Development of high-speed LiNb3 optical switch with CMOS driver circuit

“光开关”是改变光信号路径而不进行电光转换的关键器件。在高速光通信中，采用LiNbO_3和半导体器件的外置光开关已经实现了实用化。对于小型网络，即路由器，而不是主网，实现更高速度、更低功耗的光开关仍然有很大的需求。从驱动电路施加的调制电压必须传输到开放式传输线。在本研究中，我们设计了连接到开放式传输线的高速低功耗驱动电路来实现高速光开关。为了实现低功耗，我们采用CMOS逆变器结构作为核心电路，从而得到待机无功耗驱动电路。为了获得LiNbO_3光开关的开关电压，我们将每个nMOS和pMOS场效应管堆叠起来。CMOS逆变器的传输延迟主要取决于负载电容（C_L）和输出电阻（R_<out>），其中C_<out>主要由该电路上MOS的寄生电容组成。C_<out>和R_<out>应设置较小的值，以抑制传播延迟。然而，当栅极宽度增加以获得较小的R_<out>值时，C_<out>增大。为了解决这个问题，我们通过在驱动电路的输出中插入集总电感(L)来补偿C_<out>。然而，在CMOS工艺中，由于螺旋电感在高频范围内的自谐振和杂散阻抗，使得用螺旋电感制造大电感变得困难。因此，我们提出了一种新的方法，通过将栅极宽度分成n级来减小C_<out>和栅极电容，并通过在划分漏极线和栅极线的输出和输入点之间插入具有高特性阻抗的传输线来补偿各电容。从10% V_<out>切换到90% V_<out>的时间为0.0315 nsec，比以前的版本快31.5%。少

"Optical switch" is the key device, which changes the route of optical signal without electro-optic conversion. In the high-speed optical communications, external optical switches using a LiNbO_3 and semiconductor devices have already been operated for practical use. There have still been great needs for realizing higher-speed and lower power optical switch for small networks, i.e., router, rather than main networks. The modulation voltage applied from the driver circuit must be transmitted to the open-ended transmission line. In this resarch, we designed the high speed and low-power driver circuit connected to the open-end transmission line for realizing high-speed optical switch.For realizing the low power dissipation, we adopted the CMOS inverter structure as a core circuit, so that, we obtain the stand-by power less driver circuit. In order to obtain the switching voltage of our LiNbO_3 optical switch, we stacked each nMOS and pMOS FET.The propagation delay of CMOS inverters depend … More s on the load capacitance (C_L) and the output resistance (R_<out>), where C_<out> mainly consists of parasitic capacitance of MOS on this circuit. C_<out> and R_<out> should be small values to suppress the propagation delay. However, when the gate width is increased in order to obtain the small value of R_<out>, C_<out> increases. To solve this problem, we compensated for C_<out> by inserting lumped inductance (L) in the output of the driver circuit. However, in the CMOS process, it is difficult to fabricate large inductance by spiral inductor because of the self-resonance and stray impedances in high frequency range. So, we propose a new method, which decrease C_<out> and gate capacitance by dividing gates width into n stage and compensate each capacitances by inserting transmission lines with high characteristic impedance between the output and input point of the divided drain line and gate line. Switching time from 10% to 90% V_<out> of the distributed type driver is 0.0315 nsec which is 31.5% faster than that of previous version. Less