OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 8 — Apr. 11, 2011
  • pp: 7468–7479
« Show journal navigation

Adjustable hybrid diffractive/refractive achromatic lens

Pouria Valley, Nickolaos Savidis, Jim Schwiegerling, Mohammad Reza Dodge, Gholam Peyman, and N. Peyghambarian  »View Author Affiliations


Optics Express, Vol. 19, Issue 8, pp. 7468-7479 (2011)
http://dx.doi.org/10.1364/OE.19.007468


View Full Text Article

Acrobat PDF (1104 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We demonstrate a variable focal length achromatic lens that consists of a flat liquid crystal diffractive lens and a pressure-controlled fluidic refractive lens. The diffractive lens is composed of a flat binary Fresnel zone structure and a thin liquid crystal layer, producing high efficiency and millisecond switching times while applying a low ac voltage input. The focusing power of the diffractive lens is adjusted by electrically modifying the sub-zones and re-establishing phase wrapping points. The refractive lens includes a fluid chamber with a flat glass surface and an opposing elastic polydimethylsiloxane (PDMS) membrane surface. Inserting fluid volume through a pump system into the clear aperture region alters the membrane curvature and adjusts the refractive lens’ focal position. Primary chromatic aberration is remarkably reduced through the coupling of the fluidic and diffractive lenses at selected focal lengths. Potential applications include miniature color imaging systems, medical and ophthalmic devices, or any design that utilizes variable focal length achromats.

© 2011 OSA

1. Introduction

A traditional achromatic lens or achromat corrects for primary chromatic aberration by matching the focal points of a red and a blue wavelength. The dispersion is reduced over the visible spectrum, however residual secondary chromatic aberration remains at the green wavelength. Achromatic doublets consist of a crown glass followed by a flint. The crown glass has a positive focal length with low dispersion while the flint has a negative power with high dispersion. The combination of these two glass disparities is designed to match the red and blue wavelengths to a common focus along the optical axis (z-axis) to eliminate primary chromatic aberration.

It is known that diffractive lenses have strong chromatic aberration [1

1. D. C. O'Shea, T. J. Suleski, A. D. Kathman, and D. W. Prather, Diffractive Optics: Design, Fabrication, and Test (SPIE Press Book, 2004).

]. We have previously reported on designing and demonstrating adjustable focus diffractive lenses using liquid crystal as the variable index medium [2

2. P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]

,3

3. P. Valley, M. Reza Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Nonmechanical bifocal zoom telescope,” Opt. Lett. 35(15), 2582–2584 (2010). [CrossRef] [PubMed]

]. In this paper, we present an adjustable liquid crystal diffractive lens and an adjustable pressure-controlled fluidic lens that in combination (Fig. 1
Fig. 1 Schematic of the hybrid liquid crystal diffractive lens and fluidic lens.
) minimizes primary chromatic aberration. Previously, discrete tunable liquid crystal diffractive lenses [2

2. P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]

6

6. B. E. Bagwell, D. V. Wick, R. Batchko, J. D. Mansell, T. Martinez, S. R. Restaino, D. M. Payne, J. Harriman, S. Serati, G. Sharp, and J. Schwiegerling, “Liquid crystal based active optics,” Proc. SPIE 6289, 628908, 628908-12 (2006). [CrossRef]

], continuous tunable liquid crystal refractive lenses [7

7. H. C. Lin and Y. H. Lin, “An electrically tunable focusing liquid crystal lens with a built-in planar polymeric lens,” Appl. Phys. Lett. 98(8), 083503 (2011). [CrossRef]

9

9. H. Ren, Y. H. Fan, S. Gauza, and S. T. Wu, “Tunable-focus flat liquid crystal spherical lens,” Appl. Phys. Lett. 84(23), 4789–4791 (2004). [CrossRef]

], and continuous tunable fluidic lenses [10

10. D. Y. Zhang, N. Justis, and Y. H. Lo, “Integrated fluidic adaptive zoom lens,” Opt. Lett. 29(24), 2855–2857 (2004). [CrossRef]

12

12. R. Marks, D. L. Mathine, G. Peyman, J. Schwiegerling, and N. Peyghambarian, “Adjustable fluidic lenses for ophthalmic corrections,” Opt. Lett. 34(4), 515–517 (2009). [CrossRef] [PubMed]

] with variable focal lengths were demonstrated individually. At each focal location chromatic aberration is observable when uncorrected. Chromatic aberration is greater in elements with larger dispersion, such as diffractive lenses, and becomes more significant for materials with lower Abbe numbers. Diffractive and holographic lenses have been proposed to replace the traditional achromatic doublets for fixed focal length designs [1

1. D. C. O'Shea, T. J. Suleski, A. D. Kathman, and D. W. Prather, Diffractive Optics: Design, Fabrication, and Test (SPIE Press Book, 2004).

,13

13. T. Stone and N. George, “Hybrid diffractive-refractive lenses and achromats,” Appl. Opt. 27(14), 2960–2971 (1988). [CrossRef] [PubMed]

]. More recently, a useful hybrid variable focal length fluidic/diffractive lens was demonstrated; however, the diffractive component applies a fixed focal length [14

14. G. Zhou, H. M. Leung, H. Yu, A. S. Kumar, and F. S. Chau, “Liquid tunable diffractive/refractive hybrid lens,” Opt. Lett. 34(18), 2793–2795 (2009). [CrossRef] [PubMed]

]. We have extended this work to include a variable focal length diffractive component. In effect, we have created a variable achromatic doublet with no moving parts.

Diffractive lenses have an Abbe number much smaller than their refractive counterparts [1

1. D. C. O'Shea, T. J. Suleski, A. D. Kathman, and D. W. Prather, Diffractive Optics: Design, Fabrication, and Test (SPIE Press Book, 2004).

]. The Abbe number of a diffractive lens is unique in that it is equal to -3.45, solely dependent upon the specified Fraunhofer d, F, C wavelengths, as given by Vdiffractive = λd / (λF - λC) [1

1. D. C. O'Shea, T. J. Suleski, A. D. Kathman, and D. W. Prather, Diffractive Optics: Design, Fabrication, and Test (SPIE Press Book, 2004).

,13

13. T. Stone and N. George, “Hybrid diffractive-refractive lenses and achromats,” Appl. Opt. 27(14), 2960–2971 (1988). [CrossRef] [PubMed]

]. The focal length of a Fresnel zone-based diffractive lens is given by f = r12 / (2 λ) where r1 is the radius of the first Fresnel zone and λ is the wavelength of the incident light [1

1. D. C. O'Shea, T. J. Suleski, A. D. Kathman, and D. W. Prather, Diffractive Optics: Design, Fabrication, and Test (SPIE Press Book, 2004).

]. Therefore, the focal length at any other wavelength λ, in nm, can be scaled by the design wavelength according to f (λ) = (555/ λ) fd where fd is the design focal length at 555 nm.

2. Liquid crystal diffractive lenses

We began by designing diffractive elements with known focal lengths and Abbe numbers. We developed two variable focal length diffractive lenses. Diffractive lens A possesses a design focal length of 1000 mm at λ = 555 nm with a clear aperture of 10 mm and eight binary phase quantization that results in a maximum diffraction efficiency of 94.9% in theory. Diffractive lens B possesses a design focal length of 400 mm at λ = 555 nm with a clear aperture of 6 mm and twelve levels of binary phase quantization that results in a maximum diffraction efficiency of 97.7% in theory. By properly shunting the electrodes, the diffractive lens A can provide focal lengths of 1000 mm, 500 mm, and 250 mm, and the diffractive lens B can provide 400 mm, 200 mm, 133 mm, 100 mm, and 67 mm focal lengths [2

2. P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]

,3

3. P. Valley, M. Reza Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Nonmechanical bifocal zoom telescope,” Opt. Lett. 35(15), 2582–2584 (2010). [CrossRef] [PubMed]

].

Desired phase profiles are achieved by shifting the effective refractive index of a nematic liquid crystal. The nematic liquid crystal is sandwiched between a flat Fresnel zone electrode substrate and a ground reference substrate, where both substrates contain a transparent and conductive Indium-Tin-Oxide (ITO) layer. To maintain the electrical isolation between the electrodes in the diffractive lens A, the odd-numbered and even-numbered electrodes are formed in two separate layers with an insulating layer of SiO2 in between [3

3. P. Valley, M. Reza Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Nonmechanical bifocal zoom telescope,” Opt. Lett. 35(15), 2582–2584 (2010). [CrossRef] [PubMed]

]. For the diffractive lens B, one-micron gaps are implemented as isolators between the electrodes that reduce the fabrication steps [2

2. P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]

]. The electrodes (or subzones) of the same counting index within each of the Fresnel zones are connected to bus bars through vias made in the insulating layer of SiO2.

Fabrication of our diffractive lenses involves a few steps of deposition, lithography and etching. Ion beam sputtering was the deposition method used to produce uniform films of around 150 nm thick. Then photo-lithography was carried out using a diluted S-1805 photoresist (from Rohm and Hoss) and Karl-Suss MA6 mask aligner. The patterns were then etched using the appropriate acids/etchants for each layer. After the micro-fabrication process, both the patterned electrodes and the reference substrates are spin-coated with a nylon alignment layer. The substrates are then baked at 115 °C, buffed unidirectionally, and put together in the anti-parallel geometry to provide a homogeneous molecular orientation for the liquid crystal. Glass fiber spacers are used in the cell assembly. The lens cell is filled with the liquid crystal (E7 from Merck) via the capillary action at a temperature above the clearing point (60°C) and cooled slowly to the room temperature. Finally, the cell is sealed and connected to drive electronics through a set of thin stranded wires.

Two resistive circuits with eight and twelve potentiometers drive the diffractive lenses. The resistances and the input voltage, hence the driving electric field across different Fresnel subzones, are adjusted to introduce the appropriate phase shift for the maximum diffraction efficiency. The voltages are applied simultaneously and are monotonically increasing from the first to the last subzone. The focal lengths are electronically switchable to fractions of the maximum design focal length in milliseconds. It is also possible to achieve negative focal lengths by reversing the order in which the voltages are applied to the diffractive lenses, thus reversing the slope of the phase profile [2

2. P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]

,3

3. P. Valley, M. Reza Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Nonmechanical bifocal zoom telescope,” Opt. Lett. 35(15), 2582–2584 (2010). [CrossRef] [PubMed]

].

3. Fluidic refractive lens

The refractive lens is a plano-convex singlet with a predetermined amount of fluid inserted into the lens chamber. During preparation, fluid is inserted in excess within the chamber as to induce a vacuum pressure to evacuate air. If the air is not evacuated then it is treated as a second index within the clear aperture, resulting in a drastic alteration of desired lens properties. Only the membrane curvature changes when fluid is pumped into the chamber since the frame is metal and the opposing side is transparent glass.

The deformable membrane layer is a moldable optically clear elastomer with uniform thickness. Fabrication of the deformable membrane involves a pre-backing process while the PDMS mixture is formulated within molds designed on a flat 5 λ glass surface. The mixture is deposited within the molds which are then stirred within a vacuum system as to remove the excess air within the PDMS. The thickness of the membrane depends on the amount of material deposited within each mold. After the air is evacuated, the PDMS is placed into an oven at 90° C for an hour. We then remove the PDMS and peel off the membrane layers, which have a designed thickness of approximately 30-120 microns [12

12. R. Marks, D. L. Mathine, G. Peyman, J. Schwiegerling, and N. Peyghambarian, “Adjustable fluidic lenses for ophthalmic corrections,” Opt. Lett. 34(4), 515–517 (2009). [CrossRef] [PubMed]

]. The membrane layers are removed with nylon tweezers and trimmed to remove excess material. Removal of excess material is necessary as to ensure a flat membrane to be clamped into the chamber.

The chamber is a metal frame which the membrane locks into, possessing a clear aperture within the center and flanges on its periphery. Control of the lens’ output shape is achieved by controlling the clear aperture’s opto-mechanical shape, where this clear aperture has a circular shape as to produce a rotationally symmetric fluidic lens. There is a retainer ring that has equal and opposite flanges relative to the metal frame. Through pressure, the membrane is applied onto the flat metal frame and the retainer ring locks the membrane onto the frame. This flat frame is then aligned and squeezed into a two part assembly, creating the singlet chamber. The chamber is then mounted onto a frame that has openings to place onto a rail. The chamber poses a single fluidic fitting that connects the fluid chamber to a syringe.

A syringe is placed into a pump system that alters the fluid output, permitting for control of the fluidic lens’ radius of curvature and focal length. The applied pump controllers operate at a maximum of 0.0125 ml / sec, an operation rate of 50 µl in 4 seconds. This corresponds to a focal shift of approximately 10 mm per 50 µl evacuation when there is high lens curvature, and a shift of approximately 50 to 100 mm per 50 µl evacuation. The boundary between high curvature and low curvature varies with the designed focal length. With our fluidic chamber, which was designed for an 80 mm base focal length with methanol, an evacuation of 150 µl defines our barrier between low curvature and high curvature. It is observed in Fig. 4
Fig. 4 Chromatic dispersion of the variable focal plano-convex lens alone applying methanol at the three test wavelengths when set for 80 mm focal length and higher.
as the approximate location in which the slope varies in the relative amount of fluid evacuated. Due to drastic fluid removal effects at flatter curvatures, it was opted to decrease the amount of fluid inserted or removed at higher radii of curvature. A plano-convex lens is developed over this region and only positive focal lengths are selectively outputted.

4. Methods and test results

As was previously stated we applied DI water, with known indices of refraction per wavelength, in identifying the fluidic lenses radius of curvature range. For a given amount of fluid in the lens, we measured the focal length at each of the three test wavelengths. The radius of curvature, r, of the lens surface was calculated using Ф = 1/f = (nair - nDI)/r, where Φ is the surface power and nair and nDI are the indices of refraction for air and DI water per index, respectively. It is noted that with the defined coordinate system the radius of curvatures are negative values as the vertex to the center propagates to the left; however, we are stating the values as definitions of magnitude as to alleviate the constraint of a coordinate system. The index of refraction for air is approximately one at all wavelengths and the index of refraction of DI water is known at each wavelength [16

16. M. Daimon and A. Masumura, “Measurement of the refractive index of distilled water from the near-infrared region to the ultraviolet region,” Appl. Opt. 46(18), 3811–3820 (2007). [CrossRef] [PubMed]

]. The focal length, f, of each measurement was equal to the back focal distance of the fluidic lens using the thin lens approximation. Each radius of curvature was calculated at red, green, and blue wavelengths and averaged to determine a single radius of curvature per fluid volume. The experiment was repeated as we increased the fluid volume in the lens by increments of 50µL.

To define the workable range for the fluidic lens we quantified the repeatability of outputting the radius of curvature. It was found that the average radius of curvature per fluid volume between the three wavelengths varied in accuracy of 0.02% to 0.88% for a radius of curvature from 20 to 100 mm. For DI water this corresponded to a focal length range of 60 mm to 300 mm. To clarify, a radius of curvature with an accuracy of 0.02% means that our lens accuracy for a radius of curvature at 20 mm was at 20 mm +/− 0.004 mm or with an accuracy of 0.88% the radius of curvature outputted at 20 mm +/− 0.176 mm. Similarly the radius of curvature range for our larger 100 mm varied from 100 mm +/− 0.02 mm to 100 mm +/− 0.88 mm respectively. It was found that the smaller radii of curvature actually observed a lower amount of inaccuracy. As we increase the amount of fluid we are reducing the lenses radius of curvature. This suggests that our caustic is not as long and more of the rays are focused in one location. What is occurring is that with a smaller radius of curvature we have almost no effect by the frame which allows for the shape of the membrane to be controlled by the fluid with almost no dependence on the opto-mechanical structure. With this higher control the smaller the radius of curvature the higher control of aberrations is observed.

With the focal length range approximated it was necessary to determine the proper fluid Abbe number to achromatize the focal lengths of the diffractive lens. On the left hand side of Table 1 are the diffractive lens values that would be required to be achromatized. Table 1 identifies which focal lengths are needed from the fluidic lens for each Abbe number to achieve achromitization with these designed diffractive lens powers. Our approximation showed that our fluidic lens will achieve focal lengths in the relative area of 50 mm or higher. Our experimental DI water has an Abbe number of 55. It is seen within the table that DI water would only achromatize the 1 D Diffractive lens with our fluidic lens, due to the constraints on the lenses radius of curvature. A fluid with an Abbe number of 15 would achromatize four of the diffractive lens’ focal lengths and an Abbe number of 10 would achromatize five focal lengths above 50 mm. Theoretically, a fluid with an Abbe number of 5, as observed from Table 1, would produce approximately all possible achromatic combinations from either diffractive lens developed here, since the greatest Diopter range achieved by the diffractive lenses is 15 D. Thus, finding a fluid with known indices of refraction to achieve a focal length as low as 50 mm and a characterized Abbe numbers from 5 to 15 offers the capability of illustrating a variable focal length achromat.

Methanol (Methyl alcohol) was chosen as the fluid for the fluidic lens due to its high dispersion value and non-reactivity with the PDMS membrane. Methanol has an Abbe number of 13.66 which achromatizes 5 of the diffractive lens focal lengths as is observed in Table 1 and is widely available as it is a cleaning agent. The desired focal length range to achromatize all of the diffractive lenses focal locations with the fluidic lens would be from 16.8 to 101.0 mm when coupled with diffractive lens B and from 63.14 to 252.6 mm when coupled with diffractive lens A. As was previously stated, the diffractive lens A provides focal lengths of 1000, 500, and 250 mm, and the diffractive lens B provides 400, 200, 133, 100, and 67 mm focal lengths. As seen from Table 1, all three possible focal lengths of the diffractive lens A, and two out of five focal lengths of the diffractive lens B (400 and 200) can be achromatized. Using Table 1, we identify the focal lengths of the fluidic lens for every focal length of the diffractive lens. Results of the two combined focal lengths develops a predicted achromatic focal length at green wavelength through Фexpected = Фdiffractive + Фfluidic and fexpected = 1/ Фexpected. The five expected achromatic focal lengths, fexpected, for green must be achieved through the experimental setup for the achromat to work properly.

The fluidic lens illustrates a nonlinear response as fluid is withdrawn. As the membrane reaches higher radii, the membrane becomes flatter. The sensitivity to the amount of fluid increases within this range since a smaller amount of fluid varies the curvature. The measured values of the fluidic lenses focal length for the three wavelengths are depicted in Fig. 4 in terms of the amount of fluid injected in the lens.

The final step in producing the variable focal length achromat is the combination of the liquid crystal diffractive lens with the pressure controlled methanol fluidic lens. After adjusting the focal lengths of each lens to the appropriate values dictated by the achromat equation we measured the overall focal length of the hybrid lens at the red, green, and blue wavelengths. The experiment verified that the focus spots of the red and blue wavelengths coincided very closely. Figure 5(a)
Fig. 5 (a-e) Focal spots when the diffractive and fluidic lenses are combined to produce the best focus for the red and the blue lights. The focal length values at the green wavelength are: (a) fdiffractive = 1000 mm, ffluidic = 252 mm; (b) fdiffractive = 500 mm, ffluidic = 126 mm; (c) fdiffractive = 250 mm, ffluidic = 63 mm; (d) fdiffractive = 400 mm, ffluidic = 101 mm; (e) fdiffractive = 200 mm, ffluidic = 51 mm; (f) overall focal length of the hybrid system for the green, red and blue wavelengths.
5(e) depict the focal spots for the red and the blue wavelengths as the focal lengths of the diffractive and the fluidic lenses are varied according to the achromat equation. In Fig. 5(a)5(c) diffractive lens A, and in Fig. 5(d) and 5(e) diffractive lens B was combined with the fluidic lens. The other three focal lengths from the diffractive lens B could not be used for this experiment because of the limited minimum achievable focal length of the fluidic lens in its current form. As the focal length is decreased, the spot size and aberrations are reduced as expected; however, the background scattered light is slightly increased. This is caused by the reduction in diffraction efficiency at the shorter focal lengths as the number of binary phase levels decreases due to the electrode shunting [2

2. P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]

,3

3. P. Valley, M. Reza Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Nonmechanical bifocal zoom telescope,” Opt. Lett. 35(15), 2582–2584 (2010). [CrossRef] [PubMed]

]. The issue of low diffraction efficiency can be overcome by designing diffractive lenses with higher number of binary phase levels which results in smaller electrode sizes if the design optical power and aperture size are kept constant. This will require a more advanced micro-fabrication technique. On the other hand, the fluidic lens showed nearly round and sharp focus spots at short focal lengths when the curvature of the membrane was high, but at long focal lengths as the membrane became flatter considerable aberrations started to show up, of which astigmatism and coma were more pronounced as evident from Fig. 5(a) and 5(b).

Figure 5(f) shows the values of the overall focal length of the hybrid diffractive/fluidic lens for the green, blue and red test wavelengths. As expected, the green light comes to focus first and then the red and blue lights will come into focus near the same plane. The measured focal lengths of the hybrid lens closely matched with the expected focal length values seen from Fig. 5(f). Although our hybrid diffractive/refractive lens has the advantage of being multi-focal and non-mechanical compared to the traditional lenses, its current optical qualities are slightly inferior to the conventional lenses because of the few available focal lengths of our liquid crystal diffractive lenses in their current form and low diffraction efficiencies at shorter focal lengths, as well as physical limitations of our fluidic lens in its current form including small fluid pump, limited aperture size, and significant aberrations at longer focal lengths when the membrane’s curvature is decreased. The chromatic aberration was significantly reduced but not completely at this time corrected due to the current limitations which can be overcome by improving the fabrication.

The clear aperture of our liquid crystal diffractive lenses is limited by the photo-lithography capabilities, number of binary phase levels, and diffraction efficiency, whereas the fluidic lens is aperture limited by the pressure control of the mechanical flanges on the periphery. If the aperture becomes too large then we cannot produce an even distribution of pressure holding down the membrane, inducing uncontrollable aberrations. The function radius of curvature of the fluidic lens is limited by the tensile strength of the designed membrane. Using a broad-band positive photoresist (S1805) and Karl-Suss MA6 contact printer operating around i-line (365 nm), we were able to achieve one micron feature sizes. Employing more advanced fabrication tools smaller features can be made and the design aperture can be increased. This is due to the facts that the Fresnel zones get narrower as moving away from center and as the number of binary phase levels or the design optical power is increased. Diffraction efficiency can also become a limiting factor if the zone widths become comparable to the liquid crystal thickness or the inter-electrode gaps (in case of one-layer electrode design) [2

2. P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]

,3

3. P. Valley, M. Reza Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Nonmechanical bifocal zoom telescope,” Opt. Lett. 35(15), 2582–2584 (2010). [CrossRef] [PubMed]

,17

17. B. Apter, U. Efron, and E. Bahat-Treidel, “On the fringing-field effect in liquid-crystal beam-steering devices,” Appl. Opt. 43(1), 11–19 (2004). [CrossRef] [PubMed]

].

Diffractive lens A has a maximum design aperture of 10 mm, 8 phase levels, 1 diopter minimum optical power, no inter-electrode gaps (odd and even electrodes interleaved into two layers), about 8-micron narrowest electrode, and about 7-micron thick liquid crystal. Diffractive lens B has a maximum design aperture of 6 mm, 12 phase levels, and 2.5 diopter minimum optical power with one micron inter-electrode gaps (one-layer electrode design), about 5-micron narrowest electrode, and about 4-micron thick liquid crystal. To increase the diffraction efficiency, liquid crystal thickness can further be decreased by using smaller glass fiber spacer beads during assembly. However, the minimum thickness in order to achieve at least 2π phase retardation using the E7 liquid crystal and any wavelength shorter than 633 nm would be (λ ΔΦmax) / (2π Δnmax) = λ / Δnmax = 0.633 / 0.225 = 2.8 micron.

In conclusion, we have demonstrated a variable focal length achromatic lens that consists of a variable liquid crystal diffractive lens and a variable pressure-controlled fluidic lens. We used two diffractive lenses that produce multiple discrete focal lengths with an Abbe number of −3.45. The fluidic lens can provide a more continuous variation, and its focal lengths are chosen such that they minimize the dispersion of the diffractive lens. We chose Methanol for the fluidic lens due to its high dispersion properties. Then we combined the fluidic lens and one diffractive lens at a time to minimize the dispersion between the red and blue wavelengths. The lenses showed acceptable optical properties and the test results were close to the theoretical predictions. This adjustable hybrid lens has no moving parts and would be useful for compact color imaging applications, and medical and ophthalmic imaging devices.

Acknowledgments

The authors acknowledge support from the NSF through CIAN ERC grant #EEC-0812072 and NIH grant #R21EY018934.

References and links

1.

D. C. O'Shea, T. J. Suleski, A. D. Kathman, and D. W. Prather, Diffractive Optics: Design, Fabrication, and Test (SPIE Press Book, 2004).

2.

P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]

3.

P. Valley, M. Reza Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Nonmechanical bifocal zoom telescope,” Opt. Lett. 35(15), 2582–2584 (2010). [CrossRef] [PubMed]

4.

S. Sato, A. Sugiyama, and R. Sato, “Variable-focus liquid-crystal fresnel lens,” Jpn. J. Appl. Phys. 24(Part 2, No. 8), L626–L628 (1985). [CrossRef]

5.

H. Ren, Y. H. Fan, and S. T. Wu, “Tunable Fresnel lens using nanoscale polymer-dispersed liquid crystals,” Appl. Phys. Lett. 83(8), 1515–1517 (2003). [CrossRef]

6.

B. E. Bagwell, D. V. Wick, R. Batchko, J. D. Mansell, T. Martinez, S. R. Restaino, D. M. Payne, J. Harriman, S. Serati, G. Sharp, and J. Schwiegerling, “Liquid crystal based active optics,” Proc. SPIE 6289, 628908, 628908-12 (2006). [CrossRef]

7.

H. C. Lin and Y. H. Lin, “An electrically tunable focusing liquid crystal lens with a built-in planar polymeric lens,” Appl. Phys. Lett. 98(8), 083503 (2011). [CrossRef]

8.

O. Pishnyak, S. Sato, and O. D. Lavrentovich, “Electrically tunable lens based on a dual-frequency nematic liquid crystal,” Appl. Opt. 45(19), 4576–4582 (2006). [CrossRef] [PubMed]

9.

H. Ren, Y. H. Fan, S. Gauza, and S. T. Wu, “Tunable-focus flat liquid crystal spherical lens,” Appl. Phys. Lett. 84(23), 4789–4791 (2004). [CrossRef]

10.

D. Y. Zhang, N. Justis, and Y. H. Lo, “Integrated fluidic adaptive zoom lens,” Opt. Lett. 29(24), 2855–2857 (2004). [CrossRef]

11.

H. Ren, D. Fox, P. A. Anderson, B. Wu, and S. T. Wu, “Tunable-focus liquid lens controlled using a servo motor,” Opt. Express 14(18), 8031–8036 (2006). [CrossRef] [PubMed]

12.

R. Marks, D. L. Mathine, G. Peyman, J. Schwiegerling, and N. Peyghambarian, “Adjustable fluidic lenses for ophthalmic corrections,” Opt. Lett. 34(4), 515–517 (2009). [CrossRef] [PubMed]

13.

T. Stone and N. George, “Hybrid diffractive-refractive lenses and achromats,” Appl. Opt. 27(14), 2960–2971 (1988). [CrossRef] [PubMed]

14.

G. Zhou, H. M. Leung, H. Yu, A. S. Kumar, and F. S. Chau, “Liquid tunable diffractive/refractive hybrid lens,” Opt. Lett. 34(18), 2793–2795 (2009). [CrossRef] [PubMed]

15.

J. E. Greivenkamp, Field guide to geometrical optics (SPIE Press, 2004).

16.

M. Daimon and A. Masumura, “Measurement of the refractive index of distilled water from the near-infrared region to the ultraviolet region,” Appl. Opt. 46(18), 3811–3820 (2007). [CrossRef] [PubMed]

17.

B. Apter, U. Efron, and E. Bahat-Treidel, “On the fringing-field effect in liquid-crystal beam-steering devices,” Appl. Opt. 43(1), 11–19 (2004). [CrossRef] [PubMed]

OCIS Codes
(080.3630) Geometric optics : Lenses
(230.3720) Optical devices : Liquid-crystal devices
(050.1965) Diffraction and gratings : Diffractive lenses

ToC Category:
Optical Devices

History
Original Manuscript: January 7, 2011
Revised Manuscript: March 4, 2011
Manuscript Accepted: March 18, 2011
Published: April 4, 2011

Virtual Issues
Vol. 6, Iss. 5 Virtual Journal for Biomedical Optics

Citation
Pouria Valley, Nickolaos Savidis, Jim Schwiegerling, Mohammad Reza Dodge, Gholam Peyman, and N. Peyghambarian, "Adjustable hybrid diffractive/refractive achromatic lens," Opt. Express 19, 7468-7479 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-8-7468


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. D. C. O'Shea, T. J. Suleski, A. D. Kathman, and D. W. Prather, Diffractive Optics: Design, Fabrication, and Test (SPIE Press Book, 2004).
  2. P. Valley, D. L. Mathine, M. R. Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Tunable-focus flat liquid-crystal diffractive lens,” Opt. Lett. 35(3), 336–338 (2010). [CrossRef] [PubMed]
  3. P. Valley, M. Reza Dodge, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Nonmechanical bifocal zoom telescope,” Opt. Lett. 35(15), 2582–2584 (2010). [CrossRef] [PubMed]
  4. S. Sato, A. Sugiyama, and R. Sato, “Variable-focus liquid-crystal fresnel lens,” Jpn. J. Appl. Phys. 24(Part 2, No. 8), L626–L628 (1985). [CrossRef]
  5. H. Ren, Y. H. Fan, and S. T. Wu, “Tunable Fresnel lens using nanoscale polymer-dispersed liquid crystals,” Appl. Phys. Lett. 83(8), 1515–1517 (2003). [CrossRef]
  6. B. E. Bagwell, D. V. Wick, R. Batchko, J. D. Mansell, T. Martinez, S. R. Restaino, D. M. Payne, J. Harriman, S. Serati, G. Sharp, and J. Schwiegerling, “Liquid crystal based active optics,” Proc. SPIE 6289, 628908, 628908-12 (2006). [CrossRef]
  7. H. C. Lin and Y. H. Lin, “An electrically tunable focusing liquid crystal lens with a built-in planar polymeric lens,” Appl. Phys. Lett. 98(8), 083503 (2011). [CrossRef]
  8. O. Pishnyak, S. Sato, and O. D. Lavrentovich, “Electrically tunable lens based on a dual-frequency nematic liquid crystal,” Appl. Opt. 45(19), 4576–4582 (2006). [CrossRef] [PubMed]
  9. H. Ren, Y. H. Fan, S. Gauza, and S. T. Wu, “Tunable-focus flat liquid crystal spherical lens,” Appl. Phys. Lett. 84(23), 4789–4791 (2004). [CrossRef]
  10. D. Y. Zhang, N. Justis, and Y. H. Lo, “Integrated fluidic adaptive zoom lens,” Opt. Lett. 29(24), 2855–2857 (2004). [CrossRef]
  11. H. Ren, D. Fox, P. A. Anderson, B. Wu, and S. T. Wu, “Tunable-focus liquid lens controlled using a servo motor,” Opt. Express 14(18), 8031–8036 (2006). [CrossRef] [PubMed]
  12. R. Marks, D. L. Mathine, G. Peyman, J. Schwiegerling, and N. Peyghambarian, “Adjustable fluidic lenses for ophthalmic corrections,” Opt. Lett. 34(4), 515–517 (2009). [CrossRef] [PubMed]
  13. T. Stone and N. George, “Hybrid diffractive-refractive lenses and achromats,” Appl. Opt. 27(14), 2960–2971 (1988). [CrossRef] [PubMed]
  14. G. Zhou, H. M. Leung, H. Yu, A. S. Kumar, and F. S. Chau, “Liquid tunable diffractive/refractive hybrid lens,” Opt. Lett. 34(18), 2793–2795 (2009). [CrossRef] [PubMed]
  15. J. E. Greivenkamp, Field guide to geometrical optics (SPIE Press, 2004).
  16. M. Daimon and A. Masumura, “Measurement of the refractive index of distilled water from the near-infrared region to the ultraviolet region,” Appl. Opt. 46(18), 3811–3820 (2007). [CrossRef] [PubMed]
  17. B. Apter, U. Efron, and E. Bahat-Treidel, “On the fringing-field effect in liquid-crystal beam-steering devices,” Appl. Opt. 43(1), 11–19 (2004). [CrossRef] [PubMed]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1 Fig. 4 Fig. 2
 
Fig. 3 Fig. 5
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited