Lens free Imaging:
Lens-free on-chip imaging refers to using a digital optoelectronic sensor array, such as a charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) chip to directly sample the light transmitted through a specimen without the use of any imaging lenses between the object and the sensor planes. ….The advancements in this type of microscopy are being spearheaded by the development of sensor chips that are continually being improved and introduced into consumer electronics products, particularly cell phones and high-end digital cameras.For a lens-free on-chip microscope, there are various design choices that one can select from. ….In general we can categorize bright-field lens-free microscopes into two main streams: (i) contact-mode shadow imaging–based microscopes and (ii) diffraction-based lens-free microscope….
Key components of lens-free holographic on-chip microscopy
In a partially coherent holographic on-chip microscope the source can simply be an LED or an array of LEDs. In case wavelength tunability is desired, a monochromator can also be used that is coupled to a multimode fiber. The spectral bandwidth of the source can vary from a few nanometers to 20–30 nm depending on the sample-to-detector distance and the resolution requirement of the system. Because the sample plane is close to the detector plane (typically ≤0.1–2 mm), the scattered light rays and the background light can still interfere at the sensor chip even though the temporal coherence lengths of such broadband sources are significantly shorter than those of lasers.
Greenbaum et al, Nature Methods, Vol 9, pp 889–895, (2012)