In this paper, a unique device that can act as both multiplexer and demultiplexer is proposed with two all-metal compensating rods that makes the compensated chip almost the same spectrum profile as the original one. In this way a flat-top athermal arrayed-waveguide grating module of 100-GHz×40-ch is successfully fabricated. A small center wavelength shift of ±25 pm is achieved for the ultra-wide temperature range from -40°C to 85°C with the low insertion loss change of less than ±0.14 dB.