Issue Description
We are connecting CE6810-32T16S4Q-LI switch 40G port to our core switch CE6850-48S6Q-HI. However the port is not coming up. Please help us to fix the issue
when connected the access switch to access switch in the same 40 G port it became coming up but when connected to core switch , it’s not coming up
CE6810-32T16S4Q-LI  
Software Version: (CE6810LI V200R005C10SPC800)
Patch Version: V200R005SPH010
Interface: 40G1/0/1
CE6850-48S6Q-HI  
Software Version: (CE6850HI V100R005C00SPC300)
Patch Version: No Patch
Interface: 40G1/0/3
Connection Cable: Multi Mode Fiber optic LC to LC Cable
Transceiver Type: 40GBASE_BIDI

Handling Process
After checking the transceiver type we found the following :
Optical module on the two ends is >> QSFP-40G-SR-BD / 40GBASE-BIDI
his optical module is supported by the two devices in version >> V100R006C00 and later versions
The two devices are :
CE6810-32T16S4Q-LI >> Software Version: (CE6810LI V200R005C10SPC800)
Patch Version: V200R005SPH010
CE6850-48S6Q-HI >> Software Version: (CE6850HI V100R005C00SPC300)

From the previous analysis we can find that the optical module is supported by the two devices with version starting from V100R006C00, How ever the software version on the core switch CE6850-48S6Q-HI is V100R005C00 which does not support this optical module so the software version on the core switch needs to be upgraded to software version V100R006C00 or later versions to support the optical module QSFP-40G-SR-BD / 40GBASE-BIDI

Suggestions
if you face issue of optical interface is down, kindly first thing to check is the tranceiver type and check if it's supported by the device and software or not through the product document as seen in the previous analysis