Endoscope Light Guide

Endoscopes are often used for minimally invasive surgery. They are a combination of a camera and a light guide attached to a long flexible tube.

When a light ray encounters a boundary of a material with an index of refraction that is lower than the index of refraction of its core, it is bent. This process is called refraction and is governed by Snell’s law.

Optical Fibers

An endoscope light guide consists of optical fibers that transmit light from an external light source. These fibers are inserted into the body’s passageways to allow doctors to examine the interior of the body. Optical fibers are flexible and transparent, and they have a diameter that is about the size of a human hair.

Optical fibers can be made from various materials, such as glass and plastic. Depending on the application, these fibers may be single-mode or multimode. In both cases, the number of modes in an optical fiber is determined by the wavelength and refractive index of the core.

The core of an optical fiber is a thin glass section that allows light to travel through it. The outer layer of the fiber, called cladding, reflects light back into the core. The endoscope light guide cladding is often coated with a plastic coating to protect it from moisture and damage.

There are different types of optical fibers, including step-index, graded-index, and plastic-optical fibres. These types of fibres are used in a variety of applications, including remote sensing and transmission of electrical signals.

A step-index fibre consists of a core surrounded by a cladding that has a single uniform refractive index. It can be used to transfer energy from an external light source, such as a laser or a laser diode.

In contrast, a graded-index fibre consists of a core that has a gradient in its refractive index. The refractive index decreases as the radial distance from the fibre axis increases, which makes it ideal for long-distance transmission of information.

When using an optical fiber in an endoscope, it is important that the light enters and exits the core of the fibre at the same angle as the central axis. This is known as total internal reflection, and it allows the light to travel through the fibre without loss.

This technique is extremely useful in many surgical procedures, such as knee surgeries and hand surgery. It also allows doctors to examine the amnion and foetus during pregnancy.

Optical scanners are essential for performing 3-D imaging in an endoscope, as they produce a large amount of light that is able to illuminate the body’s internal organs. Optical scanners can be designed with a variety of scanning methods, including raster, spiral, Lissajous, circular, and propeller patterns. These scans can be performed at different actuation frequencies, which helps to reduce the effects of motion artifacts and to increase the resolution of the scanner.

Adaptors

Optical endoscopes usually require an external source of illumination light to illuminate areas which are located in cavities or in regions that are devoid of natural light. This can be done using small and portable light sources, or larger standalone devices which are positioned to condense illumination light beams towards a predetermined position. These light handles are normally connected to an endoscope body through adaptors.

However, it has been observed that connection of light guides with a numerical aperture different from the one of the light source could lead to numerous problems such as increased light losses in transmission and a restricted or narrow illumination range. In addition, irregularities in the illumination light level across an irradiated intracavitary region may also occur.

In order to address this problem, an adaptor for adjusting the light condensing angle of a light source, which is arranged to condense illumination light beams towards an optically aligned position, into agreement with a numerical aperture of a light guide to be connected to the light source for the purpose of creating optimum conditions in transmitting illumination light to and through the light guide and in projecting the illumination light through an endoscope toward an intracavitary region under observation has been proposed.

According to the invention, an adaptor is removably fitted on a fore end portion of a light guide rod which extends on the part of a manipulating head assembly down to an illumination window at a distal end of an insertion rod of an endoscope. It is plugged into a connector socket at a connection port of a light source to locate a light pickup end face of the light guide rod at a light condensing position of a condenser lens on the part of the light source.

A light source 10 of the present invention comprises a source lamp 11, reflector mirror 12 and condenser lens 13. As explained in more detail below, the condensing angle of the source lamp, reflector mirror and condenser lens is determined by the characteristics of their component materials. In addition, the light source 10 is adapted to supply illumination light at a condensing angle smaller than a maximum acceptance angle of a light guide which is fitted on the part of the manipulating head assembly and extended through a complex flexible cable and down to an illumination window at the distal end of the insertion rod of an endoscope.

Connectors

There are several types of connectors in an endoscope light guide. Some of them are used to connect the light guide to the light source, while others are used for fluid and electrical connection. These connectors are designed to ensure that the endoscope remains stable during operation and to reduce the amount of stress on the endoscope.

Generally, connectors in an endoscope light guide include a light guide rod, a contact pin fitting and a liquid inlet member. In addition, some endoscopes are fitted with a water jet nozzle for introducing liquids into the scope and providing a water blast for clearing lenses or securing the suction tube to operate.

When a light guide is fitted to an endoscope, the angle of incident illumination light rays from the light source to the light pickup end face is determined on the basis of a numerical aperture of the light guide. In case the light guide has a numerical aperture different from that of the light source, an adaptor pipe with a concave lens is fitted on the light guide to adjust the angle of incident illumination light rays into agreement with the numerical aperture of the light source so that the transmission losses of the input illuminating light rays at the light pickup end face are minimized.

The light guide is extended, on one side of a manipulating head assembly of the endoscope, through an insertion rod portion with a light emitting end face at its fore output end located in an illumination window at the distal end of the insertion rod and, on the other side of the manipulating head assembly, through a flexible complex cable.

The flexible complex cable is extracted from the light guide rod and inserted into a connector socket at a connection port of the light source to locate a light pickup end face of the light guide at a light condensing position of a condenser lens of the light source. An adaptor with a concave lens is fitted at a stage anterior of the light pickup end face to adjust the angle of incident illumination light reflected by the condenser lens into agreement with a numerical aperture of the light guide which determines the maximum acceptance angle of the light guide. The adjustment of the angle of incident illumination light reflected by a condenser lens in this way can lead to improved optical performance by reducing the transmission losses of input illuminating light rays.

Power Supply

A power supply in an endoscope light guide is a device that provides electricity to components of the scope. The components include the CCD 48 and other elements that are provided in the tip 40T of the scope for insertion into the body of a subject. A battery is preferably provided, a rechargeable lithium ion battery. The battery is arranged inside the scope and is charged by electromagnetic coupling with the exterior of the scope.

In a typical endoscope, the scope is inserted into the body of a subject to view a body part S. The light emitted by the light source 62 is endoscope light guide used to illuminate the subject’s body part S. The illuminating light is then transmitted to the CCD 48 and other components in the tip 40T of the scope for use by the processor 60.

The illuminating light can be generated using an electrical power source in the tip 40T of the scope for inserting into the body of the subject, or it can be generated from an external source by attaching an electronic component such as a peltier device 16 to the tip of the scope for supplying the illuminating light to the CCD 48 and other components. The peltier device may be a silicon-based device, such as a thermistor.

Alternatively, the illuminating light may be generated from an LED (light-emitting diode), which can produce a wide range of colors. This type of light is typically referred to as cold-light or LED-light.

This type of LED-light can be adapted to different brightness levels and can be controlled by an integrated control circuit. The control circuit can be incorporated into the light source or can be separate and attached to the endoscope handle.

Some illuminating light sources, such as a halogen lamp or a xenon lamp, are not able to supply sufficient illuminating light for the imaging of a subject’s body part S, because they cannot be shaped to fit the endoscope’s scope tube. Fortunately, the light emitted by LEDs can be shaped to fit a variety of scopes, and therefore they are more suitable for illuminating an imaging body part S.