These days, everyone is talking about that Nvidia, AMD, and Intel have invested in a factory to end copper interconnection. In fact, Ayarlabs has been established for a long time, and Intel has been one of its investors for long. What is new is the joining of NVIDIA.
AyarLabs
NVIDIA is concerned about two things: one is the micro-ring modulator, which can realize WDM with low power consumption, and the other is the miniaturized modulator that supports micro-ring cascading, which requires a multi-wavelength light source. Ayarlabs’ technology just meets the requirements of these two. Let’s talk a little bit about Ayarlabs’ technology. One is a laser component called SuperNova, which can achieve multi-wavelength output. Another component called TeraPhy can achieve optical I/O fan-out of more than Tbps.
Let’s talk about SuperNova’s laser first. This year, it has entered the second generation of light sources. It uses 16 lasers with different wavelengths through 16×16 wavelength distribution to achieve 16 optical fibers, each with 16 wavelength outputs. The first generation used 8×8 technology more frequently.
Let’s look at this component from two perspectives.
The laser uses Sliver’s CW DFB, AlGaInAs quantum well active material, and RWG’s waveguide structure. The wavelength distributor adopts the star distribution principle of the Rowland circle structure to achieve 8×8 or 16×16 wavelength scheduling.
As for the TeraPhy part, which converts the “electrical” input and output of the integrated circuit, that is, I/O, into optical signals to realize optical I/O. This integrated circuit can be a GPU or other signals and the key is signal conversion.
Ayarlabs uses silicon photonics integration technology to achieve signal conversion. 3D packaging technology, an embedded interconnection process called EMIB developed by Intel, is used between the silicon photonics integrated chip and the main integrated circuit chip,. This EMIB uses a dense pin to make a “shallow hole” and “short interconnection” between the high-speed signal of the integrated circuit and the high-speed signal in the silicon photonic integrated chip.
The reason for making a shallow holes is that silicon is a semiconductor, and the through holes in silicon will have a parasitic capacitance that produces high-frequency resonance. The use of shallow hole technology can increase the frequency and achieve high-speed design.
Making short interconnection is because the loss of electrical signals increases at high frequencies. Reducing the interconnection distance reduces the loss and improves the signal quality of the transmission channel. The interconnect packaging of high-frequency signals is very expensive, but some low-speed signals, such as power supply and control signals, can be processed using low-cost ordinary processes, which achieves compatibility between cost and performance.
Now let’s take a look inside the silicon photonic chip that converts photoelectric signals. A micro-ring modulator is used to realize the output of electrical signals to optical signals, and to realize the input of optical signals and its conversion into electrical signals and send them to the GPU. The SuperNova multi-wavelength light source is provided for use by the modulator. The modulator cannot emit light, but can only complete the electro-optical conversion of the signal. Ayarlabs’ modulator uses a micro-ring structure of silicon photonic material. The micro-ring is wavelength-sensitive, and the wavelength drift coefficient of silicon at different temperatures is large, so a heater is needed for temperature control to avoid wavelength drift of the silicon micro-ring modulator.
There are two major categories of micro-ring modulators. One category is based on the refractive index control of the ring, which realizes the refractive index control through the PN carrier depletion type plasma dispersion effect. The other is based on coupling coefficient. AyarLabs has studied these two technologies. The receiving end is also a micro-ring structure, whose cascade has the ability to automatically identify wavelengths and realize WDM DeMUX wavelength separation. Since microring technology is used for both transmission and reception, Ayarlabs has also done a lot of research on the coupling between the signal waveguide and the microring.
How to distribute the cross-coupling coefficient and the through-coupling coefficient between the waveguide and the ring is related to the trade-off between modulation and output. In addition, the length of the coupling arm is related to the operating bandwidth, which is also a technical detail that needs to be considered.