OCT is a noninvasive, high-resolution optical imaging technology capable of real-time imaging of tissue microanatomy with a few millimeter imaging depth and can be envisioned as an optical analog of ultrasound B-mode imaging, except that it utilizes near infrared light rather sound waves. Compared to ultrasound, OCT does not require a matching gel and the resolution of OCT can be 50-100 times finer than ultrasound. OCT can thus function as a form of “optical biopsy”, capable of assessing tissue microanatomy and function with a resolution approaching that of standard histology but without the need for tissue removal. The axial resolution of OCT is governed by the spectral bandwidth of the light source and it is inversely proportional to the source spectrum bandwidth. Chromatic aberration in the OCT imaging optics will alter the backreflected spectrum from the target, resulting in the loss of OCT axial resolution. The change in the backreflected spectrum from the sample could also result in the increase in the side lobes of the OCT imaging signal, which again will lead to the loss of OCT axial resolution. In addition, as in conventional imaging optics, the chromatic aberration will focus light of different colors to different spots, thus degrading the OCT lateral resolution as well. In a benchtop imaging system such as a microscope, chromatic aberration in the imaging optics is routinely corrected by using achromatic lenses (e.g. lenses made of multi elements with different refractive index profiles and surface curvatures). But, such approaches are not cost effective or practical to be implemented in miniature OCT imaging probes.
Miniature endoscopes are a critical component in the OCT technology, enabling translational applications for imaging internal luminal organs such as the gastrointestinal tract or airways. Most OCT endoscopes developed so far were designed for imaging at 1300 nm, which provides 2-3 mm imaging depth and 8-30 μm axial resolution. However, there is an increasing need to develop an ultrahigh-resolution OCT endoscope for resolving fine structures (e.g. under 5 μm) such as airway smooth muscle or structural changes associated with early stage diseases. Benefiting from the availability of broadband light sources at 800 nm, ultrahigh-resolution OCT imaging has been demonstrated at such wavelength with bench-top systems. For the endoscopic setting, due to the challenges such as management of chromatic aberration over a broadband spectral bandwidth, there are only few achromatic endoscopic setups. The designs in those endoscopes are rather complicated and expensive, involving multi-element achromatic microlenses.
Accordingly, there is a need in the art for a miniature OCT device and a cost-effective and practically implemented method for color corrected OCT imaging.