Technology Background: HT - Designs at the “Sweet Spot”
VPH transmission grating technology offers for a given wavelength two grating frequencies where theoretically the diffraction efficiency of both ‘s’ (TE) and ‘p’ (TM) polarized light can simultaneously reach 100%.
At 1545 nm these grating frequencies are 940 lines/mm and 1350 lines/mm.
The UltraSpec™-HT940 and the UltraSpec™-HT1350 are designed at these grating frequencies respectively. This is why they offer minimized PDL and earn the HT designation.