optical encoding with photodiodes optical encoding with photodiodes

Optical encoding with photodiodes

What are optical rotary encoders?

Optical rotary encoders use a pattern of light-and-dark, or on/off signals of light, to detect rotation angles and the position of an object for applications such as robotics, machine control, motion control, web process control, and motor feedback.  An optical rotary encoder has a code wheel (with fine-pitch windows or slits) a light emitter such as an LED, and a photosensor such as a photodiode.  These components can be arranged in two configurations:  transmissive and reflective.  As the code wheel rotates, it creates different light patterns for the photodiode to detect, indicating the encoder's movement and position.


High accuracy detection of the light pattern requires a photodiode that can detect complicated patterns at high speed and an LED whose irradiation is uniform.  We offer such photodiodes and LEDs for optical rotary 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

FOP mounting

It is possible to mount a Hamamatsu fiber optic plate (FOP) to the photosensitive area of a Si photodiode. Combining an FOP and Si photodiode allows the lens to focus at a position that is higher by the amount of the FOP thickness than the normal photosensitive surface. This makes it easier to mount a slip plate or other components closer to the photosensitive surface. Moreover, the photosensitivity directivity can be adjusted by using an FOP with a low NA.

Example: FOP

FOP directivity

Example: Si photodiode with an FOP

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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