Open Access
Add to BibSonomyAbstract
Substantial aberrations are ubiquitous in many conventional adaptive lenses due to the existence of deformable interface and thus inevitably compromise the optical performance. In this paper, we introduce a novel concept of dual-function fluidic lenses (DFFL) with a built-in aspheric polydimethylsiloxane lens (APL) to enable the design of a compact optical system with tunable imaging and aberration suppression properties. This is achieved by varying both hydrostatic pressures (i.e. adjusting the injected liquid volume change) such that a widely tunable focal length and the simultaneously integrated APL for aberrations correction. DFFL can transform to 4 modes: microscopic mode (APL only), APL/concave mode, APL/plano mode, and APL/convex mode. Focal tunability of DFFL from 12/8 mm to about 90/65 mm (DI water/ethanol) is demonstrated without any mechanical moving components. Aberration characterization is carried out systematically and the low cost, high performance microscopic mode can be easily achieved by actuating the contact between APL and PDMS membrane. In addition, DFFL turning to microscopic mode (focal length 7.32 mm and magnification 50X) can rival the images quality of commercial microscopes.
© 2015 Optical Society of America
1. Introduction
Adaptive and focus tunable lenses facilitate the facile design of cost-efficient and highly flexible compact optical systems without the need of any mechanical moving parts or actual physical displacement of the lenses. Two major categories exist in traditional focus tunable lenses include changing in either refractive index of the optical medium or the lens curvature [1].However, probably the most compact and efficient adaptive lenses are human eye with the aid of ciliary muscles [2]. Previously, different types of adaptive lens and associated properties such as dynamical tunability had been proposed [3]. For example, an appropriately reconfigured liquids interface radii combined with suitable optical liquids can be used to make a lens with diffraction-limited resolution over a wide focal tuning range [4]. Various actuation mechanisms can be used to induce the shape changes like stimuli-responsive hydrogels [5], photo-polymer [6] and electromagnetic actuators [7]. In terms of other functionality, deformable liquid droplets can be used for miniature cameras with optical zoom [8], optical beam control [9] and optical switch with a reconfigurable dielectric liquid droplet [10]. On the other hand, aspheric lenses offer the advantage of compact optics with a small number of elements yet maintain excellent aberration correction performance [11]. Aspheric elements are currently used for correcting distortion in wide-angle lenses [12], longitudinal spherical aberration (LSA) correction [13], contact lenses design [14] and intraocular lens (IOL) [15, 16]. Furthermore, by integrating the aspheric lenses with conventional adaptive lenses, substantial spherical aberration can be minimized [17]. One of the fabrication methods for a typical aspheric PDMS lens (APL) is using the hanging droplet technique. Gravity driven equilibrium between the interfacial energies of liquid, air and solid surfaces [18, 19], the fabricated droplet can be used to magnify small structures [18, 20] and heralds a new paradigm in the mass-manufacture processes [21]. Other method for the aberration correction includes the concept of adaptive optics (AO). In astronomy field, the atmospheric turbulence that confines the performance of ground-based telescope is shown to be compensated [22, 23]. In addition, the improved in vivo imaging of the retina for ocular aberration and ophthalmic applications [24, 25], an integrated roughness measurement system based on AO and binary analysis of speckle pattern images [26] and laser-scattering phenomena [27] are demonstrated. In addition, an oscillation-free implementation of an optical beam control device with reconfigurable fluidic lens is demonstrated [28], considering the AO enhancement [29]. In microscopy, AO has also been applied to multiphoton microscopy and images of several layers mismatched and inhomogeneous refractive index [30], high numerical aperture (NA) objectives [31], refractive- index-mismatch (RIM) [32, 33] and microlenses with flexible elastomers [34].
In this paper, a novel concept of dual-function fluidic lens with superior imaging performance, called dual-function fluidic lens (DFFL), which is composed of tunable fluidic lens and APL, working individually/collectively to achieve dual-functions of microscopic or tunable lens operation. The paper will be structured in the following sections. In sections 2, we describe the process of DFFL fabrication. First, fabricate APL with method of hanging droplets which allow DFFL to microscopic mode and has magnification 50x. It is straightforward to reduce the aberrations of fluidic lens with integrated APL in the present experiments. Next, 4 modes of operations are demonstrated as microscopic mode (APL only), APL/concave mode, APL/plano mode, and APL/convex mode. In sections 3, we measure optical properties of DFFL: measuring the focal length without/with APL and aberrations-reduction effect by adding APL, comparing the aberrations of microscopic mode (APL only) against a commercial microscope, and demonstrating tunable imaging properties of DFFL with each 4 mode. We anticipate that our approach will pave the way for a new generation of adaptive optofluidic devices with superior optical performance.
Fabricate dual function fluidic lenses (DFFL)
Aspheric polydimethylsiloxane (PDMS, n = 1.4) lens (APL) is a crucial component with shorter focal lengths and higher magnification [21]. The fabrication of APL is utilized by sequentially depositing, inverting and curing smaller volume droplets onto previously cured PDMS droplets. The flow chart in Fig. 1(a) to (d) list key fabrication steps as dropping and depositing PDMS solutions into wells, inverting the wells, heating up and curing PDMS solutions in ovens. The initial mixing process follows the typical soft lithography PDMS recipe (2 parts - Sylgard 184, Dow Corning), which is to mix the PDMS base with the curing agent by weight ratio 10:1. In Fig. 1(b), after mixing the PDMS solutions and removing residue bubbles by placed in a vacuum, a syringe (Terumo) is dipped vertically into the mixture to extract a small drop about 10 ml. In Fig. 1(c) the drop is deposited on top of the inverted polystyrene wells and cured in an oven at 70°C for 1 hour. Fabricated APL as shown in Fig. 1(d) has a dimension of 2.8 mm height and 7.32 mm diameter.
Fig. 1 Schematics of APL fabrication process illustrated as (a) controllably dipping PDMS solutions into the receiving wells, (b) gravity induced action by inverting the wells, (c) thermally curing and stabilizing by heating in an oven for 70。C and 1 hour. (d) APL fabrication complete and retrieve. (e) Schematic for the construction of DFFL with an explosive view, showing the deformable PDMS membrane, acrylic chamber, optical glass and APL. The assembly components of view for the DFFL are shown in (f). Constructed prototype of DFFL and optical photo are shown in (g). (I) - (IV), the tunable shapes of the DFFL vary with injected volume in microscopic mode (I, APL only), APL/concave mode (II), APL/plano mode (III), and APL/convex mode (IV), respectively. Scale bar: 5mm.
Detail construction of DFFL is shown in an explosive and assembly views in Fig. 1(e) and Fig. 1(f), respectively. An indispensable component of the DFFL is a PDMS elastomeric membrane that can be deformed to change the focal length. The fabrication process of PDMS membrane is similar to aforementioned APL and with thickness to be approximately 550 μm. The fluidic chamber serves as a stiff frame and made by acrylic (1 mm thick) which height and diameter are 3.5 mm and diameter 10 mm, respectively. A syringe connected tapped hole is designed to provide volumetric changes. The bottom portion of the DFFL is consists of square glass (1 mm thick, Menzel-Glaser, Superfost, refractive index 1.523). The optical photo of fabricated DFFL as shown in Fig. 1(g) is constructed from a stiff frame, a transparent liquid of fixed volume, elastomeric membranes and APL. DFFL achieved a wide range of focal length tunability and in general can be varied in a combination of APL dimension, the refractive index of the liquid and the extent of the membrane bulging. The focal length of the DFFL can be designed to increase or decrease depending on injected volume, i.e., as the positively or negatively actuated radius of curvature membrane, respectively.
2. Optical qualities
Initially, the integration of APL is not performed and the fluidic lenses for DI water/ethanol with different focal lengths as well as different lens types such as plano/convex and plano/concave, the measured focal lengths for both convex and concave lens types as a function of the injected volume are firstly presented in Fig. 2(a). It is noted that the absolute values of the focal length of both types of fluidic lenses for DI water/ethanol cover a wide range – from 20/16 to about 90/80 mm. Secondary for the inclusion of APL, when light passes APL without any medium of fluid, light has been suddenly converged and the focal length is experimentally measured as 7.32 mm with the magnification 50X. Third, we add the adaptive fluid lens with a deformable membrane, which 3 types of cooperatively functioned lenses with various shapes and focal length can be directly changed by adjusting volume of fluid lens.
Fig. 2 (a)Measured focal length as a function of the injected/withdraw volume for both types and liquids of fluidic lens without APL. (b) Measured focal length for 4 modes –in microscopic mode (I, APL only), APL/concave mode (II), APL/plano mode (III), and APL/convex mode (IV), respectively, as a function of the injected/withdraw volume for 2 refractive index liquids, and the resultant configurations of PDMS membrane is shown in (c). The focal length of DFFL contained wide range in the microscopic mode at 7.32 mm (magnification 50X) and 12.96/8.7mm to 91.4/63.9 mm for the DI water /ethanol, respectively.
Figure 2(b) depicts the change in DFFL focal length with injected/withdraw volume and several geometrical configurations can be sequentially tuned to achieve various focal length range. The measurement results demonstrate the capability of the DFFL with different focal lengths as a result of four operational schemes in microscopic mode (I, APL only), APL/concave mode (II), APL/plano mode (III), and APL/convex mode (IV), respectively. For the microscopic mode of APL only (I), the proposed device is basically the low cost portable microscope since the PDMS membrane touched the APL without any medium of liquids between each other, DFFL immediately turns to the microscopic mode which the focal length rapidly decreases to 7.32 mm and the magnification approximately raises to 50X. Similarly, the focal length of the DFFL is adjustable by simply regulating the fluidic volume. By continually increasing/decreasing the volume of fluid in the reservoir to stretch/compress the membrane in the configurations of convex/concave respectively, a variable focal length can be varied continuously. For the APL/concave mode (II), APL/plano mode (III), and APL/convex mode (IV), the measured focal length change for DI water /ethanol are measured to be 30/20 to about 90/70 mm (withdraw volume −0.01 to −0.07 ml, APL/concave mode), 27.99/20.5 mm(injected volume 0 ml, APL/plano mode) and 25/14 to about 12/8 mm (injected volume 0.01 to 0.2 ml, APL/convex mode), respectively. It is noted that the remarkable functions and values of the focal length of microscopic mode (I, APL only), APL/concave mode (II), APL/plano mode (III), and APL/convex mode (IV) of DFFL covers an astoundingly wide range of 7.32mm and 12/8 to about 90/70 mm for the DI water /ethanol respectively. Optical property of the effect of liquid refractive index is also experimentally investigated using DI water /ethanol respectively. The slightly higher tunable range of focus in using DI water as compared with ethanol is mainly due to the refractive index difference. The refractive index of DI water is lower than ethanol. Lower refractive index will diverge light so that DFFL has higher tunable range with DI water.
Figure 2(c) shows the schematics of between the injected various fluid volumes and the resultant PDMS membrane variations as shown in mode (I) to (IV). The red, green, purple and black curves represent the 4 types of the membrane shapes as well as corresponding image planes. It is concluded that the focus can be consistently tuned and agrees well with the theoretical analysis for the membrane deformations under uniform pressure. Furthermore, the novel design to incorporate APL into liquid tunable lens will further justified by the detail aberration analysis presented in next session.
Also, the injected volume can be analytically correlated to the lens curvature as the lens sag (h) is calculated as [35]:
Where rc is the curvature of deformed PDMS membrane by injected volume and d is diameter of DEEL.Figure 3. shows the relationships which the injected volume of 0.2 ml (APL/convex mode), 0 ml (APL/plano mode), and withdraw 0.07 ml (microscopic mode)DI water/ethanol can produce lens curvatures of 5.15 mm, ∞ mm and −4.94 mm, respectively.
Fig. 3 Schematic of 3 curvatures for DFFL. Injected volumes of 0.2 ml (APL/convex mode), 0 ml (APL/plano mode), and withdraw 0.07 ml (microscopic mode) DI water/ethanol can be measured to produce lens curvatures of 5.86 mm, ∞ mm and 5.1 mm, respectively.
We compare DFFL for microscopic mode with the commercial microscope objective lens (50 × 0.75NA, Nikon, LE Plan) via the measurement of wavefront aberrations by Shack–Hartmann wavefront sensor (S–H) (Thorlabs, Inc. λ = 400 nm-1100 nm). In Fig. 4(a), it can be clearly seen that the overall wavefront aberrations of the DFFL for microscopic mode are comparable to those of the commercially available microscope objective lens. It's obvious that almost the first 5 Zernike polynomials are extremely close. The measured wavefront maps for corresponding RMS aberrations by DFFL and microscope objective lens are presented in Fig. 4(b), (c) respectively. It's evident that results of RMS errors for wavefront maps are quite similar and the maximum RMS values difference for both DFFL and microscope objective lens are less than 5.8%. Only a marginally higher Y-tilt (Z3) term is present for the proposed APL microscopic mode than commercial microscope objective lens as measured to 1.053/0.72 μm, respectively. The main reason may be attributed to the slightly tilted surface during curing process when putting the inverse PDMS droplets as shown in Fig. 1(c). This small inaccuracy in Y-tilt (Z3) term can be overcome by using a high stiffness curing table and pre-calibrated to the precision of 2 um. To summarize, DFFL for microscopic mode can be a low cost and high performance option and extended function for future smart lenses.
Fig. 4 Comparison of wavefront aberrations for the APL and generally commercial object lens for first 5 Zernike modes. (b), (c) are wavefront maps for APL and the commercial object lens, respectively. APL can rival commercial microscope objective lens by comparing both wavefront aberrations and wavefront maps.
To compare the image quality for liquid of different refractive index and effect of APL improvement, wavefront aberrations are systematically measured. It's apparent that for both DI water and ethanol without APL, the aberrations represented by Zernike coefficients of piston (Z1) and defocus (Z4) terms will incrementally increase as the increase of injection volume as shown in Fig. 5(a). The other terms have relatively little impact by the increase of injection volume. Next, we install APL into fluidic chambers and measure the wavefront aberrations. Obviously, Z1, Z4 and Z5 terms have reduced significantly for both DI water and ethanol after adding APL in Fig. 5(b). For example, the Z1 aberration for DI water without/with APL integration is measured as 1.658/0.945 μm, respectively for the APL/concave mode (injected volume −0.07 ml, focal length 91.4 mm). Similar aberration improvement can be measured by using the ethanol and other operational modes of proposed device at various focal range. For example, the Z4 for ethanol without/with APL is measured as 0.337/0.0084 μm respectively for APL/plano mode (injected volume 0 ml, focal length 20.5 mm), showing a remarkable aberration correction capability. The detail data for measured Zernike coefficients (Z1 - Z5) without/with APL as a function of injected volume for DI water/ethanol are shown in Table 1.-Furthermore, both X-Tilt (Z2)term and Y-Tilt (Z3) terms have the same tendency to reduce aberrations.-For instance, similar trend can be found on the X-Tilt (Z2) aberration for the focal 20.92 mm in APL/convex mode, the APL-integrated device for DI water can reduce aberration from 0.247 to 0.173 μm (injected volume 0.03 ml). And for Y-Tilt (Z3) term, the aberration for the focal length 55.5 mm (APL/concave mode), the APL-integrated device can reduce aberration from −0.546 to −0.19 μm (injected volume −0.05 ml).-Meanwhile, focal length 12.54 mm (APL/convex mode) has reduced from −0.414 to −0.222 (injected volume 0.05 ml).
Fig. 5 Zernike coefficients of first 5 terms are extracted from the Shack–Hartmann measurements for 2 refractive index liquids. Comparison of Injected DI water (a) and ethanol (b) without and with APL. After adding APL, the Zernike coefficients of Z1 and Z4 terms have been improved to promote the sharpness and contrast of the images.
Table 1. Measured Zernike coefficients (Z1 - Z5) without/with APL by injected volume of DI water/ethanol.
Next, we take 4 samples to show the APL capability of aberration-reduction in Fig. 5, at the same focal length . Since the additon of APL will inevitably change the focal length accordingly, therefore, different injected volume should be applied to the DFFL without/with APL integration, in order to achieve the same focal length. DFFL#1 has a fixed focal length f = 20 mm and injected DI water without/with APL is 0.03/0.07 ml, respectively. The APL correction results as shown in Fig. 6(a) show that the Z1 - Z5 terms can be effectively minimized. In particular, the Z1 term shows a dramatical decrease by 70%, from 1.615 to 0.482um. We compare the performance without/with APL as shown in Fig. 6(b). It is noted that a characteristic pincushion distortion prevails in images of 1951 USAF target card as induced by the deformed membrane of spherical shape as test structures taken without APL. In comparison, image taken with APL is more sharpness with a improved significantly pincushion distortion. Thus, APL can reduce aberration effectively and enhance the image quality. Simarly, DFFL #2 of focal length f = 33 mm also indicated the trend of the image improvement for the proposed DFFL in Fig. 6(c). For the case of ethanol as the injected liquid has the same trend for aberration reduction. For instance, in Fig. 5(d) Z1 terms of DFFL #3 with f = 30 mm has decreased from 1.358 to 0.311 um. Also, DFFL #4 with f = 55 mm has similar tendency to previous samples . Overall, the APL correction results demonstrated that the Z1 - Z5 terms can be effectively minimized as compared to the original tunable liquid lenses configuration.
Fig. 6 Comparison of wavefront aberrations as a function of the injected volume [DI water for (a), (c) and ethanol for (d), (e)] for the DFFL without/with APL at the same focal length. (a)DFFL #1 for injected DI water without/with APL for f = 20 mm (injected volume 0.03/0.07 ml). (b)Induced aberrations (pincushion distortion) of fluidic lens without APL (left) and with APL-correction (right) demonstrate the suppression of aberrations based on the image taken of a 1951 USAF target card. (c)DFFL #2 Injected DI water without/with APL for f = 33 mm (injected volume 0.05/-0.01 ml). (d)DFFL #3 Injected ethanol without/with APL for f = 30 mm (injected volume 0.04/-0.03 ml). (e)DFFL #4 Injected ethanol without/with APL for f = 55 mm (injected volume 0.02/-0.05 ml). Scale bar: (b) 1cm.
The APL can effectively correct aberration due to the fact of aspheric shape such that can be accommodated to the stringent requirement of high quality images. In addition, the measured overall Zernike coefficients for ethanol are less than DI water. To sum up, DFFL with ethanol-driven is a better choice to tuning focal length and capture good images.
3. Image performance
The optical performance of the proposed lens is further qualitatively by taking images of objects located at different distances and onto a CCD camera. According to the result of measurement in Fig. 4, the overall Zernike coefficients of ethanol are less than DI water. Therefore, DFFL with ethanol is adopted to take related the images. The experimental setup and captured images are shown in Fig. 7. The testing procedure is initially mounted the DFFL lens at a fixed distance from the CCD sensor and routinely obtained the focal plane by continuously adjusting the fluid volume to receive the sharpest image of each object. It is concluded that the focus can be easily tuned by adjusting the liquid volume. Figure 7(a) shows the photographs for the image quality at different focal lengths of 7.32 mm (microscopic mode, APL only), 14.32 mm (injected volume 0.01 ml, APL/convex mode), 20.5 mm (injected volume 0 ml, APL/plano mode) and 55.5 mm (injected volume −0.05 ml, APL/concave mode), respectively. Above focal length tunability and functional versatility of microscopic mode can be achieved by simply changing the fluid volume in the DFFL. The schematics of deformation states of PDMS membrane during the DFFL focus tuning on the targets of various focal planes are shown in Fig. 7(c). The proposed DFFL lens is versatile with two distinctively different functions and capable of producing relatively good images with low aberration of the objects at various operation modes. The extensive tuning range can be widely used via DFFL and easily transformed any smart phone into the microscopic device as well as optically tunable multi-function lens.
Fig. 7 (a) Photographic images at various focal lengths as captured by a CCD image sensor demonstrating of the focusing capability of the lens. (b) A schematic of the measurement setup used for image acquisition. (c) The deformation states of DFFL at various focal lengths and four operation modes.
4. Conclusion
A simple and compact tunable adaptive lenses have been demonstrated which consists of an elastomer-liquid lens system with a built-in APL located directly in the optical path. Lenses built using this concept yield relatively large focal length changes of more than 640% (14mm-90mm) and improved image quality due to integrated APL for aberration compensation. Furthermore, only a minimal number of components is required: a frame, PDSM membrane, APL, a clear liquid and a simple liquid driven mechanism. Experimentally, adjusting the injected liquid volume (DI water and ethanol) can lead to curvature change and thus reconfigure the focal length accordingly. The fabricated DFFL are allowed to extensive and versatile applications in various 4 modes of operation: microscopic mode (APL only), APL/concave mode, APL/plano mode, and APL/convex mode. For the proposed structure of DFFL, focal tunability for DI water/ethanol from 12/8 mm to about 90/65 mm is demonstrated without any mechanical moving components. Moreover, when DFFL turn to microscopic mode, which the focal length 7.32 mm and magnification 50X, the image quality can rival commercial microscopes. The optical properties of DFFL are characterized by the Shack–Hartmann measurements. Experimentally by adding APL, suppression of aberrations is demonstrated with significantly enhanced images quality. It's noteworthy that Zernike coefficients, especially Z1 and Z4 terms, can be apparently improved by adding APL which can promote the sharpness and contrast of images.
Reference and links
1. D. Y. Zhang, V. Lien, Y. Berdichevsky, J. Choi, and Y. H. Lo, “Fluidic adaptive lens with high focal length tunability,” Appl. Phys. Lett. 82(19), 3171–3172 (2003). [CrossRef]
2. F. M. Toates, “Accommodation function of the human eye,” Physiol. Rev. 52(4), 828–863 (1972). [PubMed]
3. D.-Y. Zhang, N. Justis, and Y.-H. Lo, “Fluidic adaptive lens of transformable lens type,” Appl. Phys. Lett. 84(21), 4194–4196 (2004). [CrossRef]
4. S. Reichelt and H. Zappe, “Design of spherically corrected, achromatic variable-focus liquid lenses,” Opt. Express 15(21), 14146–14154 (2007). [CrossRef] [PubMed]
5. L. Dong, A. K. Agarwal, D. J. Beebe, and H. Jiang, “Adaptive liquid microlenses activated by stimuli-responsive hydrogels,” Nature 442(7102), 551–554 (2006). [CrossRef] [PubMed]
6. S. Xu, H. Ren, Y. J. Lin, M. G. J. Moharam, S. T. Wu, and N. Tabiryan, “Adaptive liquid lens actuated by photo-polymer,” Opt. Express 17(20), 17590–17595 (2009). [CrossRef] [PubMed]
7. S. W. Lee and S. S. Lee, “Focal tunable liquid lens integrated with an electromagnetic actuator,” Appl. Phys. Lett. 90(12), 121129 (2007). [CrossRef]
8. S. Kuiper and B. H. W. Hendriks, “Variable-focus liquid lens for miniature cameras,” Appl. Phys. Lett. 85(7), 1128–1130 (2004). [CrossRef]
9. H. Ren, S. Xu, and S. T. Wu, “Deformable liquid droplets for optical beam control,” Opt. Express 18(11), 11904–11910 (2010). [CrossRef] [PubMed]
10. H. Ren, S. Xu, D. Ren, and S. T. Wu, “Novel optical switch with a reconfigurable dielectric liquid droplet,” Opt. Express 19(3), 1985–1990 (2011). [CrossRef] [PubMed]
11. D.-K. Lee, Y.-S. Yang, S.-S. Kim, H.-J. Kim, and J.-H. Kim, “Development of a F-Theta Lens for a Laser Scanning Unit,” J. Korean Phys. Soc. 53(5), 2527–2530 (2008).
12. W.-L. Liang, H.-K. Shen, and G.-D. J. Su, “Wide-angle camera with multichannel architecture using microlenses on a curved surface,” Appl. Opt. 53(17), 3696–3705 (2014). [CrossRef] [PubMed]
13. G. Castillo-Santiago, M. Avendaño-Alejo, R. Díaz-Uribe, and L. Castañeda, “Catadioptric null test of ultra-deep concave aspheric lens in wide-field optical system,” Appl. Opt. 53(22), 4939–4946 (2014). [CrossRef] [PubMed]
14. S. Koh, N. Maeda, T. Hamada, and K. Nishida, “Efficacy of spherical aberration correction based on contact lens power,” Cont. Lens Anterior Eye 37(4), 273–277 (2014). [CrossRef] [PubMed]
15. R. Khoramnia, A. Fitting, T. M. Rabsilber, B. C. Thomas, G. U. Auffarth, and M. P. Holzer, “Functional results after implantation of an aspheric, aberration-neutral intraocular lens,” Klin. Monatsbl. Augenheilkd. 232(2), 181–188 (2015). [PubMed]
16. Y. Nochez, S. Majzoub, and P.-J. Pisella, “Effect of interaction of macroaberrations and scattered light on objective quality of vision in pseudophakic eyes with aspheric monofocal intraocular lenses,” J. Cataract Refract. Surg. 38(4), 633–640 (2012). [CrossRef] [PubMed]
17. K. Mishra, C. Murade, B. Carreel, I. Roghair, J. M. Oh, G. Manukyan, D. van den Ende, and F. Mugele, “Optofluidic lens with tunable focal length and asphericity,” Sci. Rep. 4, 6378 (2014). [CrossRef] [PubMed]
18. H. Ren, S. Xu, and S.-T. Wu, “Effects of gravity on the shape of liquid droplets,” Opt. Commun. 283(17), 3255–3258 (2010). [CrossRef]
19. R. Tadmor, P. Bahadur, A. Leh, H. E. N’guessan, R. Jaini, and L. Dang, “Measurement of Lateral Adhesion Forces at the Interface Between a Liquid Drop and a Substrate,” Phys. Rev. Lett. 103(26), 266101 (2009). [CrossRef] [PubMed]
20. F. A. Chowdhury and K. J. Chau, “Variable focus microscopy using a suspended water droplet,” J. Opt. 14(5), 055501 (2012). [CrossRef]
21. W. M. Lee, A. Upadhya, P. J. Reece, and T. G. Phan, “Fabricating low cost and high performance elastomer lenses using hanging droplets,” Biomed. Opt. Express 5(5), 1626–1635 (2014). [CrossRef] [PubMed]
22. C. Rao, L. Zhu, X. Rao, C. Guan, D. Chen, J. Lin, and Z. Liu, “37-Element solar adaptive optics for 26-cm solar fine structure telescope at Yunnan Astronomical Observatory,” Chin. Opt. Lett. 8(10), 966–968 (2010). [CrossRef]
23. J. Aceituno, S. F. Sanchez, J. L. Ortiz, and F. J. Aceituno, “SAOLIM, prototype of a low-cost system for adaptive optics with lucky imaging. Design and performance,” Publ. Astron. Soc. Pac. 122(894), 924–934 (2010). [CrossRef]
24. Y. Zhang, S. Poonja, and A. Roorda, “MEMS-based adaptive optics scanning laser ophthalmoscopy,” Opt. Lett. 31(9), 1268–1270 (2006). [CrossRef] [PubMed]
25. G. Shi, Y. Dai, L. Wang, Z. Ding, X. Rao, and Y. Zhang, “Adaptive optics optical coherence tomography for retina imaging,” Chin. Opt. Lett. 6(6), 424–425 (2008). [CrossRef]
26. Y. K. Fuh, K. C. Hsu, and J. R. Fan, “Rapid in-process measurement of surface roughness using adaptive optics,” Opt. Lett. 37(5), 848–850 (2012). [CrossRef] [PubMed]
27. Y. K. Fuh, K. C. Hsu, and J. R. Fan, “Roughness measurement of metals using a modified binary speckle image and adaptive optics,” Opt. Lasers Eng. 50(3), 312–316 (2012). [CrossRef]
28. Y.-K. Fuh, W.-C. Huang, Y.-S. Lee, and S. Lee, “An oscillation-free actuation of fluidic lens for optical beam control,” Appl. Phys. Lett. 101(7), 071901 (2012). [CrossRef]
29. Y. K. Fuh and W.-C. Huang, “Adaptive optics assisted reconfigurable liquid-driven optical switch,” Opt. Commun. 300(15), 85–89 (2013). [CrossRef]
30. J. W. Cha, J. Ballesta, and P. T. C. So, “Shack-Hartmann wavefront-sensor-based adaptive optics system for multiphoton microscopy,” J. Biomed. Opt. 15(4), 046022 (2010). [CrossRef] [PubMed]
31. L. Sherman, J. Y. Ye, O. Albert, and T. B. Norris, “Adaptive correction of depth-induced aberrations in multiphoton scanning microscopy using a deformable mirror,” J. Microsc. 206(Pt 1), 65–71 (2002). [CrossRef] [PubMed]
32. M. J. Booth and T. Wilson, “Refractive-index-mismatch induced aberrations in single-photon and two-photon microscopy and the use of aberration correction,” J. Biomed. Opt. 6(3), 266–272 (2001). [CrossRef] [PubMed]
33. J. M. Girkin, S. Poland, and A. J. Wright, “Adaptive optics for deeper imaging of biological samples,” Curr. Opin. Biotechnol. 20(1), 106–110 (2009). [CrossRef] [PubMed]
34. P. Liebetraut, S. Petsch, J. Liebeskind, and H. Zappe, “Elastomeric lenses with tunable astigmatism,” Light Sci. Appl. 2, e98 (2013).
35. R. Marks, D. L. Mathine, J. Schwiegerling, G. Peyman, and N. Peyghambarian, “Astigmatism and defocus wavefront correction via Zernike modes produced with fluidic lenses,” Appl. Opt. 48(19), 3580–3587 (2009). [CrossRef] [PubMed]
