White Paper : Ultra‐wide‐angle optical diffuser for 3D‐ToFsensors in automotive application
Executive Summary
3D sensing systems based on Time of Flight (ToF) is recently becoming more popular due to its
compactness, less stress to CPU, and alsofunctioning even in a dark place. The ToF principle
is based on measuring the time it takes for a wave
to travel from a source (a time‐of‐flight sensor) toan object and back.
Our ”Platanus®" for ToF sensors is a proprietary
optical diffuser that controls light distribution sothat light emitted from a light source is reflectedback into the light‐receiving camera to measure thedistance. This white paper introduces the state of
the art wide horizontal FOI of 140° and its in‐vehicle
applications.

1. Introduction

Fig. 1 Measurement distance, resolution and application
fields of 3D sensing

In the recent advancement of automotive industry especially enhancing safe driving and autonomous
driving brought up the needs to check the status of the driver and passengers. In Europe, it will bemandatory requirement to be equipped with a DMS(Drive Monitoring System) to grant 5‐star safety
rating for the new cars after the year 2023. A schematics of ToF system illustrated in Fig. 2, is used formonitoring 3D information in the vehicle. Pulsed wave of light emitted from a surface emitting laser(VCSEL) through the optical diffuser as Tx module illuminates the objects to be measured. In the lightreceiving section (Rx module), the light reflected from the objects is detected by the camera to calculate
the distance based on the time delay of the returned pulse light to the input pulse.
In limited space budget
inside a car to capture themovement of the driver andpassengers both in the front
and rear seats is thechallenge, The wide‐angle
illumination with a wide‐
angled diffuser is required
to meet this requirement.

2. Thesis Questions
Micro lens array(MLA) is
known as one of theFig. 2 Drive Monitoring System (DMS) with 3D‐TOF)
approaches to diffuse thelight. But there are anumber of drawbacks especially when achieving the wider diffused angle. (Fig. 3)
As we want to achieve the wider angle of diffuser with the low refractive index material, the structure
becomes very steep convexity, as a result, a part of the light incident on the lens is internally reflectedon the opposite side of the lens, resulted the higher intensity at a low exit angle. And it caused theorientation distribution, which is called "bat wing" (from the shape of a bat spreading its wings), where
the intensity is originally stronger at larger angles, won’t be achievable.

SCIVAX | NANOBIC 7‐7 Shin‐Kawasaki, Saiwai‐ku, Kawasaki City, Kanagawa Prefecture 212‐0032 | +81‐44‐599‐5051

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On the other hand, if the high refractive
index material is used, the height of lenscan be lowered and the above‐mentioned
reflection issue can be mitigated, while thelight utilization efficiency is degraded dueto the increase of the Fresnel reflection at
the bottom of the lens.

3. Solutions

Fig. 3 Challenges when using microlens arrays for ultra‐high FOI illumination

We propose the new light diffuser, Platanus® which was designed based on the hybrid optics ofdiffractive and refractive as a solution.
Fig. 4 shows the opticalcharacteristics of the ultra‐wide angle Platanus®,
optical diffuser FOI of 140°× 110°. 140° for the lateral
direction of diffused lightwith the preferred bat wing
shape and high lighttransmission (75%) wasconfirmed. Such higher
efficiency is the uniquefeature of Platanus®
especially in wider diffused
angle.
Fig. 4 Orientation distribution of 140°×110° ultra‐wide‐angle optical diffuser

4. Application for DMS
Fig. 5 shows a 3D image obtained with a
TOF sensor system from MELEXIS, Inc.
using 140° x 110° Platanus® diffuser.
(a)The distance of the sensor with theilluminator from the human’s face wasonly 50cm while it clearly measured theends of stretched arms. (b) Also
demonstrated the capability ofmonitoring both driver and passenger’s
seat with the single diffuser lens.

5. Conclusion
Platanus®, the optical diffuser withFig. 5 3D image measured by a sensor 50 cm away from the subject
wider angle of illumination for ToF(a) Person with outstretched hand (b) Driver’s seat
sensor is applicable for variety of(b) Courtesy of MELEXIS
emerging applications such as
automotive and VR. All of our optical components from SCIVAX are made by the cost efficient
imprinting method. Our Foundry Service provides the design customization, process development, andmass production service with your own customized optical diffuser for various applications.

SCIVAX | NANOBIC 7‐7 Shin‐Kawasaki, Saiwai‐ku, Kawasaki City, Kanagawa Prefecture 212‐0032 | +81‐44‐599‐5051

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