Abstract
We present an index profile design for remarkably low loss multimode optical crossed waveguide. In this paper, we theoretically calculate the light propagation loss in crossed waveguides with step-index (SI) and graded-index (GI) square cores utilizing a ray tracing simulation. In this simulation, we focus on the index exponent values for the GI profile, which allows low crossing loss even if the number of crossing is as large as 50 or even if the crossing angle is as low as 20°. It is revealed that an index exponent of 2.0 for the GI core strongly contributes to exhibit 35 times lower loss (0.072 dB after 50-perpendicular crosses) compared to the loss of the SI-core counterpart (2.58 dB after the same crossings). The GI cores with a smaller index exponent exhibit better loss in crossed waveguides with a wide range of crossing angles from 30° to 90°. Furthermore, we discuss the effect of the refractive index profile at the intersection on the optical loss of crossed waveguides.
Highlights
The performance gain of microprocessors has been accelerating the arithmetic processing speed of high performance computers (HPCs), which has led to a worldwide performance competition amongst HPCs [1]
Optical printed circuit board (PCB) (O-PCBs) have been a promising solution to realize on-board optical interconnects, by which wiring density much higher than multimode fiber links mentioned above can be realized
We have demonstrated that multimode polymer waveguides with graded-index (GI) core show lower loss, lower interchannel crosstalk, and lower connection loss with multimode optical fibers with a circular GI core [8,9,10]
Summary
The performance gain of microprocessors has been accelerating the arithmetic processing speed of high performance computers (HPCs), which has led to a worldwide performance competition amongst HPCs [1]. Some HPCs with greater than peta FLOPS performance already have adopted multimode optical fiber (MMF) links for their rack-to-rack data exchanges, where optical/electrical (O/E) and E/O signal conversions take place at the edge of a printed circuit board (PCB). The O/E and E/O conversions are required to be very close to the processor chips, because the signal distortion in the on-board electrical wiring (even in such a short link) should be reduced for further high-speed and power-efficient operations [2]. GI-core polymer waveguides have been drawing attention [11, 12] It has not yet been discussed how the index profile, a very important characteristic of GI-core contributes to low-loss waveguides. The loss at the intersection in the crossed cores is theoretically calculated using a ray-trace simulation
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