Optical computing promises to play a major role in hardware chips dedicated to artificial intelligence (AI). Digital electronics, when employed in computing hardware, face the sunset of Moore’s law and the acknowledged end of Dennard Scaling (energy density of shrinking transistors). In response to these limitations, a paradigm shift towards nondigital processing is on the horizon. In optical computing devices for AI, the dominant mathematical operation is vectormatrix multiplication. It is typically limited to very small vector and matrix sizes. Most approaches don’t allow for significant scaling. In this context, our work focuses on the development of a silicon photonics tensor core that exhibits a unique scalability feature, enabling effective expansion to accommodate large matrix sizes. This scalability is deemed essential for the realization of meaningful AI accelerator products leveraging photonic hardware.
In this work, we discuss the requirements and challenges of designing a photonic computing chip that can be deployed in the latest commercial AI systems. Silicon Photonics have the potential to revolutionize AI computing by delivering unprecedented improvements in the power consumption and computational throughput of AI computations. Still, there are several challenges to be tackled. Among these are the need to design high-density photonic integrated circuits, designing photonic memory systems for data storage, and solving the bottleneck of the electrical-to-optical conversions. Several innovative photonic technologies have been introduced to address these challenges. The progress on implementing these technologies is discussed.
A point source interferometer (PSI) is a device where atoms are split and recombined by applying a temporal sequence of Raman pulses. During the pulse sequence, an initially trapped cloud of cold atoms is released and allowed to expand, behaving approximately as a point source. The PSI can work as a sensitive multi-axes gyroscope that can automatically filter out the signal from accelerations. The phase shift arising from rotations is proportional to the momentum transferred to each atom from the Raman pulses. Therefore, by increasing the momentum transfer, it should be possibly to enhance the sensitivity of the PSI. Here, we investigate the degree of enhancement in sensitivity that could be achieved by augmenting the PSI with large momentum transfer (LMT) employing a sequence of many Raman pulses with alternating directions. Contrary to typical approaches used for describing a PSI, we employ a model under which the motion of the center of mass of each atom is described quantum mechanically. We show how increasing Doppler shifts lead to imperfections, thereby limiting the visibility of the signal fringes, and identify ways to suppress this effect by increasing the effective, two-photon Rabi frequencies of the Raman pulses. Considering the effect of spontaneous emission, we show that for a given value of the one-photon Rabi frequency, there is an optimum value for the number of pulses employed, beyond which the net enhancement in sensitivity begins to decrease. For a one-photon Rabi frequency of 200 MHz, for example, the peak value of the factor of enhancement in sensitivity is ~39, for a momentum transfer that is ~69 times as large as that for a conventional PSI. We also find that this peak value scales as the one-photon Rabi frequency to the power of 4/5.
Fiber ring laser gyroscopes (FRLGs) are among the most sensitive rotation sensors. Recently, we have proposed a scheme for improving the sensitivity of such gyroscopes significantly by using the fast light effect. The resulting device, called the active fast light fiber-optic sensor (AFLIFOS), makes use of a pair of counter-propagating superluminal Brillouin lasers in a fiber cavity. Compared to a conventional FRLG, the sensitivity of the AFLIFOS is expected to be enhanced by nearly four orders of magnitude. For both conventional FRLG and the AFLIFOS, the overall sensitivity increases with increasing output power. However, when the power of the pump laser used for producing the Brillouin gain exceeds a threshold value, cascaded higher order Brillouin lasing may occur, thus complicating the dynamics of the AFLIFOS, and limiting the maximum achievable sensitivity. We experimentally study the parameters that determine the onset of second- and third-order Brillouin lasing in a fiber cavity. We also analyze how the pump power affects the AFLIFOS operation and show how the measured threshold for second-order Brillouin lasing sets a practical limit for the AFLIFOS sensitivity.
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