Printable Optical Filters for Visible Optical Communications

doi:10.4236/opj.2013.32B033

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Optics and Photonics Journal, 2013, 3, 136-138

doi:10.4236/opj.2013.32B033 Published Online June 2013 (http://www.scirp.org/journal/opj)

Printable Optical Filters for Visible Optical

Communications

P. S. André1,2, L. Nero1,3, Vânia T. Freitas2,4, M. S. Relvas2, R. A. S. Ferreira2,4

1Instituto de Telecomunicações, University of Aveiro, 3810-193 A v e i ro, Port ugal

2Physic Depar tment, U niversity of Aveiro, 3810-193 Aveiro, Portugal

3Electronics and Telecommunications Department, 3810-193 Avei ro, Por tugal

4CICECO, University of Aveiro, 3810-193 Aveiro, Portugal

Email: [email protected]

Received 2013

ABSTRACT

The design, production and characterization of tailored printable optical filters for visible optical communications are

demonstrated. As result, the average color difference between the specified and the produced filters is 32.6, quantified

in terms of CIELAB coordinates.

Keywords: Free-space Optical Communication; Wavelen gth Filterin g Devices

1. Introduction

Visible Light Communication (VLC) is a latest technique

in the field of wirele ss commu nications. T his is a “Gree n”

and energy-efficient emerging area, being developed by

several researcher groups seeking high bandwidth, high

sec urity, a nd frie ndly co mmun icatio n networ ks usi ng visi-

ble light instead of radio-frequ enc y or microwave signals.

Previous studies have shown that it is possible to

achieve a bandwidth of 500 Mbps [1]. The implementa-

tion of VLC systems using white light emission from

commercial Light Emission Diodes (LED) was initial

proposed by Komine and Nakagawa in 2004 [2]. The

utilization of LED sources opens a window of opportu-

nity for wavelength division multiplexing (WDM) [3].

However, the implementation of this solution requires

cost effective optical filtering devices. Despite the com-

mercial interest of the VLC technique, few works have

been devoted to the subject [4].

In this work we propose the design of novel optical

filters i nk-jet printed in transparencies as a low cost solu-

tion for the large scale implementation of WDM VLC

systems.

2. Spectral Design

The development of the commercial inkjet printers opens

the possibility to create tailored high dynamic range opt-

ical filters. These printers are based on a subtractive col-

or model, usually the CMYK model, which refers the 4

primary color used for printing, namely Cyan (C), Ma-

genta (M), Yellow (Y) and blacK (K). For an accurate

filter design it is essential a device color model that pro-

duces an estimate of the output characteristics for each

combination of input parameters, typically performed by

the printer color management system. Since we are in-

terested in transmission optical filters printed in transpa-

rent substrates, the Murray-Davies model can be used,

considering the spectral transmittance of the Neugebauer

primaries and the Demichel equations [5]. However, the

printing and the measurement of the Neugebauer prima-

ries is impracticable for commercial inkjet systems. Oth-

er proposed approach is based on the principal compo-

nent a na l yse s b ut r e qui ri n g a hig h c o mp uta ti onal c a lculus

to obtained the final transfer function [6]. Therefore, we

have implemented a distinct color model based on the

Murray-Davies, but using the CM YK pri maries.

In this approach, the filter average transmittance, T(λ),

is given by:

(1)

where Tj(λ) refers to the spectral transmittance for each

primary (CMYK), Pj is the p rimary intensit y value (fro m

0 to 100) and Tsubstrate(λ) is the substrate spectral trans-

mittance.

The 4 primary colors were printed in a BASF inkjet

transparency with 200 µm thickness, using an HP8100

inkjet printer. The spectral transmittance of each primary

was measured using a dual-beam spectrometer Lambda

950, (Perkin-Elmer) with a 150 mm diameter Spectralon

integrating sphere. These results were incorporated in

P. S. ANDRÉ ET AL.

137

equation 1 and used in an optimization routine, in order

to estimate the primaries intensity values that produce a

specific transmittance spectra. The optimization routine

was implanted in Matlab and was based in the Leven-

berg-Marquardt algorithm.

3. Implementation and Experimental Results

For the test of this procedure a specific scenery was con-

sidered [4], using three optical filters with distinct fea-

tures, in particular: band pass centered at i) 450 nm with

30 nm bandwidth (Blue) and at ii) 516 nm with 80 nm

bandwidth (Green) and iii) a high wavelength pass filter

with a transition edge at 586 nm (Red). The minimization

routine was applied to these spectral profiles, in order to

print sample substrates usi ng the above mentioned inkjet

printer. The transmittance spectra of these samples were

measured. Figure 1 shows the transmittance spectra for

the 3 optical filters termed as Red, Green and Blue. The

inset in Figure 1 illustrates the samples color.

In order to visualize the color difference between the

specified color and the measured one a uniform chroma-

ticity scale color space CIE (u’,v’) chromaticity diagram

was built using D65 illuminant and a 2º standard observ-

er, Figure 2.

The color difference between the specified one and the

obtained filter transfer function was further quantified

using the CIE (L*,a*,b*) color space (CIELAB, for the

D65 illuminant and the 2º standard observer). The meas-

ured (subscript m) and specified (subscript s) transmit-

tance spectra were quantified in terms of the parameters

L, a* and b* and the color difference obtained from:

(2)

The obtained color difference was 32, 31 and 35 for

the Red, Blue and Green filters, respectively, resulting in

380 414 448 482 516 550 584618 652 686 720

0.1

G reen

Blue

Red

Transmittance

Wavelength (nm)

Figure 1. Transmittance spectra for the 3 optical filters

designated as Red (R), Green (G) and Blue (B). The insets

show the color appearance for the R, G and B fi lters.

Figure 2. CIE (u’,v’) chromaticity diagram color for the

specified (open symbols) and measured (solid symbols)

optical fi lters transfer functions.

an average value of 32.6, which corresponds to a devia-

tion of 6.8%. This color difference between the measured

and specified filters can by relate to the limited color

Garmout of the inkjet printers. Nevertheless, the small

value for the color mismatch (6.8%) demonstrates that it

is possible to attain a tailored spectral response suitable

for the impleme ntation of V L C WDM syste ms.

4. Conclusions

We have demonstrated the production feasibility of tai-

lored printer optical filters. The filters transfer function

was optimized using a color model based on the Murray-

Davies, using the CMYK primaries. The average color

difference between the specified and produced filters is

32.6, quantified in terms of CIELAB coordinates, which

is a promising indicator about the potential of this low

cost solution for visible free space optical communica-

tions.

5. Acknowledgements

The financial support of “Scientific and technological

collaboration Portugal/China 2010/2012. Proc.0 441.00”

is gratefull y ac knowledged.

REFERENCES

[1] W.-Y. Li n , C .-Y. Chen, H.-H. Lu , C .-H. Chang, Y.-P. Lin,

H.-C. Lin and H.-W. Wu, “10m/500Mbps WDM Visible

Light Communication Systems” Optics Express, Vol. 20,

2012, pp . 9919-9924.

[2] T. Ko mine an d M. Nakagawa, “F u nd amental Analysis for

Visible Light Communication System Using LED

Lights,” IEEE Transactions on Consumer Electronics,

Vol. 50, 2004, pp. 100-107.

doi:10.1109/TCE.2004.1277847

P. S. ANDRÉ ET AL.

138

[3] K.Y. Cui , G. Chen, Q.F. He and Z.Y. X u, “ Ind oo r Optical

Wireless Communication by Ultraviolet and Visible

Light,”Proceedings of SPIE 7091, 2009, p. 709106.

[4] M. S. Uddin, J. S. Cha, J. Y. Kim and Y. M. Jang, “Mi ti-

gation Technique for Receiver Performance Variation of

Multi-Color Channels in Visible Light Communication”,

Vol. 11, 2011, pp. 61 31-6144.

doi:10.3390/s110606131

[5] I. A mid r or and R. D. Hersch, “Neugebauer an d Demichel:

Dependence and Independence in N-Screen Superposi-

tions for Colour Printing,” Color Research & Application

Vol. 25, 2000, pp. 267-277.

doi:10.1002/1520-6378(200008)25:4<267::AID-COL7>3

.0.CO;2-M

[6] J. McElvaina, J. M illera and E. Jin, “Spectral Printer

Modeling for Transparency Media: Toward High Dy-

namic Range Scene Reproduction”, Proceedings of SPIE,

Vol. 7241, 20 09, pp. 72 41 0U -1.

doi:10.1117/12.806123