ADCs key for high baud-rate coherent systems

Increasing the baud rate of coherent modems benefits optical transport. The higher the baud rate the more data can be sent on a wavelength, reducing the cost-per-bit of traffic.

But engineers have become so good at designing coherent systems that they are now approaching the Shannon limit. 

Tomislav Drenski

At the OFC show earlier this year, Ciena showcased a coherent module operating at 107 gigabaud (GBd). And last year, Acacia, now part of Cisco, announced its next-generation 1.2 terabits-per-second (Tbps) wavelength coherent module operating at up to 140GBd. 

The industry believes that increasing the baud rate to 240+GBd is possible, but each new symbol-rate hike is challenging.

All the components in a modem - the coherent DSP and its digital-to-analogue (DAC) and analogue-to-digital (ADC) converters, the optics, and the analogue drive circuitry - must scale in lockstep.

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Inphi adds a laser driver to its 100-gigabit PAM-4 DSP

Inphi has detailed its second-generation Porrima chip family for 100-gigabit single-wavelength optical module designs.

Source: Inphi

The Porrima family of devices is targeted at the 400G DR4 and 400G FR4 specifications as well as 100-gigabit module designs that use 100-gigabit 4-level pulse-amplitude modulation (PAM-4). Indeed, the two module types can be combined when a 400-gigabit pluggable such as a QSFP-DD or an OSFP is used in breakout mode to feed four 100-gigabit modules using such form factors as the QSFP, uQSFP or SFP-DD.

The Gen2 family has been launched a year after the company first announced the Porrima. The original 400-gigabit and 100-gigabit Porrima designs each have three ICs: a PAM-4 digital signal processor (DSP), a trans-impedance amplifier (TIA) and a laser-driver. 

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Has coherent optical transmission run its course?

Feature: Coherent's future

Three optical systems vendors share their thoughts about coherent technology and the scope for further improvement as they look two generations ahead to symbol rates approaching 100 gigabaud   

Optical transmission using coherent detection has made huge strides in the last decade. The latest coherent technology with transmitter-based digital signal processing delivers 25x the capacity-reach of 10-gigabit wavelengths using direct-detection, according to Infinera.

Since early 2016, the optical systems vendors Infinera, Ciena and Nokia have all announced new coherent digital signal processor (DSP) designs. Each new generation of coherent DSP improves the capacity that can be transmitted over an optical link. But given the effectiveness of the latest coherent systems, has most of the benefits already been achieved?

Source: Infinera

“It is getting harder and harder,” admits Kim Roberts, vice president, WaveLogic science at Ciena. “Unlike 10 years ago, there are no factors of 10 available for improvement.”

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MultiPhy readies 100 Gigabit serial direct-detection chip

MultiPhy is developing a chip that will support serial 100 Gigabit-per-second (Gbps) transmission using 25 Gig optical components. The device will enable short reach links within the data centre and up to 80km point-to-point links for data centre interconnect. The fabless chip company expects to have first samples of the chip, dubbed FlexPhy, by year-end.

Figure 1: A block diagram of the 100 Gig serial FlexPhy. The transmitter output is an electrical signal that is fed to the optics. Equally, the input to the receive path is an electrical signal generated by the receiver optics. Source: Gazettabyte

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Cortina unveils multi-channel dispersion compensation chip

Cortina Systems has announced its latest electronic dispersion compensation (EDC) chip.  The CS4342 is a compact device that supports eight duplex 10 Gigabit-per-second (Gbps) links. 

"Some customers are doing 2,000 signals at 10 Gig across the backplane"

Scott Feller, Cortina 

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The post-100 Gigabit era

Feature: Beyond 100G - Part 4

The latest coherent ASICs from Ciena and Alcatel-Lucent coupled with announcements from Cisco and Huawei highlight where the industry is heading with regard high-speed optical transport. But the announcements also raise questions too. 

Source: Gazettabyte

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2012: The year of 100 Gigabit transponders

Oclaro has detailed its 100 Gigabit coherent optical module that will be available from the second quarter of 2012. The MI 8000XM, a 5x7-inch 100 Gigabit-per-second (Gbps) transponder, uses NTT Electronics' (NEL) analogue-to-digital converter/ digital signal processor (DSP) ASIC at the receiver that compensates for transmission impairments.

“The world is moving to coherent, there is no question about that”

Per Hansen, Oclaro

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