Technique challenges in coupling of high resolution spectrograph with extremely large telescope

We reviewed the designing of several international ground-based extremely large optical/infrared telescopes and introduced the problems faced in the coupling of high resolution spectrograph with telescopes of extremely large aperture. It is proposed that large area of echelle and ultrafast focal ratio camera can serve as a solution. According to the coupling rule of the spectrogragh and the telescope, the diameter of collimated beam for a 30 m telescope would be over 70 cm, and the size of the main dispersion echelle grating would be larger than 2 m2. To build such huge and costly equipment would be difficult with current techniques. And large aperture camera with focal ratio F/0.5 is also hard to design and manufacture. Image slicer, mosaic gratings and white pupil optic become major solutions in designing the high resolution spectrograph for an extremely large aperture telescope.