RSoft Enewsletter

April 2017

OptSim Circuit: Simulation of AIM Photonics Transmitter-Receiver and Generation of Masks

The time for large-scale, reliable photonic integrated circuits (PICs) has finally arrived. In addition to the favorable economics from higher energy efficiency, smaller footprint and lower cost, photonic integration is recognized as essential to national security. The role of photonic design automation (PDA) tools, including OptSim Circuit [1], is going to be as indispensable to PICs as was (and still is) the role of electronic design automation (EDA) tools to the fruition of Moore’s law for CMOS over the last 50 years.

This tip illustrates the simulation of photonic integrated circuits (PICs) in OptSim Circuit based on components using the AIM Photonics PDK by Analog Photonics [2] and generation of masks via the interface to the layout tools [3]. The project file can be supplied, upon request, to the customers of OptSim Circuit version 2017.03 and above.

A typical migration path from idea to fabrication is shown in Figure 1 below.

migration path

Figure 1. A high-level view of the steps involved in moving from idea to PIC realization.

The topology of Figure 2(a) simulates the back-to-back transmission and detection of a 15-Gbps NRZ signal using transmitter and receiver PICs.

The transmitter is based on a Mach-Zehnder Modulator driven in a push-pull fashion, with the drive waveform for the top MZM arm modulated between -2.66 and -1.66 V, and the bottom arm modulated between 0 and -1 V. The drive waveforms have 10-to-90% rise-fall times of approximately 4 ps. The compound component (CC) aimTX contains the AIM PDK-based transmitter design, depicted in Figure 2(b), and consists of Si edge couplers, waveguides, and an MZM.

15-Gbps NRZ signal

(a)

AIM PDK-based transmitter design

(b)

AIM PDK-based receiver

(c)

Figure 2. (a) Top-level topology for simulating the AIM-based transmitter and receiver
(b) Transmitter PIC (c) Receiver PIC.

The AIM PDK-based receiver, shown in Figure 2(c), is contained in the CC aimRX, and contains a Si edge coupler, waveguide, and Ge photodetector.

For the complete design, the initial 0 dBm cw source incurs a total optical loss of approximately -17 dB as can be seen in the signal summaries at various ports after the simulation. The transmitter PIC loss is approximately -14.3 dB, while the receiver PIC loss is approximately -2.7 dB. The average loss of the MZM, taking into account both insertion loss and modulation, is approximately 8.8 dB.

Figure 3 depicts the eye diagram at the photodetector output, whose average current is approximately 17.2 µA. The extinction ratio of the received eye diagram is approximately 6 dB. The bitrate can be increased to 20 Gb/s without inducing any degradation in extinction ratio. At a bitrate of 25 Gb/s, the extinction ratio is expected to be around 5 dB which can be increased by driving with 1.2 Vpp electrical signals.

Photodetector current eye diagram.

Figure 3. Photodetector current eye diagram.

Once the design is optimized in OptSim Circuit to meet or exceed the desired performance goals, the next step is to create a mask for fabrication at the foundry. As an illustration, let’s consider the transmitter PIC schematic of Figure 2(b).

In order to create a PDAFlow netlist, use “Utilities” menu of the OptSim Circuit GUI [4]. Once the netlist is generated, it can be opened in the mask layout tool OptoDesigner to view corresponding mask. Figure 4 shows top view of the mask.

mask

Figure 4. Mask for the schematic of Figure 2(b).