In this article, a new design of the intelligent realtime monitoring and protecting device which is supposed to better adapt to the physical layer protection of the mesh optical network is introduced. The device obeys
the principle of 1+ 1 protection method which is based on the  dual fed selective receiving mode. T he ARM7 series microprocessor ∀∀ ∀ S3C44B0X (with an ARM7T DMI core) is used as the hardware platform of the device, UBoot
( as the boot loader) and the embedded CLinux operation system are transplanted to S3C44B0X as the software platform as well. In the optical structure design of the device, a kind of the M ! N nonblocking optical switch
matrix or the M ! N strict non blocking optical switch and optical combiner array is used to select, receive and retransmit the protecting light signal. T he primary function of the device is implemented by the intelligent realtime
monitoring and protecting application which runs under the embedded CLinux operation system environment. With the algorithm of automatic establishment of the protecting light path, the intelligent real time monitoring and
protecting application establishes the protecting light path in the protection fiber network for each corresponding working light path in advance. And then a protecting light path route table will be dynamically established and
maintained by each device. During the establishment of the protecting light paths, devices communicate with each other by using T CP/IP protocol. And after the accomplishment of the protecting light path establishment, the
protecting light path route table of one device will be broadcasted to all the other devices. By means of converting the optical signal into the electric ones, the real time optical power of the working light paths is monitored by the
device. As soon as the fault of the working light path occurs, the device will switch to the corresponding protecting light path immediately. In the end of this article, the algorithm of automatic establishment of the protection light
path is assumed to be implemented in a 4 node mesh optical network, and the emulation result is given. The device
proposed in this article is a kind of real unattended intelligent real ?time monitoring and protecting device, which is suitable for the physical layer protection of mesh optical network. So by applying the proposed intelligent realtime
monitoring and protecting device, the transparent uninterrupted communication of mesh optical network could be achievable in the way of the full optical protection.