Abstract: The present invention relates to an apparatus and method of making a Dense Wavelength-Division Multiplexer (DWDM) using a Fused-Biconical Taper ("FBT") technique. The DWDM according to the present invention comprises a multiple of Multi-window Wavelength-Division Multiplexers ("MWDMs") which cascade together in several stages, each stage has several MWDMs having an identical window spacing. For a N-channel DWDM, there are 2.sup.m-1 MWDMs cascaded in m-th stage, and the window spacing of the m-th stage MWDMs is 2.sup.m-1 .DELTA..lambda., where m is from 1 to (logN/log2), for example, the first stage (m=1) having 1 MWDM and the window spacing is .DELTA..lambda., the second stage (m=2) having 2 MWDMs and the window spacing is 2 .DELTA..lambda., the third stage(m=3) having 4 MWDMs and the window spacing is 4.DELTA..lambda., etc., and the (logN/log2)-th stage has (N/2) MWDMs with a window spacing (N/2).DELTA..lambda.. The number N could be 2, 4, 8, 16 or more.

Abstract: An improved SRAM cell having ultra-high density and methods for fabrication are described. Each SRAM cell, according to the present invention, has its own buried structure, including word lines (i.e., gate regions) and bit lines (i.e., source/drain regions), thus increasing the cell ratio of channel width of cell transistor to that of pass transistor to keep the data stored in the cell transistor more stable without increasing the area per cell. In addition, according to the present invention, the field isolation between active regions is not field oxide but blankly ion-implanted silicon substrate. Therefore, SRAM cells can be densely integrated due to the absence of bird's beak encroachment. Since the present invention has more planar topography, it is easily adapted to the VLSI process, which is always restricted by the limit of resolution of photolithography, thus increasing the degree of integration.