optical encoding with photodiodes optical encoding with photodiodes

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.

Transmission encoder | Reflective encoder

Features of photodiodes for encoders

Unique semiconductor process

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

wavelength showing 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

components with 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.

special processing applied to Si photodiodes - example through-hole formation

Example: through-hole

Example: LED is mounted inside a through-hole of a Si photodiode

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) graph

Reflectance vs. wavelength (reference value)
The reflectance of near-infrared light often used in optical encoders is reduced significantly.

Si photodiode with a light-shielding film

Example: Si photodiode with a light-shielding film

Recommended products

Photodiodes for encoders

Silicon photodiodes and fiber optic mounting plate for encoders.

Contact us for more information.

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