In this article, a novel optical metrology and calibration device is designed, which can be used for the metrology and calibration of ophthalmic optical instrument - fundus cameras. Fundus camera is widely used in the field of diagnosing fundus diseases due to its high accuracy, simple structure and easy operation. The model eye we designed, including the cornea, lens and other major refractive parts of human eye can test multiple key parameters of fundus cameras, such as resolution, field of view, diopter and so on. A resolution board with micron-level precision for the detection of resolution is designed and processed by coating technology. The mechanical structures of the model eye including the cyclic structure for testing the field of view are designed and processed by 3D printing technology. In addition, different diopters have been developed for simulating nearsightedness and farsightedness. Testing results show that the model eye we designed can be used for metrology and calibration of fundus cameras, and has the advantages of high accuracy, high integration, strong stability and applicability.
The traditional single reference arm swept-source optical coherence tomography (SSOCT) has the ability to image 7mm axial length, however larger depth can not be obtained directly. Conventionally, the extending depth can be obtained via special system design or multi-arm imaging. However, in this paper we design a SSOCT system with large detection depth which only need one reference arm. The difference between this system and the traditional is that the proposed system use a high-speed scanning laser. The large imaging depth range is achieved owing to the increased k-trigger number and the related sample point number in one A-scan period. The sample signal and the reference signal interfere in the optical fiber coupler, and then it is detected by a balanced detector. The digital signal of each A-line goes through spectrum shaping, background removal, mirror image removal, dispersion matching and the Fourier transform, then the A-scan signal can be obtained. 512 A-scan signal comprise the B-scan frame. The imaging depth can reach 54mm, and the axial imaging resolution is 7.5 μm . The frame rate is 5fps of the SSOCT system which can be improved if algorithm is simplified further. The system can be employed in human eye axial-length measurement and dimensional measurement.
Two-step phase-shifting sectioning structured light illumination microscopy (TSSIM) that reconstructs a three-dimensional structure using Fourier transform is proposed. Undesirable background signals corresponding to out-of-focus signals are eliminated using this method. Since there is no restriction for accurate phase shifts, this method does not suffer from large retrieval errors, unlike conventional sectioning structured illumination wide-field fluorescence microscopy (SSIWM). It can be used directly without modifying the conventional SSIWM microscope setup employing two of the three captured images, and can be applied to both shape measurements and biological observation. Less exposure time is required; thus, photobleaching and phototoxicity in biological observation are reduced. Further, the impact of the phase-shift difference on the signal-to-noise ratio of reconstruction image is analyzed. Both simulations and experiments are presented to show the validity of the proposed method.
We propose fast, economical one-shot optical sectioning structured illumination microscopy (OSSIM) based on the sectioning structured illumination wide-field fluorescence microscopy (SSIWM). Unlike using three precise known phase patterns in conventional three-step SSIWM, every section of the specimen is modulated using a one-dimensional sinusoidal pattern with an arbitrary phase in the proposed method. There are few steps to get the section image from the modulated image. A fringe-free spectrum is obtained using a filter in the Fourier domain, and the reconstructed section is recovered from its inverse Fourier transform and the modulus calculation. In the conventional SSIWM, the accurate positioning is demanded to match the three phases perfectly to avoid artificial fringe on the reconstructed image. Compared with three-step SSIWM, OSSIM shows reduced illumination and observation time, specimen damage, and it avoids reconstruction artefacts resulting from inaccurate phase-shift. Furthermore, OSSIM can directly utilize images captured using SSIWM without modifying the setup. The proposed method is supported by a series of derivations and is validated through simulations and experiments.
Optical coherence tomography (OCT) and confocal scanning microscopes can perform three dimensional (3D) optical imaging of target objects. They are widely used in many fields because of their non-contact measurement, real-time fast imaging and high resolution. This paper is dedicated to evaluating the resolution of 3D optical imaging systems, enabling third-party metrology assessment, assuring periodic quality, and comparing different systems. An improved standard test method based on the system 3D point spread function (PSF) is proposed in this paper. The standard diameter microspheres were embedded in the robust PSF phantoms as scattering particles. An OCT and a confocal scanning microscope were used to acquire the 3D PSF images. Different from previous studies, this paper proposes a new preparation process for PSF phantoms. In addition, new mathematical model was built based on statistical methods to analyze the PSF that includes hundreds of scattered data. Combining the imaging principles of OCT and confocal microscopy, the imaging resolution of the two optical systems was compared. Finally, a stability experiment was performed to further verify the feasibility of using the PSF to evaluate the resolution performance of the imaging system. The results showed that the resolution based on PSF analysis is in good agreement with the theoretically calculated value, and this method can be used to reliably evaluate the resolution of 3D optical imaging system in the future.
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