cdma_spie_02

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Code Division Multiple Access with MMI mineral
organic circuits
Y. Moreau1, K.Kribich1 , P. Coudray1 P. Etienne2,
J.Galy3 .
' Centre d'Electronique et de Micro-optoélectroniq
ue de Montpellier, Université Montpellier II,
France 2Laboratoire des Verres, Université
Montpellier II, France 3 Laboratoire
dInformatique, de Robotique et de
Microélectronique, Université Montpellier II,
France
2
Integrated optics

• Data Exchange 85 /year
• Voice traffic 10 /year

• Integrated optics was a next day technology for
  thirty years !

• 55 of Europeans have not yet emails.
• IDC (consultant) predicts 28 millions of
  connected objects to the Web sold in 2002 in the
  US

gt Now optical technologies have their  niche 
channel multiplication and broad band
transmission..
gt high demand for high rate.

• Available rates reaches now 5 Terabits/sec

 DWDM has proven to be one of the hottest niches
in the telecommunications market. 

• Highways for telecoms rather underwater (optical
  fibres) than in the sky (satellites).

DWDM market US 8 billions in 2003
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Materials for Integrated Optics
Electronics Compatibility
Active Circuits
Optical fiber Compatibility
Passive Circuits
Cost
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Semi-conductors
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Glasses
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Dielectric layers
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Polymers
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Lithium Niobate
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Our choice organic-inorganic material
mineral network
(sol-gel)gt

• Reticulation

organic network

• Polymerization

(UV) gt
Index change to write optical circuits
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Multimode interference devices
Multimode interference appears when exciting a
large guide, where each mode has its propagation
speed
Photograph of the outputs of a 1 x 32 power
divider
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Wavelength Division Multiple access
WDM made with our organic-mineral technology

• Two Multimode interference devices
• a splitter in input,
• a combiner in ouput

An array of single mode guides to build a set of
phases depending on the wavelength

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New approach to share the optical bandwidth
Code division multiple access (C.D.M.A.)
Radio frequency CDMA is used in third generation
mobile telephony (UMTS)
Optical CDMA

• Optical make coders and decoders

• Difficult interception appears as noise when
  code is unknown

•  soft  division versus WDMA

• Can maximize the number of users

• Can use non coherent sources (super LED, EDFA).

Several variants
Various implementations

• time CDMA with unipolar codes (Salehi)
• time CDMA with bipolar (phase) codes
  (Salehi-Wiener)
• spectral encoding (Nguyen, Zacarrin, Kavehrad)
• spectral with synchronizing pulse (Lam)
• fast frequency hopping (Rusch)

• array of fibers,
• array of MachZehnders,
• free space gratings

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Basics of CDMA
Each symbol  1  or  0  is coded as a sequence
of  chips  (time CDMA) or as a spectrum
(wavelength CDMA)
Message A 1,0,1gt
Message B 1,1,0gt
coded CBCB-CB
Transmitted
Sum of coded
signals A B C
A -decoding correlation with
(Transmitted CA)
Low pass filtering (time CDMA)
C

A
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Transmitter implementation
Message A
broad
M
M
Couplergt
spectrum "1"
M
M
band
I
I
Source
Other messages

• The WDM makes the spectral encoding. Input
  switching code switching.

• Non coherent source (such as E-TEK BLS 1300
  bandwidth50 nm).

• Gap between spectrum wavelength components,
  depending on symbol rate.

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Decoder receiver
M
M
Couplergt
Balanced photo-diodes
M
M
spectrum "1"
I
I
The sum of other codes yield balanced detection
Orthogonal codes

• Unipolar codes (Salehi) for time CDMA time
  distribution of a few short pulses gt few users

• Hadamard Walsh codes generated with Hadamard
  matrix, null cross correlation, can t be used in
  time CDMA for synchronisation (autocorrelation
  too high).

• m-sequences generated as random sequence, quasi
  orthogonality, allows theoretically a great
  number of users

• Gold codes combination of codes from
  m-sequences.

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Conclusion

• Organic-mineral technology has many qualities
  low cost, simple process, versatility...

• Index change (to write optical circuits) is
  directly and simply created by UV polymerisation,
  adjustable up to 0.03

gt Multiple access to the optical link

• Wavelength division multiplexing (WDMs),
• Code division multiplexing (CDM

• Visit our web site

http//www.cem2.univ-montp2.fr/moreau/