VSFF connector in 400 and 800 Gigabit applications

What do they mean for the passive infrastructure? What applications do they make possible? What benefits do they bring?

Modern data centers have to cope with ever more exacting requirements. In addition to achieving maximum space savings and protection against potential system failures, the ability to support ever increasing speeds is growing in importance. In particular, applications that make use of AI (Artificial Intelligence) or ML (Machine Learning), as well as the increasing prevalence of home-office work, are leading to a growth in bandwidths. As a result, 400 Gigabit applications are becoming increasingly popular. And according to the Omdia-400G-beyond-Companion-Report such applications are set to grow enormously in 2023. The use of parallel lanes in optical transceivers is indispensable in order to transmit these ever increasing data rates. That is why the small VSFF connectors SN^® from Senko and MDC from US Conec have been developed for these parallel optical transceivers and are becoming increasingly common on the market.

Contents:

What 400G Ethernet applications are on the rise?
Who will win the race in the field of optical fiber connector interfaces?
Greatest advantage of the VSFF connectors: Port breakout directly at the transceiver
800 Gigabit Ethernet applications: A look ahead

What 400 Gigabit Ethernet applications are on the rise?

According to a study by Omdia, 400 Gigabit FR4 singlemode and 400 Gigabit DR4 singlemode are both set to enjoy vigorous growth. 400 Gigabit SR8 OM4 is the only multimode application with significant growth potential.

400G singlemode application - 400 Gigabit FR4

The data transfer speed of 400 GBit/s is achieved over four parallel full-duplex transmission channels (lanes) operating at 100 Gbit/s each with LC-Duplex (LC-Compact or LC Compact push-pull boot) in singlemode.

Singlemode LC-Duplex

LC-Duplex Push-Pull-Boot

400G singlemode application - 400 Gigabit DR4

Naturally, the transceivers for 400 Gigabit DR4 singlemode over 500 metres may come onto the market with MTP^®/MPO (4+4) SM APC 8°, PreCONNECT^® OCTO MTP^®, or also the SN^® Quad and MDC Quad interface. It is possible to connect these OCTO transceivers with our three PreCONNECT^® OCTO cabling systems: OCTO MTP^®, OCTO SN^® and OCTO MDC.

Singlemode MPO/MTP^®

4 + 4 (OCTO) with an APC 8° oblique cut

Singlemode MDC

MDC 4x (Quad-MDC)

©US Conec Ltd.

Singlemode SN^®

SN^® 4x (Quad SN)

400G multimode application – 400 Gigabit SR8

400 Gigabit SR8 is the only multimode among the 400G protocols to have major growth potential, described as MTP^® 16. This needs 8 lanes, 8 x 50 Gigabit, to achieve 400 Gigabits. That is why MTP^® 16 was developed a few years ago. The pin borings in this connector are slightly wider in order to provide space for the 16 fibers and the key is off-centre. What is new about this connector is that it is an MTP^® multimode which is cut to 8° APC for the first time, as is usually only done for singlemode.

The reason for this development is the PAM4-coded transmission (four-level pulse-amplitude modulation). Using PAM4 coding, 25G VCSEL is brought up to a lane speed of 50G. This PAM4 is extremely sensitive to noise, meaning that the return loss must be kept as low and stable as possible so that, if possible, no reflections are scattered back to the transmitter. This is possible using connector systems cut to 8°.

Singlemode MPO/MTP^®

MPO/MTP^®16 with an APC 8° oblique cut

Who will win the race in the field of optical fiber connector interfaces?

As described above, the optical transceivers for 400 Gigabits permit various options for the new VSFF (Very Small Form Factor) plug connectors. The new connector faces SN^® (SN = Senko Nano) from SENKO Co. Ltd. or MDC (Miniature Duplex Connector) from US Conec are on the way up. Both plug connectors have two sprung ceramic ferrules of diameter 1.25 mm based on LC technology.

Due to the size of the connectors and depending on the coupling configuration, a higher port density is possible in the 19” distribution panel than can be achieved with conventional connectors such as the LC-Duplex. The maximum possible with LC-Duplex is 96 ports per height unit (SMAP-G2 UHD). A sensible choice with MDC and SN^® is a maximum port density of 128 ports per height unit in the 19” distribution panel because this can still be patched without additional tools using the fingers alone.

The SN^® Quad interface, which has just appeared on the market, will be available as an alternative to the OCTO MTP^® and Quad MDC interfaces in the future. Here again, the SN^® Quad Uniboot is already in the development stage. The transceiver’s connector face is decisive in determining which of the connectors will be used.

The MDC is a VSFF connector that was specially developed to make these transceiver interfaces possible. The MDC’s are inserted individually directly into the transceiver. However, they can also be cascaded to form a block using a clip. Currently, work is also progressing on the MDC Quad Uniboot connector. However, there is still some way to go before it is introduced onto the market.

Greatest advantage of the VSFF connectors: Port breakout directly at the transceiver

The new VSFF plug connectors offer a decisive advantage compared to the conventional variant, namely port breakout. In the past, for example, parallelization has been implemented using an MTP^®/MPO connector over 4 so-called lanes to achieve the current value of 400 Gigabits. That corresponds to 100 Gigabits per lane to arrive at 400 Gigabits. In the future, these 400 Gigabits will increasingly be implemented by means of the new optical transceivers, for example with 4 MDC ports or alternatively 4 SN^® ports.

What is the advantage of the new OCTO MTP^®/MPO transceivers with MDC Quad and SN^® Quad interface compared to the OCTO MTP^®/MPO interface? Unlike the OCTO MTP^®/MPO interface, the four individual duplex ports at the MDC Quad and SN^® Quad interface can be disconnected directly at the transceiver interface for service work, for example for measurements, inspections and cleaning. By contrast, a harness or port breakout unit is always required for port breakouts at the conventional OCTO MTP^®/MPO variant. If service work is performed at a duplex port, then the MTP^®/MPO cannot be directly disconnected at the transceiver as otherwise the other three operational duplex ports also have to be shut down. With the new optical transceivers, the VSFF plug connectors can be led away directly from the transceiver by means of individual patchcords, e.g. for switches for server port breakouts. That is the main reason why these new small MDC and SN^® VSFF connectors were developed. Another advantage of the direct port breakout at the MDC Quad and SN Quad interface is the spine-leaf meshing using patchcords.

Image source: © SENKO Co. Ltd.

Another major plus in favour of these connectors is that they use ceramic technology together with all the benefits it brings. It is robust, offers extremely low insertion loss and a more stable, higher return loss than MTP^®/MPO technology. The compact design of the VSFF connectors helps save space in data centers and therefore also brings decisive advantages in terms of energy efficiency. You can find out more in the video:

800 Gigabit Ethernet applications: A look ahead

800 Gigabit DR8 is already available today and can be implemented conventionally with MTP^® 16 (PreCONNECT^® SEDECIM) in singlemode.

Singlemode MPO/MTP^®

4 + 4 (OCTO) with an APC 8° oblique cut

Singlemode MDC

MDC 4x (Quad-MDC)

©US Conec Ltd.

Singlemode SN^®

SN^® 4x (Quad SN)

Singlemode MPO/MTP^®

MPO/MTP^®16 with an APC 8° oblique cut

800 Gigabit DR4 singlemode transceivers with a reach of up to 500 metres will now come onto the market in their current state with SN^® Quad and MDC Quad interfaces.

Singlemode MDC

MDC 4x (Quad-MDC)

©US Conec Ltd.

Singlemode SN^®

SN^® 4x (Quad SN)

Author:
Harald Jungbäck, Product Manager FO cabling systems

Harald Jungbäck draws his fiber optic expertise from his many years of work at Rosenberger OSI. In 1993 he started his career in product and manufacturing process development. Today he is responsible for the consistent expansion of the product range and the technological innovation process in this area.

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