Author:  ShuhuiLi     2015-12-31

With the rapid develop of information era, there is an increasing demand on the transmission capacity of communication systems. The existing fiber optical communication systems face great challenge. Lots of new techniques are emerging to overcome the capacity crunch of optical communications, among which fiber-based orbital angular momentum (OAM) communications may provide a possible solution.

Jian Wang’s group at Wuhan National Laboratory for Optoelectronics (WNLO), Multi-Dimensional Photonics Laboratory (MDPL), has been devoted to the research of fiber OAM communications for many years and achieved a series of progress:

In order to realize high-performance OAM transmission (i.e. high speed, large capacity, high spectral efficiency, good stability, low nonlinearity), directed By Prof. Jian Wang, PhD candidate Shuhui Li from MDPL proposed two kinds novel OAM fiber structures. First, Shuhui Li presented a compact (130 μm cladding diameter) trench-assisted multi-orbital-angular-momentum (OAM) multi-ring fiber with 19 rings each supporting 22 modes with 18 OAM ones (Scientific Reports, 4, 3853, 2014).Using thehigh-contrast-index ring and trench designs, the trench-assisted multi-OAM multi-ring fiber(TA-MOMRF) features both low-level inter-mode crosstalk and inter-ring crosstalk within a widewavelength range (1520 to 1630 nm), which can potentially enable Pbit/s total transmission capacity andhundreds bit/s/Hz spectral efficiency in a single TA-MOMRF. Then, Shuhui Li proposed a multi-OAM multi-core supermode fiber (MOMCSF) for OAMtransmission (Optics Express 23, 18736-18745, 2015).The MOMCSF featuressuperior properties such as low nonlinearity, low mode coupling, and large fabricationtolerance, which may find wide potential use in long-distance OAM multiplexingtransmission systems and other OAM communication applications

Figure 1 (a)Structure of a 19-ring trench-assisted multi-OAM multi-ring fiber (TA-MOMRF). (b) Three dimensional structure and cross-section of a multi-OAM multi-core supermodefiber (MOMCSF) for OAM transmission.

To satisfy the requirements of providing highcapacity, high split-ratio, and long transmission distance in next-generation access networks, directed by Prof. Jian Wang, PhD candidatesAndong Wang, Long Zhu, and Jun Liu cooperating with Dr. Cheng Du and Mr. Qi Moin Fiberhome Telecommunication Technologies Co. Ltd,demonstrated theproof-of-concept experiment of hybrid mode-division multiplexing (MDM)and time-division multiplexing (TDM) passive optical network (PON) architecture by exploitingOAM modes (Optics Express 23, 29457-29466, 2015).The obtainedresults imply that a hybrid combination of OAM multiplexing and TDM technique mightprovide a promising approach to facilitating future high-capacity optical access networks.Andong Wang, Long Zhu, and Jun Liu contributed equally to this work.

Figure 2Schematic of the proposed MDM-TDM-PON architecture (hybrid OAM multiplexingand TDM PON).

Moreover, Prof. Jian Wang’s group designed two kinds of fiber converter to realize low-cost, versatile all-fiber OAM conversion. PhD candidate Liang Fang proposed fiber helical gratings (HGs) for flexible generation, conversion, and exchange of fiberguided OAM modes (Optics Letters 40, 4010-4013, 2015).It is expected that the proposed scheme is a promising method for fiber-based generation,date exchange, and spectra processing of OAM modes, and mayhave some potential applications in OAM multiplexing in fibercommunications. In addition, directed by Prof. Jian Wang, cooperating with Dr. Cheng Du and Mr. Qi Mo in Fiberhome Telecommunication Technologies Co. Ltd,PhD candidate Shuhui Li, demonstrated a scheme to realize a controllable, scalable, low-cost,and versatile all-fiber OAM converter(Optics Letters 40, 4376-4379, 2015) (ranking 2nd in the top 10 download in the publishing month).The converter consists of a two-modefiber (TMF) with its input terminal welded with a single-mode fiber, a mechanical long-period grating (LPG),a mechanical rotator, metal flat slabs, and a fiber polarization controller.The proposed simple, scalable, low-cost, and versatile mode generator may seepotential applications in mode-division multiplexing, opticalmanipulation, and other interesting fields.

Figure 3 (a) Scheme of helical gratings (HGs) OAMconverter. (b) Principle of controllable all-fiber OAM converter.

 

These works are partially supported by the National Basic Research Program of China (973Program) (2014CB340004), the NationalNatural Science Foundation of China (NSFC) (11274131, 11574001, 61222502), the Program for New Century ExcellentTalents in University (NCET-11-0182),and the Wuhan Science andTechnology Plan Project (2014070404010201).

Links of the published papers:

[1] Shuhui Li and Jian Wang*, “A compact trench-assisted multi-orbital-angular-momentum multi-ring fiber for ultrahigh-density space-division multiplexing (19 rings × 22 modes),” Scientific Reports, 4, 3853 (2014).

http://www.nature.com/articles/srep03853

[2] Shuhui Li and Jian Wang*, “Supermode fiber for orbital angular momentum (OAM) transmission,” Optics Express 23(14), 18736-18745 (2015).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-14-18736

[3] Andong Wang, Long Zhu, Jun Liu, Cheng Du, Qi Mo, and Jian Wang*, “Demonstration of hybrid orbital angular momentum multiplexing and time-division multiplexing passive optical network,” Optics Express 23(23), 29457-29466 (2015).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-23-29457

[4] Liang Fang and Jian Wang*, “Flexible generation/conversion/exchange of fiber-guided orbital angular momentum modes using helical gratings,” Optics Letters 40(17), 4010-4013 (2015).

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-40-17-4010

[5] Shuhui Li, Qi Mo, Xiao Hu, Cheng Du, and Jian Wang*, “Controllable all-fiber orbital angular momentum mode converter,” Optics Letters 40(18), 4376-4379 (2015).

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-40-18-4376