Endoscope Flashcards
Bundles of optical fibres are described as either coherent or non-coherent.
Describe how the fibres are arranged in each type of bundle and explain how the different designs determine their optical characteristics.
In a coherent bundle fibres are maintained in fixed positions relative to each other whereas in a non-coherent bundle fibres have no fixed relative positions. This means that a coherent bundle can be used to tranmit images mage up of light energy whereas non-coherent ones just transfer the light energy and image transfer is not possible.
Bundles of optical fibres are described as either coherent or non-coherent.
State an application for each type of bundle.
Coherent bundles of fibres can be used to transmit images of internal organs of the body so a doctor can ‘see’ inside a patient.
Non-coherent bundles can be used to transmit (or conduct) light to the inside of the human body. This illuminates the site that the doctor wishes to view.
Give two advantages of a bundle consisting of fibres of very small diameter over a bundle consisting of larger fibres.
High resolution (fine detail) images can be seen if the fibres are of small diameter. The bundle would also be more flexible than if thicker fibres were used. The fine fibres would also allow bending around tighter curves without light escaping.
Give two reasons why a glass cladding is used around the central core of each fibre in a coherent bundle.
Scratches on the outer surface would allow light to escape - the cladding protects the outer surface.
Close contact between adjacent fibres (or liquid penetrating between fibres) would allow light to pass from one fibre to another, the cladding ensures that image is not confused (corrupted, scrambled) - it prevents light passing between individual fibres.
State and explain whether the following changes in the optical fibre would increase or decrease the probability of light escaping from the fibre.
increasing the refractive index of the cladding
A smaller difference between the core index and cladding index makes the critical angle largertherefore increases the chance of light escaping
State and explain whether the following changes in the optical fibre would increase or decrease the probability of light escaping from the fibre.
bending the fibre into a tighter curve
This makes the internal angle of incidence at core-cladding interface more likely to be less than the critical angle
therefore increases the chance of light escaping
State and explain two physical properties of the light produced by a laser which makes it different from the light produced by a filament lamp.
Laser light is monochromatic. It is composed of waves of single frequency/wavelength, whereas the light from a lamp consists of a range of wavelengths.
Laser light is collimated. An approximately parallel beam is produced. A lamp produces light that spreads out in all directions from the source.
Laser light is coherent - waves produced are in constant phase with each other; whereas light from a filament lamp is incoherent.
An endoscope may use light from a filament lamp and light from a laser. State the use of the light from a filament lamp,
To illuminate the inside of a body - such incoherent light can be sent down the light guide
An endoscope may use light from a filament lamp and light from a laser. State a use of the light from a laser
Cauterising - stopping bleeding/cutting tissue/treatment of tumours
An endoscope contains two bundles of optical fibres.
Name the two bundles. For each bundle state clearly the arrangement of the fibres and explain its purpose in the operation of the endoscope.
In the coherent bundle the fibres retain the same relative position to each other at both ends of the cable. The coherent cable transfers images from inside of body to the viewer.
In the non-coherent bundle of fibres there is no relative order to the fibres. The non-coherent bundle simply works as a light guide. It carries light into body/for illumination purposes.
In the optical system of a flexible endoscope there are two types of fibre bundles, coherent and non-coherent. Explain the purpose of each of these two types of bundle
Use of non-coherent to transmit light into body/ provide illumination
Use of coherent to transmit image/ light to form an image (from inside to viewer/camera)
