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Optical encoding
with photodiodes
What are optical rotary encoders?
There are two types of optical rotary encoders: transmissive type and reflective type. In the transmissive type, a code wheel engraved with fine slits is fitted between a light emitter and a photosensor. This type of encoder detects the rotation angle from the on/off signal made by transmitting/blocking light. In the reflective type, the light emitter and the photosensor are placed on the same plane as the code wheel. This type detects the rotation angle from the reflection/non-reflection of light.
To ensure a highly accurate encoder, the light emitter must have the ability to emit light uniformly. Also, the photosensor must have a high-speed response, as well as a chip arrangement that supports complicated slit patterns.
Hamamatsu can provide light emitters and photosensors for both transmissive type and reflective type encoders.
See below to learn more about our photodiodes. Click here to learn more about our LEDs for optical encoders.
Features of photodiodes for encoders
Unique semiconductor process
Using our unique semiconductor process technology, we manufacture high sensitivity, low noise, highly reliable photodiodes that are suitable photosensors for encoders. We also have a proven track record of manufacturing numerous industrial photodiodes.
Designed for optimum sensitivity
We can manufacture photodiodes with high sensitivity for the wavelength of the light source to be used, from visible light to infrared light. A higher signal-to-noise ratio can be expected by optimizing the photodiode's sensitivity for the LED used in the optical encoder.
Extensive mounting technology
We supply products in various package types for many applications including automotive, industrial and consumer. We can offer a wide variety of mounting solutions, including miniature photodiode packages and a single package combining an LED and photodiode.
Examples of special processing applied to Si photodiodes (customization)
Through-hole formation (MEMS processing)
Through-holes can be formed on Si photodiode chips by applying MEMS technology. This allows a confinement type LED used in reflective encoders and the like to be mounted inside the hole of a Si photodiode chip. Further, the chip's thickness can be adjusted to align the height of the LED emitter to that of the photosensitive area of the Si photodiode.
Example: through-hole
Example: LED is mounted inside a through-hole of a Si photodiode
Low-reflectance, light-shielding film
The reflectance of metal wiring and components other than the photosensitive area can be reduced by applying a light-shielding film to the surface of the Si photodiode through special processing. Improvement to the signal-to-noise ratio can be expected.
Reflectance vs. wavelength (reference value)
The reflectance of near-infrared light often used in optical encoders is reduced significantly.
Example: Si photodiode with a light-shielding film
Recommended products
Photodiodes for encoders
Silicon photodiodes and fiber optic mounting plate for encoders.
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