Design, assembly, and optical bench testing of a high-numerical-aperture miniature injection-molded objective for fiber-optic confocal reflectance microscopy

Abstract

The design, analysis, assembly methods, and optical-bench test results for a miniature injection-molded plastic objective lens used in a fiber-optic confocal reflectance microscope are presented. The five-lens plastic objective was tested as a stand-alone optical system before its integration into a confocal microscope for in vivo imaging of cells and tissue. Changing the spacing and rotation of the individual optical elements can compensate for fabrication inaccuracies and improve performance. The system performance of the miniature objective lens is measured by use of an industry-accepted slanted-edge modulation transfer function (MTF) metric. An estimated Strehl ratio of 0.61 and a MTF value of 0.66 at the fiber-optic bundle Nyquist frequency have been obtained. The optical bench testing system is configured to permit interactive optical alignment during testing to optimize performance. These results are part of an effort to demonstrate the manufacturability of low-cost, high-performance biomedical optics for high-resolution in vivo imaging. Disposable endoscopic microscope objectives could help in vivo confocal microscopy technology mature to permit wide-scale clinical screening and detection of early cancers and precancerous lesions.

Development of a universal, tunable, miniature fluorescence microscope for use at the point of care

“…The horizontal intensity cross-sections through the smallest resolvable group of the USAF target, visualized in the fifth column, for the five test wavelengths are presented in the right most column of Table 4. The system was also evaluated using the slanted edge technique [14] yielding a Strehl Ratio of 0.73 (the measurement was performed on-axis for a wavelength of 700 nm).…”

High-resolution resonant and nonresonant fiber-scanning confocal microscope

“…Another drawback of this approach is that complicated objective lens systems are required to allow for illumination of the lens to be performed at different angles while maintaining constant resolution. 12,13,19 In the approach taken in this study, the objective lens system is mounted to the moveable part of the fiber at a fixed distance from the fiber tip. In this way, the FOV is equal to the lateral stroke of the fiber.…”

“…In most of these approaches, the objective lens system in front of the fiber distal end is not actuated, which results in constraints on the achievable numerical aperture (NA) and the FOV of the scanner. 12,13 Different optical imaging modalities can be employed in a single-fiber optic scanner such as confocal reflectance, 13 confocal fluorescence, 14 two-photon fluorescence, 15,16 and optical coherence tomography. 17,18 Most single-fiber scanning microscopes that have been previously demonstrated operate in resonant modes; as such, they may not be ideal for applications requiring longer acquisition times such as two-photon microscopy and Raman spectroscopy.…”

Achromatic miniature lens system for coherent Raman scattering microscopy

“…Advances in this area can be divided into two categories: objective lens systems that use miniature multi-lens objectives and systems based on the use of gradient refractive index (GRIN) optics. Multi-lens miniature objectives have been used for linear and nonlinear imaging techniques such as confocal reflectance [11][12][13][14][15], two-photon excitation fluorescence (TPEF) [16][17][18][19][20] and CARS. [21,22] Similarly, GRIN lenses have been utilized in confocal reflectance [23], TPEF [24][25][26][27][28] and CRS [29] imaging applications.…”