Application potential of ultra-small VCSEL* reflective photosensors

~Using VCSEL light-emitting devices in the form of "dots" to achieve ultra-small, highly directional detection solutions~

Reflective photoelectric sensors are sensors that use the reflection of light to detect the presence of an object, and their applications are very wide. They are increasingly used in products that are closely related to our daily lives, such as wearable devices. However, if they are to be used more conveniently in areas such as industrial equipment, reflective photoelectric sensor products with higher accuracy and faster response speed are required. Generally speaking, reflective photoelectric sensors are mostly used for switching purposes, but if their characteristics can be used more effectively, there is great potential for the application of such devices. This article will introduce the latest information on this optical device and explore its future development prospects.

*Vertical Cavity Surface Emitting Laser.

In the past, it was mostly used in the communications field, but in recent years it has also been used as a light source for light-emitting units in sensing systems.

1. What is a reflective photoelectric sensor?

Reflective photoelectric sensors are devices that use the reflection of light and are mainly used to detect position. Usually, this type of device is used for switches. In recent years, due to the impact of the COVID-19 pandemic and other factors, the market demand for applications that do not require contact during operation has continued to expand. In our daily lives, there are more and more applications such as thermometers that can measure body temperature without contact, faucets that can dispense water as long as you reach out, and zero-contact elevator buttons. The core devices of these applications are reflective photoelectric sensors.

In addition, reflective photoelectric sensors are also widely used in applications such as smartphones and wearable devices. For example, the proximity detection function can be used to control the screen on and off of the mobile phone's LCD screen; the removal detection function can be used to detect the wearing and removal of wearable devices; and the sensors can be switched between on and off.

2. Application of reflective photoelectric sensors in industrial equipment

In the field of industrial equipment, reflective photoelectric sensors are also beginning to show their prowess. In the past, simple mechanical switches or magnetic switches were usually used to control on and off in switch applications. However, in recent years, with the improvement of automation and unmanned operation of industrial equipment, reflective photoelectric sensors with excellent performance and support for high-performance equipment have begun to emerge.

Compared with mechanical switches and magnetic switches, reflective photoelectric sensors have a smaller package size, so if a switch function needs to be installed in a small or narrow position, or if an object detection function needs to be installed in a narrow place or a place with almost no space, reflective photoelectric sensors can fully demonstrate their advantages.

In addition, there are two types of optical switches: digital switches and analog switches. Although analog switches are difficult to operate, they have the advantage of high design flexibility, while digital switches have limited design flexibility but have the advantage of simple operation.

3. Reflective photoelectric sensors have many applications other than switches

The application of reflective photoelectric sensors is not limited to the single purpose of "switches". Through design creativity, they can also be used in a wider range of fields, so the development potential is very large. For example, reflective photoelectric sensors are widely used in applications and equipment for measuring pulse and heart rate by taking advantage of the property of hemoglobin in the blood that absorbs ultraviolet rays. In addition, since reflective photoelectric sensors can respond to the reflection of light, they can be used to detect "black/white" in addition to "presence/absence". In the industrial field, reflective photoelectric sensors are also used in applications such as motor rotation detection.

4. New applications of reflective photoelectric sensors pioneered by ROHM

Conventional reflective photoelectric sensors usually use LEDs as light-emitting devices. However, ROHM uses its own VCSELs, which consume less power than LEDs and have better directivity, as light-emitting devices, and also uses its own digital output photoelectric ICs as light-receiving devices, and has successfully developed the ultra-small reflective photoelectric sensor "RPR-0720".

① Features of RPR-07201 VCSEL

The biggest feature of the reflective photoelectric sensor "RPR-0720" is that it uses VCSEL as a light-emitting device. Generally speaking, VCSELs are mostly used in large equipment such as automotive applications, so it is difficult to buy low-power VCSELs. ROHM took advantage of its ability to produce VCSELs independently and successfully developed a low-power VCSEL that is very suitable for reflective photoelectric sensors by using VCSEL light-emitting devices in the form of "points" rather than "surfaces". Its light does not diverge like LEDs, so higher detection accuracy can be achieved compared to previous reflective photoelectric sensors.

In addition, by optimizing the module consisting of a VCSEL with a narrower beam divergence angle and a photoelectric IC, the product size has been greatly reduced. Compared with previous reflective photoelectric sensors that use LEDs as light-emitting devices, the packaging area of ​​the new product has been reduced by about 78%.

② RPR-0720 feature 2 No boost circuit required

The voltage range supported by previous reflective photoelectric sensors is usually 2.9V to 3.6V, and a boost circuit and a buck circuit are required. However, ROHM's reflective photoelectric sensors use VCSELs, which have a wider driving range and support a voltage range of 2.7V to 4.5V, so there is no need to configure a boost circuit.

This not only makes the reflective photoelectric sensor itself smaller, but also reduces the number of peripheral components used for boosting, thereby further saving space. It is precisely because of these characteristics that ROHM's reflective photoelectric sensor products can support the use of lithium-ion batteries (2.7V), making them very suitable for wearable devices and small electronic devices that require wear-off detection.

5. Application of VCSEL reflective photoelectric sensors in industrial equipment

In addition to wearable devices, ROHM is also actively studying the use of this ultra-small reflective photoelectric sensor using VCSEL in the field of industrial equipment to replace traditional mechanical switches and magnetic switches.

For example, in scenarios such as detecting objects in narrow locations or limited spaces, detecting the rotation of motors, etc., by using ROHM's ultra-small reflective photoelectric sensors, it is possible to meet detection needs that were not possible in the past, or further improve the convenience of traditional detection methods.

At present, in addition to the digital RPR-0720, ROHM is also developing new analog products to further improve the product system and meet the diverse needs of customers.