The paper describes a microcontroller based secured optical wireless communication system using laser and phototransistor. These days the usage of Wi-Fi has reached to every nook and corner of the world. There are some downsides belong to the usage of Wi-Fi such as those concerning to the speed, limited bandwidth, security and range of its usage. In order to overcome these hitches, we can use the advanced version of Li-Fi which is efficient, high speed, and fully networked wireless communication. If light contains encrypted message then both privacy and prevention from unwanted access along with high data rate can be achievable from Li-Fi. A new encryption technique based on substitution of ASCII value of characters implemented and reliable data transmission carried out. The proposed encryption algorithm primarily follows Caesar Cipher WHEEL substitution, acts similarly with Caesar wheel device by rotating circularly and changes the ASCII value of original message according to predefined values and length of repetition. Encryption of data, transmission, reception, and conversion to original message are implemented successfully using laser, phototransistor, and microcontroller and associated devices. The microcontroller performs as overall controlling and processing unit.