OAM Switching: Main Achievements

One of the main objectives of ROAM project is to develop a OAM/WDM switch to significantly improve the scalability and the power consumption in data-centers applications

To achieve this goal, ROAM consortium makes use of internally developed integrated photonic devices that are designed and fabricated by the University of Glasgow, and then tested and inserted in a switching operation mode by CNIT.

A two-layer (OAM-WDM) optical switch has been designed within the project and presents the following main advantages and features:

- Architecture based on WDM and OAM modes. Each port is distinguished by the λ, each card is distinguished by the OAM mode

- Architecture based on Silicon integrated microrings as active switching elements and passive demultiplexing

- Power consumption/Gb/s < 1mW (>50x improvement of SoA)


 

OAM converter

An OAM converter exploiting an OAM demultiplexer based on refractive elements cascaded to an innovative integrated OAM multiplexer has been demonstrated. The OAM converter can operate on signals multiplexed both in OAM and wavelength domain. It has been tested up to 100Gb/s with real data-traffic showing good performance.

Working principle of the OAM converter for OAM-wavelength multiplexed signals (left), and proposed compact implementation (right).

Intensity profile of the OAM beam before and after the conversion.

3x3 Switch based on OAM integrated devices

A 3x3 switch exploiting an optical vortex beam emitter based on a silicon three-grating microring has been successfully deisgned and developed within ROAM project.

A silicon three-grating microring is proposed and characterized as a device enabling 3x3 optical switching based on orbital angular momentum and wavelength. Bit error rate measurements show penalties lower than 1dB for OOK traffic up to 20Gbaud.

(a) Mapping of the OAM mode order l emitted by the microring on the three gratings vs. wavelength li of the resonance peaks. (b) Scheme of a 3x3 OAM-based switch exploiting a three-grating microring and an OAM mode sorter. (c) Experimental setup for the characterization.

(a) BER vs. OSNR for switch configured as follows: S1 to O2, S2 to O3, S3 to O1. Output eye diagram in the inset. (b) BER vs. OSNR for switch configured as follows: S1 to O3, S2 to O3, S3 to O3. (c) Comparison of BER vs. OSNR at 20 and 30 Gbaud.

OAM-based integrated 2x2 optical switch

Within ROAM project, switching schemes have been found based on independent OAM modulators and multi-grating microrings. For the independent modulators case, different schemes have been poposed and studied.

A 2x2 OAM switch based on multi-grating microrings fabricated by UoG has been demonstrated and characterised for the first time. Spectral characterisations, mode purity measurements, bit-error rate (BER) measurements have been carried out up to 30 Gbaud with OOK, and 16QAM signals.

The aspect of networking exploiting OAM in conjunction to wavelength have also been investigated during ROAM activities.

A list of relevant networking parameters has been defined for the OAM conversion (Scalability, optical reach, number of hopes, bandwidth) and switching (scalability, blocking configurations, delay, bandwidth, reconfiguration time) systems. This parameters will be analysed during the WP6 activity, based on the data collected from experimental characerisations on the building blocks carried out in WP4 and on characterisations of OAM conversion and switching schemes carried out in WP6.

Two-layer optical switch

OAM switching schemes exploiting the cascade of an integrated OAM mux based on concentric Ω-shaped devices and the OAM demux based on cascaded refractive elements, developed and provided by UoG in WP4, have been also implemented and characterized. The exploited integrated OAM mux have been packaged at CNIT with fibre pigtails and electrical contacts to allow for OAM tuning. An integrated OAM mux (10 concentric OAM emitters) have been employed to demonstrate the full switching operation over 10 OAM modes and 16 WDM channels exploiting both 30 Gbaud OOK and 28Gbaud 16QAM signals. This experiments demonstrates the final Objective 2 of the ROAM project.

Setup for the testing of a 4x4 two-layer switch

OAM multiplexed transmission: crosstalk and power consumption investigation

The application of an automated software defined network (SDN) control system based on OpenFlow to a two-layer multi-port OAM-wavelength switch based on integrated concentric OAM modulators has been demonstrated. Results show that the overall switching time including the SDN-based OAM switch controlling system is successfully completed in less than 6ms.

 

OAM switch reconfiguration driven by the Open Flow agent

Integrated OAM mux with microlens tested in OAM switch setup

A packaged OAM mux chip with integrated microlens developed by IBM, has been delivered to CNIT and tested in a switching scheme, i.e. the chip has been cascaded to a refractive elements-based OAM demux. Measurements show good performance at 30Gbaud (OOK modulation).

 

OAM switch demonstrator with real data traffic

A demonstrator of the OAM-based switch has been carried out exploiting real data center equipment traffic. The switching demonstrator used the OAM-based switch two-layer architecture i.e. the cascade of an integrated OAM multiplexer based on 10 concentric -shaped waveguides and a refractive elements-based OAM demultiplexer, both developed by UoG. The field trial has been performed in different switch configurations, i.e. by tuning the order of the OAM mode emitted by the OAM mux and the input wavelength. The field trials are carried out for a two-port switch. The OAM switch worked stable also without FEC mechanism. A video file (ROAM promotional video) has been transmitted and displayed between server ends at full line rate. The latency between the server ends has been recorded and had no effect on the client side of the transmitted.

 

Screenshot of the ROAM promotional video transmitted through the OAM switch