IEEE Computer Society LMU Event

Tbit/s Optical Communications using Orbital Angular Momentum

Alan E. Willner

University of Southern California, Los Angeles, CA 90089, USA

We acknowledge the support of DARPA

Thank You!!!!

… to Dr. Mehrdad Sharbaf for his kind invitation. … to all my wonderful students and colleagues.

USC’s OCLab Family

Ø  Wavelength-division multiplexing (WDM)

Ø  Time-division-multiplexing (TDM)

Ø  Polarization-division multiplexing (PDM)

Ø  Space-division multiplexing (SDM)

Ø Free-space communication links using orbital angular

momentum (OAM) modes 1. OAM eigenstates are orthogonal 2. Potential for high spectral efficiency and capacity

Motivation: OAM Modes

4

Miscellaneous Multiplexing Approaches

Mode-Division Multiplexing

High capacity communications using OAM beams

v  Increase system capacity using beams carrying OAM v  Use multiple orthogonal approaches

High Capacity

Polarization- division-

multiplexing

Wavelength- division-

multiplexing

OAM mode-division- multiplexing

OAM with +/- charge multiplexing

5  

Space-division-multiplexing

(Concentric rings)

Higher-order modulation formats

(multiple bits/symbol)

Outline

1.  OAM Beam (De)multiplexing

2. Optical Communications using OAM

- Pol-muxing, WDM

- MIMO

3.  Turbulence Emulation and Compensation

4.  OAM in Vortex “Ring” Optical Fibers

5.  OAM-Based Networking Functions

- Exchange, ROADMs

7

-10 -8 -6 -4 -2 0 2 4 6 8

x 10-4

-10

-8

-6

-4

-2

0

2

4

6

8

x 10-4

[m]

[m]

-10 -8 -6 -4 -2 0 2 4 6 8

x 10-4

-10

-8

-6

-4

-2

0

2

4

6

8

x 10-4

[m]

[m

]

-10 -8 -6 -4 -2 0 2 4 6 8

x 10-4

-10

-8

-6

-4

-2

0

2

4

6

8

x 10-4

-10 -8 -6 -4 -2 0 2 4 6 8

x 10-4

-10

-8

-6

-4

-2

0

2

4

6

8

x 10-4

l = 0 l = 1

l = 2 l = 3

# of states possible = infinite! , …. ( theoretically)

l = …. -3, -2, -1 ,+1, +2, +3 ….

o  Intensity null at the center o  Phase spirals ‘l’ times over distance of one wavelength

‘No OAM’

Orbital Angular Momentum – LG Beams : Concept

# of states possible = 2

and

# of states possible = 2

and

Linear Polarized Light Circularly Polarized Light

Orbital Angular Momentum

Alison M. Yao, et al. Adv. in Opt. & Phot., 2011

8

Generation and Detection of OAM (LG beams) : Concept

Incoming Gaussian beam

Converted into LG beam, carrying OAM

Incoming LG beam

Re-converted into Gaussian

Spatially de-multiplexed

@ Transmitter

@ Receiver

Holographic phase filter

Holographic phase filter

Desired spatial phase function

Grating structure

Alison M. Yao, et al. Adv. in Opt. & Phot., 2011

General Concept of OAM Link

A. Willner, Science, Aug. 10, 2012

OAM (0,-8)

OAM (0,+10)

OAM (0,+12)

OAM (0,-14)

Beam Splitter-Based

Multiplexing

SuperImposed OAMs

OAM (0,-8)

OAM (0,+12)

OAM (0,-14) Data 1

Data 3

Data 2

Data 4 OAM (0,+10)

Intensity Phase

Intensity Phase

Intensity Phase

Intensity Phase

Intensity

Charge “-8”

Charge “+10”

Charge “+12”

Charge “-14”

Data 1

Data 2

Data 3

Data 4

Phase Pattern Applied to Gaussian

Gaussian

Gaussian

Gaussian

Gaussian

SLM-Based OAM Generation

Concept: Generation and Multiplexing of Multiple OAMs

OAM Demuxing by Geometrical Transformation: Mode Sorter

•  Geometric transformation produces a spot, the lateral position of which is proportional to the input OAM state.

•  Two optical components, (b) and (c), are required to carry out this transformation.

M. Lavery and M. Padgett

-1, -3, 0, +1, +3 “Loss-less”

Demux 0

-3-to-0

+1-to-0

-1-to-0

+3-to-0

Multi-level Modulaton Formats in Optics

Benefits from coherent detection: •  More effective for pol-demuxing •  Digital processing for mitigation

1 bit/symbol 2 bits/symbol 4 bits/symbol

~112 Gbaud OOK DPSK

DB/PSBT

~56 Gbaud DQPSK (4-ASK)

~28 Gbaud PDM-(D)QPSK

(16-DPSK)

Im{Ex}

Re{Ex} ( )

Im{Ex}

Re{Ex}

Im{Ex}

Re{Ex}

Im{Ey}

Re{Ey}

8 bits/symbol

~14 Gbaud 16-QAM

8-PSK/2-ASK

Im{Ex}

Re{Ex}

Im{Ey}

Re{Ey}

Reference: R. Essiambre and P. Winzer, Alcatel/Lucent

12.8-bit/s/Hz Spectral Efficiency"Phase Patterns Loaded to SLM1-SLM4"

Charge “+8”" Charge “+10”" Charge “+12”" Charge “+14”"

SLM1" SLM2" SLM3" SLM4"

Intensity Profiles of OAM Modes"

OAM (0,-8)" OAM (0,+12)" OAM (0,-14)"OAM (0,+10)"Superimposed

Four OAM Modes"OAM(0,-8) Demultiplexing"

Only SLM1 On"Without crosstalk"

Only SLM1 Off"Crosstalk only"

SLM1-4 On"With crosstalk"

Only SLM4 On"Without crosstalk"

Only SLM4 Off"Crosstalk only"

SLM1-4 On"With crosstalk"

OAM(0,-14) Demultiplexing"

13 J. Wang, Nature Photonics, June, 2012

Optical Spectra"

12.8-bit/s/Hz Spectral Efficiency"

BER Performance"Four OAM Modes: OAM(0,-8), OAM(0,+10), OAM(0,+12), OAM(0,-14) "

q  Without crosstalk: only the desired OAM mode is present while others are off."q  With crosstalk: all OAM modes are on when demultiplexing the desired OAM mode."q  The crosstalk of demultiplexing for OAM(0,-8), OAM(0,+10), OAM(0,+12), and " OAM(0,-14) is measured to be -24.7, -24.0, -20.4 and -24.0 dB, respectively."q  Less than 1.2 dB OSNR (optical signal-to-noise ratio) penalty is measured at a BER " of 2e-3 without crosstalk."q  A total OSNR penalty of less than 2.2 dB at a BER of 2e-3 is observed with crosstalk. "14 J. Wang, Nature Photonics, June, 2012

12.8-bit/s/Hz Spectral Efficiency"

Constellation: Demultiplexed OAM Modes (Without Crosstalk)"

OAM(0,-8)" OAM(0,+10)" OAM(0,+12)" OAM(0,-14)"

Constellation: Demultiplexed OAM Modes (With Crosstalk)"

OAM(0,-8)" OAM(0,+10)" OAM(0,+12)" OAM(0,-14)"EVM: error vector magnitude!15

Diagram: Generation/Mux/Demux of Pol-Muxed Multiple OAMs"

q Spatial light modulators (SLM) convert input Gaussian mode to OAM modes."q Inverted phase pattern is used to demultiplex OAM modes."q OAM+8 and OAM-8 have the same size of intensity profiles."

16

q  We measure the crosstalk of OAM demultiplexing from superposed" pol-muxed OAM modes, which is assessed to be less than -18 dB."

17

Crosstalk Measurement"

Pol-Muxed Four OAM Modes: OAM+4, OAM+8, OAM-8, OAM+16"

Spatial DE-MUX

Beam splitter

Spatial-filter

Concept: Spatial-Multiplexed OAMs (Concentric Rings)

Multiple OAMs

Multiple OAMs

Same charge, different data

q  Different data streams can be encoded on two group of OAM beams, with the same

charge but different ring radius.

q  A spatial filter (or a specially designed grating) can be used to demux the inner ring and

the outer ring

Outer ring

Inner ring

Lens  400mm  Lens  

(a)

(b)

EDFA  

BS  1x4  OC  

SLM-­‐1  HWP  Col  

EDFA  BPF   A>  EDFA  

SLM-­‐5  (Demux)  

I/Q  Mod.  

Laser   BPF  PC  

16QAM  GeneraIon  

Fiber  

SLM-­‐2  

SLM-­‐3  

SLM-­‐4  Mirror  

Camera  

PolarizaIon  Diversity    90

0-­‐Hybrid  

ADC  

ADC  

ADC  

ADC  

Off-­‐line  DSP  

EDFA  

LO  

Col  

QPSK   16QAM  

OSA  1%  tap  

2  x  20  Gbit/s  

BS  

BS  

6dB  a>en.

Φ

BS   BS  

BS  BS  

PBS   PBS  

Lens   Lens  1:2    

expansion  

3:1    compression  

Lens  

SpaIal    filter  

HWP  

DE-­‐MUX

Pol.  

Coherent  DetecIon  

HWP  

MR  MR   MR  MR   MR  

Mode-­‐MUX +/-­‐  Charge Pol-­‐MUX Space-­‐MUX

MUX

Ø  32 data channels carried by OAM beams are multiplexed in two concentric rings. Ø  Each channel uses 20 Gbaud/s 16-QAM signal. Ø  The total capacity is 2.4 Tbit/s, with a spectrum efficiency of 95.7 bit/s/Hz considering 7% FEC overhead (102.4 bit/s/Hz without considering 7% FEC overhead)

Experimental Setup of 32 OAM Channels Multiplexing Toward Spectral Efficiency of ~95 bits/sec/Hz

OAM  +10 OAM  +12 OAM  +14 OAM  +16

4  modes    

Inner  ring  a_er  demux Out  ring  a_er  demux

MUX/DEMUX Images

8  modes     16  modes     32  modes  

Pol-­‐muxed    OAM  ±10~  ±16

OAM  ±10~  ±16 OAM  +10~+16 Two  rings  of  Pol-­‐muxed    OAM  ±10~  ±16

Ø  Two concentric rings are demultiplexed using a spatial filter.

SpaIal  filter SpaIal  filter

J. Wang, Nature Photonics, June, 2012

1549.4 1549.6 1549.8 1550.0 1550.2 1550.4 1550.6-­‐60

-­‐50

-­‐40

-­‐30

-­‐20

-­‐10  w/  c ros s talk  w/o  c ros s talk

Power

 (dBm)

Waveleng th  (nm)

30dB

25GHz

Optical Spectrum of the 20 Gbaud/s16-QAM Signal after Demultiplexing

Ø  Considering 20Gbaud 16-QAM signal on 32 OAM channels with 7% FEC overhead, an aggregate SE of 95.7 bit/s/Hz (80*32/25/1.07) is achieved. (SE= 102.4 bit/s/Hz without considering 7% FEC overhead） Ø  Total capacity of 2.56Tbit/s on a single wavelength.

J. Wang, Nature Photonics, June, 2012

(d)  EVM  9.6(b)  EVM  8.68 (c)  EVM  9.5

(a)  EVM  7.5

Outer  ring  x-­‐pol

OAM  +10

(f)  EVM  8.5(e)  EVM  8.4 (g)  EVM  8.8Inner  ring  y-­‐pol

OAM  -­‐16

Back  to  back

No  crosstalk Single  ring Two  rings

Recovered Constellations of Two Typical Channels (Inner ring OAM -16 & Outer ring OAM +10)

Ø  Recovered Constellations shows a very little penalty due to the concentric ring multiplexing.

J. Wang, Nature Photonics, June, 2012

23 23

High capacity data link using OAM and WDM

OAM value

Wavelength Independent channels

Concept of combining OAM and WDM

Ø  OAM multiplexing and WDM are in two different domains (spatial and wavelength), and they are compatible in a transmission link."Ø  Combining OAM and WDM increases available independent channels and consequently the transmission capacity."

24 24

Procedure of generating 24 OAM beams

OAM    value

+4 +7 +10 +13 +16 +19

+4 +7 +10 +13 +16 +19 -­‐4 -­‐7 -­‐10 -­‐13 -­‐16 -­‐19

Y-­‐pol

X-­‐pol

OAM    value

+4 +7 +10 +13 +16 +19 -­‐4 -­‐7 -­‐10 -­‐13 -­‐16 -­‐19

+7 +13 +19

+4 +10 +16 OAM    value

OAM  value

OAM  value

SLM1

SLM2

(a)

(b)

(c)

Ø  Each SLM generate 3 OAM modes that are far way from each other, so that their internal crosstalk to each other is <-32dB."Ø  Mirrors and half-wave plates are used to generate reversed charged and polarization multiplexed OAM beams."

6 modes

12 modes

24 modes

25

-­‐50

-­‐40

-­‐30

-­‐20

-­‐10

0

Power

 (dBm)

 P ower  of  des ired  OAM  c hannel  P ower  from  all  other  OAM  c hannels

-19 -13 -7 +7 +13 +19 X-pol Y-pol OAM value

-19 -13 -7 +7 +13 +19

-16 -10 -4 +4 +10 +16 -16 -10 -4 +4 +10 +16

Measured power distribution of each OAM channel.

XTalk

Ø  The difference between the power of desired OAM channel and the power from all other OAM channels indicates the external crosstalk."Ø  The measured largest crosstalk is -16.2 dB.

26

1530 1540 1550 1560 1570-100

-80

-60

-40

-20

Wavelength (nm)

Powe

r (dB

m)

demux OAM+10 from OAM+4,+10,+16

demux OAM+13 from OAM+4,+10,+16

XTalk

Optical spectrum after demux (x-pol, OAM+10)

The  wavelength  dependence  for  the  crosstalk  is  very  small  over  the  wavelength  range  from  1530-­‐1570  nm.

27

BER and OSNR for all 1008 channels

0 100 200 300 400 5008

7

6

5

4

3

2

1

 B  C

C hannel  Number

-­‐log10(B

ER)

E F E C  thres hod

10

15

20

25

30

35

40

OSNR  (d

B)

500 600 700 800 900 10008

7

6

5

4

3

2

1

 B  C

C hannel  Number

-­‐log10(B

ER)

E F E C  thres hod

10

15

20

25

30

35

40

OSNR  (d

B)

BER

OSNR

BER

OSNR

FEC  threshold FEC  threshold

X-­‐pol Y-­‐pol

Ø  The measured BER and OSNR for all 1008 (42×24) channels. "Ø  All of the channels can achieve a BER of < 3.8×10−3 (the limit for 7% overhead FEC)

FEC Codes in OAM Mode Multiplexed System

Motivation: LDPC Codes — Capacity Approaching Codes

Ø LDPC coding can help system performance.

Experiment Block Diagram

LDPC Coded 100-Gbit/s

QPSK"

4 OAM modes multiplexing using SLMs

OAM demulitplexing"

using SLM"

Off-line DSP and

LDPC decoding"

λ1 Free-space

transmission"

q  Data sequence is encoded through LDPC encoder and fed into 100-Gbit/s transmitter"q  OAM multiplexing: 4 OAM modes are multiplexed using 4 SLMs"q  Demultiplexing: An SLM converts one of the multiplexed OAM modes back to the Gaussian beam"q  The converted Gaussian beam is coupled into fiber for detection and followed by off-lined processing and decoding"

Experimental Results: BER Vs OSNR for OAM+12 and OAM+14 Channels

6 8 10 12 14 16 181E -­‐6

1E -­‐5

1E -­‐4

1E -­‐3

0.01

0.1  +12,  no  c rk,  no  c d  +12,  no  c rk,  w/  c d  +12,  w/  c rk,  no  c d  +12,  w/  c rk,  w/c d  +14,  no  c rk,  no  c d  +14,  no  c rk,  w/  c d  +14,  w/  c rk,  no  c d  +14,  w/  c rk,  w/c d

BER

O S NR  (dB )

q  The BER performance for demuxed OAM+12/OAM+14 with and without crosstalk."q  The coding gain of LDPC(8547, 6922) is about 5.8 dB, 7.0 dB/5.7 dB, 7.3 dB at BER= 10-5 for OAM+12 / OAM+14 without and with crosstalk. "

Coding Gain

4×4 MIMO Equalization for OAM crosstalk Mitigation

 

Distorted OAM l1

Distorted OAM l2

Distorted OAM l3

Distorted OAM l4

OAM l1

OAM l2

OAM l3

OAM l4

Received power

MIM

O

Equalization

OAM mode

OAM model1 l1 l2 l3l4l5

Power Power

Pure OAM mode Distorted OAM mode

(a) (b)

OAM l1

OAM l2

OAM l3

OAM l4

MUX

Propagate

Transmitted power

Concept of MIMO for OAM multiplexed system  

Distorted OAM l1

Distorted OAM l2

Distorted OAM l3

Distorted OAM l4

OAM l1

OAM l2

OAM l3

OAM l4

Received power

MIM

O

Equalization

OAM mode

OAM model1 l1 l2 l3l4l5

Power Power

Pure OAM mode Distorted OAM mode

(a) (b)

OAM l1

OAM l2

OAM l3

OAM l4

MUX

Propagate

Transmitted power

H. Hao et al., ECOC 2013

 

EDFA

I/QMod.

Laser

BPFPC

QPSK Generation

QPSK

2 x 10 Gbit/s

OAM+2 Genera. OAM+4Genera.

OAM+6Genera.

OAM+8 Genera.

DEMUXOAM+2 DEMUX OAM+4

DEMUX OAM+6 DEMUX OAM+8

ADC

ADC

ADC

ADC

Offline processing

LOOAM Generation/MUX/DEMUX

OAM

MU

X

Free-spacetransmission

OC

OC

OC

OC

Heterodyne Detection

SMF

SMF

SMF

Experimental Results —MIMO Equalization

 

CH1 CH2. CH3 CH4

CH1 CH2. CH3 CH4Without  MIMO  Equalization

With  MIMO  Equalization

 

21 22 23 24 25 26 276

5

4

3

2

1

 w/o  MIMO  w/  MIMO ,  7  taps  w/  MIMO ,  21  taps

-­‐log10

(BER)

O S NR  (dB )

F E C  thres hold

Recovered constell. with and w/o MIMO BER Vs. OSNR under different taps

q  The crosstalk on each channel is ~-19 dB, ~-12 dB, ~-11dB and ~-7 dB.

H. Hao et al., ECOC 2013

Measured crosstalk for this channel is ~ 12.5 dB.

Outline

1.  OAM Beam (De)multiplexing

2. Optical Communications using OAM

- Pol-muxing, WDM

- Coding, MIMO

3.  Turbulence Emulation and Compensation

4.  OAM in Vortex “Ring” Optical Fibers

5.  OAM-Based Networking Functions

- Exchange, ROADMs

OAM Propagation in Atmospheric Turbulence

Turbulence Emulator

Atmospheric Turbulence

Rotating Phase Plate

Transmitted OAM Distorted OAM

q  OAM beam will experience turbulence-induced distortion, which will result in channel crosstalk and system power penalty q  The atmospheric turbulence is emulated in the lab environment by using rotating phase plates, obeying Kolmogorov spectrum statistics

Y.  Ren,  CLEO2013,  Invited

Experimental Results —Crosstalk Measurement

= 2.5×10-16 = 0.0049

D/r0 = 0.239 F= 6.71

= 2.5×10-16

D/r0 = 0.438

= 0.0049

F= 11.35

F= 6.71

= 2.2×10-14 D/r0 = 3.94

= 0.46

F=11.35

= 2.2×10-14 D/r0 = 6.37

= 0.46

Weak Turbulence Strong Turbulence

Average crosstalk under different turbulence strength

10 mV/div

Average BER

Average BER Y. Ren, CLEO2013, Invited

35

OAM Turbulence Compensation — Concept

Beam separator

Feedback controller

WavefrontCorrector

Beam splitter

WavefrontCorrector

WavefrontSensor

Corrected OAM beams

Corrected Gaussian beam

Gaussian beam

OAM beams

Turbulence Emulator

Free Space Propagation Adaptive Optics Compensator

p   Use  Gaussian  beam  as  a  pilot  beam  to  detect  wavefront  distorCon  of  Gaussian  beam  by  using  conversional  WFS.  

p   ConvenConal  adapCve  opCcs  approach  could  not  work  for  OAM  beam      

36

Experiment Results— Far Field Images

Far Field Images

q  By using the correction pattern obtained from Gaussian pilot beam in AO system, the distorted OAM beams up to OAM l=9 are efficiently compensated.

(b2) (b3) (b4) (b5) (b6)

(a1) (a2) (a3) (a4) (a5) (a6)

OAM+1 OAM+3 OAM+5 OAM+7 OAM+9Gaussian  Beam

(b1)

RMS 0.613 PV 2.562 SR: 0.231

RMS 0.092 PV 0.649 SR: 0.924

Y.  Ren  et  al.,  ECOC  2013

37

Experimental Results — BER Performance

BER for channel OAM l = 5 before/after compensation

8 10 12 14 16 18 20 22 24 26

10-5

10-4

10-3

10-2

10-1

BER

OSNR (dB)

B2B Only Ch l = 5 After Comp. Only Ch l = 5 Before Comp. Ch l = 3, 7 On, After Comp. Ch l = 3, 7 On, Before Comp.

XT = -9.51 dB

FEC Limit

With  Comp. W/o Comp.  

Only l=5   -­‐27.85  dBm -­‐35.00  dBm

Ch l=3,7  on -­‐47.80  dBm -­‐44.51  dBmY.  Ren  et  al.,  ECOC  2013

Received power of OAM channel l=5"

Outline

1.  OAM Beam (De)multiplexing

2. Optical Communications using OAM

- Pol-muxing, WDM

- MIMO

3.  Turbulence Emulation and Compensation

4.  OAM in Vortex “Ring” Optical Fibers

5.  OAM-Based Networking Functions

- Exchange, ROADMs

OAM Mode Propagation Property in a Ring Fiber

N. Bozinovic et al., CLEO 2011"

Radially Polarized Beams in Ring Fiber

S. Ramachandran et al., OL 2009"

~1-km Ring Fiber Transmission of OAM Mode

Ø  ~1-km OAM mode transmission in ring fiber has been demonstrated. Ø  Increasing the supported OAM modes is highly desired to improve the spectral efficiency and capacity of the optical communications system.

N. Bozinovic, Science, vol.340, pp.1545-1548 (2013)

400 Gbit/s 4 Modes Data Transmission

B2B

DeMux BER

50Gbaud NRZ-QPSK, λ = 1550nm

Tx Mux

OAM + WDM Multiplexing: 1.6 Tbit/s Capacity

20 Gbaud/s 16-QAM + 10 Wavelengths over 2 OAM modes

N. Bozinovic, Science, vol.340, pp.1545-1548 (2013)

Experimental Results: 1.6 Tbit/s Capacity

q  OAM+ and OAM- have <-17dB crosstalk over 10 WDM channels with 0.8 nm channel spacing.

q  All of the channels achieved BER below the FEC limit of 3.8×10−3 with 20 Gbaud/s 16-QAM. q  A total of 1.6 Tb/s data transmission carried by OAM modes is achieved over 1.1 km vortex fiber.

N. Bozinovic, Science, vol.340, pp.1545-1548 (2013)

Outline

1.  OAM Beam (De)multiplexing

2. Optical Communications using OAM

- Pol-muxing, WDM

- MIMO

3.  Turbulence Emulation and Compensation

4.  OAM in Vortex “Ring” Optical Fibers

5.  OAM-Based Networking Functions

- Exchange, ROADMs

44 44

OAM-based Reconfigurable Optical Networking Functions

p Static point-to-point data transmission links

Space Division Multiplexing (SDM)

p Reconfigurable data pathsp Wavelength multiplexed and

time multiplexed networks

Networking Methods

p Channel Add/Dropp Data Exchangep Channel Multicasting

OAM based Optical Networking

Ø  Design and demonstrate several reconfigurable networking functions: p  A reconfigurable OAM channel add/drop multiplexer p  Multiple pairs of OAM channel data exchange p  Power equalized data multicasting in OAM systems

45 45

Add/drop function in OAM-multiplexed data link

...λ1 λ2 λnλ3 ...λ1 λ2 λnλ3

λ2

λ2/

/

Add

Drop

Ø In WDM networks, OADM has been demonstrated to selectively drop and add "a given wavelength channel without interrupting passthrough channels."

Ø A similar scheme can be implemented to selectively drop and add a given "OAM beam using SLM and spatial filters."

Wavelength Add/Drop Multiplexer Spatial Add/Drop Multiplexer for

OAM beams

Motivation

OAM charge"Wavelength" Wavelength"

Add/"drop"

OAM charge"

l1 l2 l3 lN l1 l2' l3 lN

l2'

l2

add"

drop"

46 46

Scheme concept of OAM Mode Add/Drop

Add/drop

Down-conversion Up-conversion

47 47

Principle of Add/drop multiplexer for OAM

To be added

Dropped beam

To be added

Dropped beam

grating

Ø The OAM mode to be dropped is down-converted to OAM0 which is in located in the beam center, while the rest OAM modes are rings that has no energy in the center."Ø The rings and the down-converted beam are reflected by different gratings, so that they can be separated without losing power.

48 48

Input: OAM-5,2,8 OAM+2 OAM-5 OAM+8

Down conversion

Up conversion

Drop OAM+2

Drop

The dropped channel

Add

Experimental results of add/drop: images

-  Multiplexing/demultiplexing of many OAM modes can be used as a technique for potentially increasing capacity and spectral efficiency.

- OAM is compatible with other optical communications techniques, such as WDM.

- OAM modes can be manipulated to achieve various networking functions.

Summary