Ranovus shows 200 gigabit direct detection at ECOC

Ranovus has announced it first direct-detection optical products for applications including data centre interconnect.

Saeid AramidehThe start-up has announced two products to coincide with this week’s ECOC show being held in Dusseldorf, Germany.

One product is a 200 gigabit-per-second (Gbps) dense wavelength-division multiplexing (WDM) CFP2 pluggable optical module that spans distances up to 130km. Ranovus will also sell the 200Gbps transmitter and receiver optical engines that can be integrated by vendors onto a host line card. 

The dense WDM direct-detection solution from Ranovus is being positioned as a cheaper, lower-power alternative to coherent optics used for high-capacity metro and long-haul optical transport. Using such technology, service providers can link their data centre buildings distributed across a metro area. 

The cost [of the CFP2 direct detection] proves in much better than coherent 

“The power consumption [of the direct-detection design] is well within the envelope of what the CFP2 power budget is,” says Saeid Aramideh, a Ranovus co-founder and chief marketing.  The CFP2 module's power envelop is rated at 12W and while there are pluggable CFP2-ACO modules now available, a coherent DSP-ASIC is required to work alongside the module.  

“The cost [of the CFP2 direct detection] proves in much better than coherent does,” says Aramideh, although he points out that for distances greater than 120km, the economics change.

The 200Gbps CFP2 module uses four wavelengths, each at 50Gbps. Ranovus is using 25Gbps optics with 4-level pulse-amplitude modulation (PAM-4) technology provided by fabless chip company Broadcom to achieve the 50Gbps channels. Up to 96, 50 Gbps channels can be fitted in the C-band to achieve a total transmission bandwidth of 4.8 terabits. 

Ranovus is demonstrating at ECOC eight wavelengths being sent over 100km of fibre. The link uses a standard erbium-doped fibre amplifier and the forward-error correction scheme built into PAM-4.  

Technologies

Ranovus has developed several key technologies for its proprietary optical interconnect products. These include a multi-wavelength quantum dot laser, a silicon photonics based ring-resonator modulator, an optical receiver, and the associated driver and receiver electronics. 

The quantum dot technology implements what is known as a comb laser, producing multiple laser outputs at wavelengths and grid spacings that are defined during fabrication. For the CFP2, the laser produces four wavelengths spaced 50GHz apart. 

For the 200Gbps optical engine transmitter, the laser outputs are fed to four silicon photonics ring-resonator modulators to produce the four output wavelengths, while at the receiver there is an equivalent bank of tuned ring resonators that delivers the wavelengths to the photo-detectors. Ranovus has developed several receiver designs, with the lower channel count version being silicon photonics based.    

The quantum dot technology implements what is known as a comb laser, producing multiple laser outputs at wavelengths and grid spacings that are defined during fabrication. 

The use of ring resonators - effectively filters - at the receiver means that no multiplexer or demultiplexer is needed within the optical module. 

“At some point before you go to the fibre, there is a multiplexer because you are multiplexing up to 96 channels in the C-band,” says Aramideh. “But that multiplexer is not needed inside the module.”

Company plans

The startup has raised $35 million in investment funding to date. Aramideh says the start-up is not seeking a further funding round but he does not rule it out. 

The most recent funding round, for $24 million, was in 2014. At the time the company was planning to release its first product - a QSFP28 100-Gigabit OpenOptics module - in 2015. Ranovus along with Mellanox Technologies are co-founders of the dense WDM OpenOptics multi-source agreement that supports client side interface speeds at 100Gbps, 400Gbps and terabit speeds. 

However, the company realised that 100-gigabit links within the data centre were being served by the coarse WDM CWDM4 and CLR4 module standards, and it chose instead to focus on the data centre interconnect market using its direct detection technology. 

Ranovus has also been working with ADVA Optical Networking with it data centre interconnect technology. Last year, ADVA Optical Networking announced its FSP 3000 CloudConnect data centre interconnect platform that can span both the C- and L-bands. 

Also planned by Ranovus is a 400-gigabit CFP8 module - which could be a four or eight channel design - for the data centre interconnect market.  

Meanwhile, the CFP2 direct-detection module and the optical engine will be generally available from December.