.

Sn-Ag-Cu-solder-reflow-capable 10-Gb/s × 4-channel very thin high-density parallel-optical modules

We demonstrate >1.3-Tb/s VCSEL-based on-board optical module for high-density optical interconnects. The optical module integrates 28-Gb/s × 24-channel transmitter and receiver into one package of 1-inch^2 footprint. Subsequently, the total data rate is as high as 1.34 Tb/s. As investigated the temperature distributions of an optical module in calculation and experiment, an operating case temperature of optical module is lower than the maximum case temperature of 70 degree C in a practical air-cooling environment with the total power consumption of 9.1 W when activating all CDR circuitries as the harshest condition. The module exhibits a total jitter margin of 0.48 U. I. at a BER of 10^-12 when operated by a 28.05-Gb/s NRZ PRBS bit stream for each channel. By bypassing CDR circuitries with a capable length of electrical transmission line of 30 mm, a jitter margin was degraded to 0.21 U. I. at a case temperature of 70 degree C. If a system accepts such a level of jitter margin, the total power consumption can be suppressed to 6.0 W and an operating case temperature can be decreased accordingly.