High-resolution thin guest-host micropolarizer arrays for visible imaging polarimetry

High-resolution thin “guest-host”micropolarizer arrays for visible

imaging polarimetry

Xiaojin Zhao,1,∗ Farid Boussaid,2 Amine Bermak,1

and Vladimir G. Chigrinov1

1Department of Electronic and Computer Engineering, Hong Kong University of Science &Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China

2School of Electrical, Electronic and Computer Engineering, University of Western Australia35 Stirling Highway, Crawley WA 6009, Perth, Australia

*[email protected]

Abstract: We report a micropolarizer array technology exploiting“guest-host” interactions in liquid crystals for visible imaging polarime-try. We demonstrate high resolution thin micropolarizer arrays with a 5μm × 5 μm pixel pitch and a thickness of 0.95 μm. With the “host”nematic liquid crystal molecules photo-aligned by sulfonic azo-dye SD1,we report averaged major principal transmittance, polarization efficiencyand order parameter of 80.3%, 0.863 and 0.848, respectively across the400 nm − 700 nm visible spectrum range. The proposed fabricationtechnology completely removes the need for any selective etching duringthe fabrication/integration process of the micropolarizer array. Fully CMOScompatible, it is simple and cost-effective, requiring only spin-coatingfollowed by a single ultraviolet-exposure through a “photoalignment mas-ter”. This makes it well suited to low cost polarization imaging applications.

© 2011 Optical Society of America

OCIS codes: (110.5405) Polarimetric imaging; (120.5410) Polarimetry; (160.5335) Photosen-sitive materials; (230.5440) Polarization-sensitive devices.

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J. 2, 566–576 (2002).2. J. S. Tyo, D. L. Goldstein, D. B. Chenault, and J. A. Shaw, “Review of passive imaging polarimetry for remote

sensing applications,” Appl. Opt. 45, 5453–5469 (2006).3. J. Guo and D. Brady, “Fabrication of thin-film micropolarizer arrays for visible imaging polarimetry,” Appl. Opt.

39, 1486–1492 (2000).4. V. Gruev, A. Ortu, N. Lazarus, J. Van de Spiegel, and N. Engheta, “Fabrication of a Dual-Tier Thin Film Micro

Polarization Array,” Opt. Express 15, 4994–5007 (2007).5. V. Gruev, J. Van de Spiegel, and N. Engheta, “Dual-tier thin film polymer polarization imaging sensor,” Opt.

Express 18, 19292–19303 (2010).6. M. Momeni and A. H. Titus, “An Analog VLSI Chip Emulating Polarization Vision of Octopus Retina,” IEEE

Trans. Neur. Netw. 17, 222–232 (2006).7. C. K. Harnett and H. G. Craighead, “Liquid-crystal micropolarizer array for polarization-difference imaging,”

Appl. Opt. 41, 1291–1296 (2002).8. V. Gruev, R. Perkins, and T. York, “CCD polarization imaging sensor with aluminum nanowire optical filters,”

Opt. Express 18, 19087–19094 (2010).9. X. Zhao, A. Bermak, F. Boussaid, T. Du, and V. G. Chigrinov, “High-resolution photo-aligned liquid-crystal

micropolarizer array for polarization imaging in visible spectrum,” Opt. Lett. 34, 3619-3621 (2009).

#139737 - $15.00 USD Received 20 Dec 2010; revised 16 Feb 2011; accepted 28 Feb 2011; published 10 Mar 2011(C) 2011 OSA 14 March 2011 / Vol. 19, No. 6 / OPTICS EXPRESS 5565

10. T. Tokuda, S. Sato, H. Yamada, K. Sasagawa, and J. Ohta, “Polarisation-analysing CMOS photosensor withmonolithically embedded wire grid polariser,” Electron. Lett. 45, 228–230 (2009).

11. http://www.moxtek.com/templates/moxtek/pdf/datasheets/Pix-Polarizer-Data-Sheet.pdf12. M. Guillaumee, L. A. Dunbar, Ch. Santschi, E. Grenet, R. Eckert, O. J. F. Martin, and R. P. Stanley, “Polarization

sensitive silicon photodiodes using nanostructured metallic grids,” Appl. Phys. Lett. 94, 193503 (2009).13. X. Zhao, A. Bermak, F. Boussaid and V. G. Chigrinov, “Liquid-crystal micropolarimeter array for full Stokes

polarization imaging in visible spectrum,” Opt. Express 18, 17776-17787 (2010).14. D. Matsunaga, T. Tamaki, H. Akiyama, and K. Ichimura, “Photofabrication of Micro-Patterned Polarizing Ele-

ments for Stereoscopic Displays,” Adv. Mater. 14, 1477–1480 (2002).15. X. Zhao, F. Boussaid, A. Bermak, and V. G. Chigrinov, “Thin Photo-Patterned Micropolarizer Array for CMOS

Image Sensors,” IEEE Photon. Technol. Lett. 21, 805–807 (2009).16. G. H. Heilmeier and L. A. Zanoni, “Guest-Host Interactions in Nematic Liquid Crystals: A New Electro-Optic

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Polymer Liquid Crystal and Application to Linear Polarizer,” Chem. Lett. 34, 558–559 (2005).19. E. Peeters, J. Lub, Jan A. M. Steenbakkers, and D. J. Broer, “High-Contrast Thin-Film Polarizers by Photo-

Crosslinking of Smectic Guest-Host Systems,” Adv. Mater. 18, 2412–2417 (2006).20. D. Goldstein, Polarized Light (Marcel Dekker, New York, 2003).21. B. M. Ratliff, C. F. LaCasse, and J. S. Tyo, “Interpolation strategies for reducing IFOV artifacts in microgrid

polarimeter imagery,” Opt. Express 17, 9112–9125 (2009).22. J. S. Tyo, “Optimum linear combination strategy for an N-channel polarization-sensitive imaging or vision sys-

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with integrated microgrid polarimeters,” Opt. Lett. 34, 3187–3189 (2009).

1. Introduction

The integration of a micropolarizer array (i.e. a mosaic of micron-scale polarizer elements ofdifferent orientations) over the pixel array of an image sensor enables the concept of a low costsingle-chip polarization camera capable of capturing, in a single frame, the polarimetric infor-mation of a scene [1, 2]. A number of micropolarizer array implementations have been demon-strated for image sensors. Examples include patterned dichroic films such as polyvinyl alcohol(PVA) [3–5], birefringent YVO4 crystal covered by patterned aluminum films [6], multiple-domain liquid crystal (LC) with micro-patterned alignment layers [7], and nanometer-scalemetal wire-grids [8, 10, 11]. In each case, selective etching was used to pattern micropolarizerelements at the pixel pitch. The complexity of the selective etching process grows substan-tially with the number of patterned microdomains (i.e. micropolarizer element orientations) inthe micropolarizer array. Furthermore, to operate in the visible range, commercially availablewire-grid polarizers need to exhibit a grid pitch much smaller than the incident wavelength (i.e.less than 100 nm) [12]. Such requirements are not compatible with standard ultraviolet (UV)lithography. As a result, highly specialized equipment is required to enable advanced lithog-raphy. In addition, because wire-grid polarizers are made of delicate thin nano-wires, they arevery fragile and can be easily damaged by standard assembly processes. The cost associatedto the above complex processes is too prohibitive for the envisioned low cost complementarymetal-oxide-semiconductor (CMOS) polarization camera applications.

To completely remove the need for complex/expensive processes, we proposed to use LCphotoalignment techniques to fabricate micropolarizer arrays capable of extracting the firsttwo Stokes parameters [9] or all four Stokes parameters [13]. These LC-based micropolariz-ing devices need to exhibit relatively large thicknesses (5 μm − 10 μm) in order to satisfythe Mauguin condition [9] or achieve enough phase retardation [13]. This leads to not onlyreduced light collection angles but also increased cross-talk between adjacent photo-sensingpixels, especially when their size is scaled down to 10 μm and below [3].

These issues can be addressed by fabricating thin micropolarizer arrays using photosensitivedichroic dyes [14,15]. In [14], an LC photoalignment technique was adopted to selectively align


a lyotropic liquid crystal (LLC) dye. This implementation can only achieve a spatial resolutionof 70 μm with a polyamide having a dimethylaminoazobenzene substituent (MNC10-PAM) asthe photoalignment material. In addition, it suffers from severe spindle-like craters (2 μm inwidth, 3 μm − 4 μm in length) and careful selection of the surfactants is necessary to suppressthese defects, whose size can be comparable to the pixel pitch. In [15], the micropolarizer arraywas fabricated with a spin-coated photosensitive azo-dye-1 (AD1) as the polarizing film. Thismaterial exhibits a strong dichroism after sufficient exposure to linearly polarized ultraviolet(UV) light. The rod-like molecules of a spin-coated AD1 film can be oriented with their longmolecular axes perpendicular to the orientation of the projected polarized UV light. However,the orientation degree of AD1 molecules is a function of the exposure energy and saturatesafter prolonged UV exposure. As a result, the UV-patterned polymer AD1 film exhibits limitedmajor principal transmittance, polarization efficiency and order parameter [15].

To improve both the spatial resolution of the micropolarizer and its optical performance, thispaper proposes to exploit “guest-host” interactions [16, 17] in nematic liquid crystals (NLCs).The latter consist of rod-like organic molecules, whose regional ordering is characterized bythe parallel alignment of molecules, along their long molecular axes. A well-known property ofNLCs is that the orientation of the molecules can be controlled with an external electric field.Heilmeier et al. discovered that by controlling the molecular orientation of a nematic “host”material, the properties of the “guest” materials mixed with the nematic “host” can be controlled[16]. This property was exploited in [17], with LC molecules used as the “host” and polarizationdichroic dye molecules dissolved in the LC used as the “guest”. When an external tunableelectric field is added to the LC cell with its direction perpendicular to the LC substrates, the“host” LC molecules are reoriented with their molecular axes having an angle ranging from 0◦to 90◦ with respect to the LC substrates. The “guest” dichroic dye molecules, mixed with the LCmolecules, can thus be cooperatively aligned and the transmittance of input linearly polarizedlight passing the LC cell can be tuned by changing the electric field magnitude. This interactionenables electrically-tunable brightness and was first introduced for liquid crystal display (LCD)applications [17]. Subsequently, it was extended to the fabrication of coatable high quality thin-film patterned linear polarizers used for binocular disparity 3D stereoscopic displays [18, 19].In the latter, instead of applying an electric field [16, 17], linearly polarized UV light [18] orLC alignment layers [19] were exploited to provide planar alignment (i.e. parallel to the LCsubstrates) of the “host” LC molecules. With the “guest” dichroic dye molecules cooperativelyaligned by their LC “host”, the device is optically equivalent to a linear polarizer [18, 19]. In[18], reported peak polarization efficiency and order parameter are limited to 0.98 and 0.82, at awavelength of 584 nm. In addition, the “guest” dichroic dye (N256 from Hayashibara Biochem.Labs. Inc.) exhibits poor absorbance in the blue and red regions of the visible spectrum. In [19],the patterned micropolarizer array is implemented with selective polymerization of the LC“host” on top of a rubbed LC alignment layer. The latter can inherently provide micropolarizerswith only one local polarization direction. Moreover, the fabricated micropolarizer array in [19]exhibits a relatively large thickness (5 μm) and the reported spatial resolution is limited to 100μm.

In this paper, a high-resolution submicron thin “guest-host” micropolarizer array is presentedwith a sulfonic azo-dye SD1 as the LC photoalignment material to photo-align the polymeriz-able NLC “host” material. A pixel pitch of 5 μm × 5 μm is achieved with improved majorprincipal transmittance, polarization efficiency and order parameter. In addition, a patternedUV-regime metal-wire-grid polarizer is exploited as a “photoalignment master” to enable aone-step photolithography of the NLC layer. The proposed high resolution micropolarizer arraytechnology is simple, cost-effective and removes alignment errors associated with multi-maskUV-exposure steps. This paper is organized as follows. Section 2 describes the design and fab-


rication process flow of the “guest-host” micropolarizer array. Experimental characterizationresults are reported and discussed in Section 3. Finally, a conclusion is drawn in Section 4.

2. “Guest-host” micropolarizer array

In this paper, we propose a UV-sensitive sulfonic azo-dye SD1 film-based non-contact pho-toalignment technique to fabricate high-resolution thin “guest-host” micropolarizer arrays. Asdepicted in Fig. 1 (A), a substrate, representing the image sensor, is first spin-coated with thisSD1 film. After subsequent irradiation by linearly polarized UV light, photoalignment of SD1molecules occurs [Fig. 1 (B)] with the SD1’s long molecular axes perpendicular to the polar-ization direction of projected linearly polarized UV light. The “guest-host” mixture of dichroicdye and NLC is then spin-coated on top of the SD1 film, which will act as an alignment layerfor the NLC “host” molecules and the dichroic dye “guest” molecules. Fig. 1 (C) depicts thisreorientation process with “host” and “guest” molecules aligned with SD1 molecules.

Linearly polarized UV light“Host” NLC

Linearly polarized UV light“Guest” dichroic Host NLC

l lSD1Guest” dichroicd l l moleculesSD1

l ldye molecules

molecules

S i t d SD1 fil Ph t li d SD1 l l S i t d “ t h t” i tSpin-coated SD1 film Photo-aligned SD1 molecules Spin-coated “guest-host” mixture

(A) (B) (C)(A) (B) (C)

Fig. 1. Photoalignment of “host” NLC molecules and “guest” dichroic dye molecules.

To demonstrate the proposed “guest-host” technology, we fabricated micropolarizer arrayscapable of extracting full partial linear polarization information [20]. Each fabricated micropo-larizer array exhibits a 2×2 pattern comprising 0◦, 90◦, 45◦ and −45◦ micropolarizers (Fig. 2).Here, each pixel will look through either a micropolarizer of 0◦, 90◦, 45◦ or −45◦ (Fig. 2). Asa result, a single intensity value is available per pixel. The three other missing intensity valuesare recovered by examining the intensity values of neighboring pixels. A 2×2 (or larger) con-volution kernel can be applied to estimate the first three Stokes parameters at each point. Thisapproach trades off spatial resolution to allow for polarization measurements to be made simul-taneously during a single image capture. In essence, this process is similar to color filter arrayinterpolation or demosaicing. Ratliff et al. and Tyo et al. have recently reviewed and analyzedpossible interpolation strategies for polarimetry [21–23].

To enable the optical characterization of the fabricated micropolarizer array, a transparentglass substrate was used instead of the silicon-based opaque CMOS image sensor substrate.The detailed fabrication steps of the “guest-host” micropolarizer array, shown in Fig. 2, can besummarized as follows:

1. Organic contaminants were removed from the surface of the transparent glass substrate,using an ultraviolet-ozone (UVO) cleaning machine (Jelight 144AX).

2. An SD1 solution was then spin-coated onto the glass at 800 rpm for 10 s then 3000rmp for 40 s. In order to eliminate particle impurities, the solution of SD1 in dimethyl-formamide (DMF) with a concentration of 1% by weight was filtered before the spin-coating.


Glasssubstrate

spin coat NLCphotoalignment material

(800 rpm, 10 s, then 3000 rpm, 40 s)

110 °C bake20 min

UVO clean 20 min

0° reference

90° reference

One-step UV photoalignment

UV lightphotoalignmentmaster

Glasssubstrate

Glasssubstrate

photo-aligned SD1

Glasssubstrate

Glasssubstrate

spin coat “guest-host” mixture

(800 rpm, 5 s, then 3000 rpm, 30 s)

NLC “host”polymerization

photoalignment master (from Moxtek Inc.)(i.e. patterned UV metal-wire-grid polarizer)

5 m

0° linearmicropolarizer

90° linear micropolarizer



Adopted micropolarizer array pattern

Fig. 2. Proposed “guest-host” micropolarizer array fabrication process flow and adoptedpattern.

3. The glass substrate was then baked at 110 ºC for 20 min to remove the remaining solventand strengthen the adhesion of the SD1 material to the substrate.

4. The spin-coated SD1 layer on the glass substrate was subsequently photo-aligned withthe customized “photoalignment master” applied (Fig. 2), which is actually a patternedUV-regime metal-wire-grid polarizer from Moxtek Inc. This “photoalignment master”,featuring 5 μm × 5 μm pixel pitch, enables one-step UV-photoalignment of the SD1layer making the fabrication process simple, cost-effective and high resolution with nomisalignment errors. The UV-exposure duration was 15 min and the UV light intensityat 365 nm was around 5.6 mW/cm2. As a result, SD1 molecules were photo-aligned indifferent microdomains along 0◦, 90◦, 45◦ and −45◦, respectively.

5. After patterning the NLC photoalignment SD1 layer, a mixture of the dichroic dye so-lution and the NLC solution (with a mass ratio of 1:1) was spin-coated on top of thepatterned SD1 layer at a speed of 800 rpm for 5 s then 3000 rpm for 30 s.

6. Next, the substrate with the spin-coated “guest-host” mixture was baked at 50 ºC for 3min to eliminate the solvents.

7. Finally, a UV light with an intensity of 2 mW/cm2 and a wavelength of 254 nm, which isnot within SD1’s sensitive spectrum and cannot thus reorient SD1 molecules, is appliedfor 3 min to polymerize the NLC “host” material. This last step ensures stability andprotection against changing environmental conditions.


3. Experimental results and discussion

In order to examine each micropolarizer domain, the fabricated “guest-host” micropolarizerarray sample was back-illuminated by the white light source of a microscope from OlympusCorp. (BH3-MJL). A broadband linear polarizer (from Moxtek Inc.) was inserted and rotatedbetween the white light source and the fabricated sample to provide four different polarizedinputs: 0◦ linearly polarized, 90◦ linearly polarized, 45◦ linearly polarized and −45◦ linearlypolarized. According to [20], the normalized Stokes parameters (S1/S0, S2/S0) of the four dif-ferent polarized inputs are (1, 0), (−1, 0), (0, 1) and (0, −1), respectively. Fig. 3 presentsthe sample’s microphotographs examined by a linear polarization analyzer and recorded bythe microscope’s camera system (MotionBLITZ© Cube2). With the microscope’s embeddedpolarization analyzer and lens system, the camera can record a 1280×1024 image of the fab-ricated micropolarizer array with a resolution as small as 1 μm. Note that 0◦, 90◦, 45◦ and−45◦ micropolarizers appear dark as expected when the input is 90◦, 0◦, −45◦ and 45◦ linearlypolarized, respectively.

5 m

Analyzer Analyzer

AnalyzerAnalyzer

(A) (B)

(C) (D)

Fig. 3. Microphotographs of the fabricated “guest-host” micropolarizer array, inspected bya linear polarization analyzer along the following orientations: (A) 0 degree; (B) 90 degree;(C) 45 degree; (D) −45 degree.

In addition, the micropolarizer pitch is shown to be 5 μm × 5 μm, which matches state-of-the-art commercially available wire-grid polarizers [11]. It is important to note that thisresolution is not an indication of the resolution limit of the proposed micropolarizer fabricationtechnology but only the result of our choice of readily available general masks. The resolu-tion limit of the proposed micropolarizer fabrication technology is set by the resolution of theadopted photolithography process. This performance enables the integration of the fabricatedmicropolarizer array with mainstream commercial CMOS image sensors, whose photo-sensingpixel size is usually less than 10 μm. The overall “guest-host” micropolarizer array thicknessincluding the SD1 photoalignment layer was measured by a surface profiler (Tencor P-10) andfound to be 0.95 μm. Compared to PVA [3–5] and crystal [6] based micropolarizer arrays, theproposed technology enables a reduction of the micropolarizer thickness by a factor of 20 to


887, respectively. Wire-grid polarizers provide the thinnest solution with less than 100 nm re-ported [11]. However, the latter rely on a far more complex and costly process, with multiplelithography and etching steps required. Because wire-grid polarizers are parallel arrangementsof delicate thin aluminium nano-wires, they are fragile and can thus be easily damaged by stan-dard assembly processes. This adds significant complexity/cost in the handling of the wire-gridpolarizers during assembly.

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Fig. 4. Spectral measurement results: (A) the major and minor principal transmittances T‖,T⊥; (B) polarization efficiency PE.

Furthermore, the fabricated micropolarizer array was characterized by measuring the fourimportant figures of merit: transmittances (T‖, T⊥) and absorbances (A‖, A⊥). Measurementswere performed using a polarization state generator (PSG) comprising a mini deuterium halo-gen light source (DT-Mini-2-GS from Mikropack GmbH) and a broadband linear polarizer(from Moxtek Inc.). This PSG can provide linearly polarized input light with wavelengths rang-ing from 400 nm to 700 nm. Since the micropolarizer pitch is in the micrometer scale, whichis much smaller than the PSG’s laser beam, we fabricated unpatterned “guest-host” linear po-larizer samples (2.5 cm × 2.0 cm) together with the micropolarizer arrays to cover the PSG’slaser beam and enable the characterization of the fabricated micropolarizers. Fig. 4 (A) showsthe spectral measurement results of both the major and the minor principal transmittances T‖,T⊥. The major principal transmittance is seen to range from 71.9% (551 nm) to 96.8% (699nm) with an average of 80.3% across the whole visible spectrum (i.e. from 400 nm to 700 nm).Another important figure of merit is the polarization efficiency (PE), defined as [19]:

PE =

√T‖ −T⊥T‖+T⊥

×100% (1)

The average PE across the whole visible spectrum was found to be 0.863 with the maximum PEequal to 0.996 at a wavelength of 545 nm and the minimum PE equal to 0.114 at a wavelengthof 699 nm [Fig. 4 (B)]. Moreover, the two absorbances A⊥, A‖ are reported in Fig. 5 (A). Theorder parameter S, defined as the ratio of (A‖ −A⊥) and (A‖ + 2A⊥) [19], is calculated andplotted in Fig. 5 (B) with an average of 0.848 across the whole visible spectrum. The maximumand minimum order parameters are 0.872 (623 nm) and 0.699 (699 nm), respectively.

Comparing this optical performance against previously reported micropolarizer arrays is dif-ficult because figures of merit (e.g. PE, S, transmittance) are a function of the wavelengthand only their peak values are typically reported in the literature. As a result, it is very dif-ficult to directly compare some of our results with prior art, without access to the actual raw


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Fig. 5. Spectral measurement results: (A) absorbances A⊥, A‖ corresponding to the majorand minor principal transmittances T‖, T⊥; (B) order parameter S.

measurements and without considering the targeted application, for which the micropolarizerarrays were optimized [18,19]. Nevertheless, we can make the following observations in regardto previously reported photosensitive dichroic dyes. In [18], the N256 dichroic dye exhibitspoorer absorbance in the blue and red regions of the visible spectrum, with a peak polarizationefficiency and order parameter limited to 0.98 and 0.82, respectively, at a wavelength of 584nm. In [19], only an averaged order parameter of 0.94 is reported. However, this relatively highorder parameter is shown to decrease dramatically down to 0.83 with the polymerization of the“host” LC material [19]. In addition, the covered spectrum ranges from 450 nm to 550 nm,which corresponds to only about one third of the whole visible spectrum [19]. In this paper, thespectrum band, for which PE exceeds 0.90, ranges from 417 nm to 635 nm. This correspondsto 73% of the whole visible spectrum. This enables high-quality monochromatic or achromaticpolarization image sensing applications. Ongoing efforts are focusing on the development andsynthesis of dichroic dyes, which are more sensitive to the visible spectrum towards the UVand infrared (IR) ends. Compared to state-of-the art visible range wire-grid polarizers [11], theproposed micropolarizer technology boasts similar performance in terms of pixel size or trans-mittance. However, it does not perform as well in terms of polarization efficiency (99.6% versus99.8%) or layer thickness (950 nm versus 100 nm). Nevertheless, given the proposed fabricationtechnique drastically simplifies the fabrication/integration process (e.g. spin-coating followedby a one step-UV lithography with no etching) of the micropolarizer array, it constitutes an at-tractive trade-off between performance and cost, making it well suited for low cost polarizationimaging applications.

4. Conclusion

We have fabricated and characterized a high-resolution “guest-host” micropolarizer array withdichroic dye as the “guest” and polymerizable NLC as the “host”. Experimental results demon-strate that micropolarizer arrays exploiting “guest-host” interactions can offer higher resolution(5 μm × 5 μm pixel pitch), 0.95 μm thickness but also superior optical performance across thewhole visible spectrum, with averaged major principal transmittance, polarization efficiencyand order parameter of 80.3%, 0.863 and 0.848, respectively. This is achieved by controllingthe “guest” molecular orientation through the photoalignment of “host” molecules. The pro-posed non-contact micropolarizer array fabrication technology prevents mechanical damage,


electronic charge or contamination to the substrate. Furthermore, it is simple and cost-effective,requiring only a single UV-exposure through a “photoalignment master”. It is also fully com-patible with standard CMOS process, enabling the integration of a “guest-host” micropolarizerarray over a CMOS image sensor to realize the concept of a low cost single-chip polarizationcamera.

Acknowledgments

This work was supported by the Research Grant Council of Hong Kong SAR, P. R. China (Ref.GRF610608).


High-resolution thin guest-host micropolarizer arrays for visible imaging polarimetry

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