Photonics is a breakthrough technology as it uses photons (smallest unit of light) as the data carrier instead of electrons (smallest unit of electricity) used in electronic ICs. As light travels at very high speeds, photonics is widely used to transfer huge amounts of data at a very high speed.Thus photnics based products are primarily deployed in the field of optical fiber & optical free space communications.
Just as Integrated circuit (IC) is a microelectronic device that houses multiple electric circuits on a chip, a photonic integrated circuit (PIC) or Integrated Photonic circuits (IPC) are devices that integrate multiple photonic functions on a chip. A typical IPC may consist of single photon sources, nonlinear photon processing circuits and photon detectors all integrated onto a solid-state chip. Photonic integrated circuits (PICs) have attracted considerable attention owing to their small footprint, scalability, reduced power consumption and enhanced processing stability.
While photonic integrated circuits (PIC) were mostly limited to very specific functions (e.g. transceivers) the technology is slowly finding its way into diverse application spaces. Recently the widespread availability of tunable elements on a photonic chip has given rise to so-called ’programmable’ photonic circuits. In a programmable PIC, the paths of the light are not predefined. Instead, the circuit consists of a mesh of waveguides connected together with 2×2 optical gates, which consist of a tunable 2 × 2 coupler (the on-chip equivalent of a free-space 2 × 2 optical beamsplitter) and a phase shifter (or an equivalent optical subcircuit).
This is supported by rapidly maturing PIC technology platforms in a variety of material systems, such as III-V
semiconductors, silicon, or silicon nitride. Fabricated with similar semiconductor technologies as electronic chips, these PIC platforms support dense integration of 100s or 1000s of optical building blocks on a chip. When these building blocks include electrically tunable elements, the behaviour of the chip can be actively manipulated. As a result, static photonic integrated circuits have gradually become more tunable, where the performance or the functionality can be adjusted at run time. Of course, this requires the integration of the photonic circuit with an electronic driver circuit.
Researchers define two main classes of programmable waveguide meshes. In forward-only meshes the light propagates in one direction from a set of input ports to a set of output ports. The optical gates control how the waveguides are coupled, where the optical fields in the output ports are a linear combination of the fields in the input ports. Such an operation effectively performs a complex matrix-vector multiplication of the amplitudes/phases in the input ports with a matrix determined by the configuration of the mesh. Such operations are especially useful for machine learning algorithms but also for quantum information processing, where the qubits are encoded in the amplitude and phase of single photons propagating through the mesh, write Researchers Wim Bogaerts from Ghent University – IMEC, and others.
While there are different arrangements of forward-only meshes that can be used to construct an arbitrary linear
transformation between the input and output ports, the functionality of a forward-only mesh is inherently limited to the mapping of a preassigned set of input ports onto output ports. More complicated photonic functions, even if they are purely passive, are more difficult to implement: wavelength filters, reflectors or resonators.
The second type of waveguide mesh, called by authors as a recirculating mesh, which overcomes many of these limitations. The waveguides are now arranged in loops connected with the same type of 2 × 2 optical gates. The unit cells of these meshes can be triangular, square or hexagonal, and light can circulate in clockwise or counterclockwise direction. This scheme effectively connects all exposed waveguides on the periphery, so all ports can act as either input or output.
Because of this omnidirectional propagation, recirculating meshes are more flexible in the definition of optical paths. It is possible to implement paths with different optical lengths, which opens the gate to implement interferometric wavelength filters. The waveguide loops themselves can also be used as ring resonators or loop mirrors.
Because all ports can be considered equivalent, it is possible to use them to attach other functional devices to the
mesh, such as high-speed modulators, photodetectors, light sources or other specialized functions such as long, low-loss delay lines. With this scheme, the recirculating mesh can be configured into different circuits connecting these active functions together. This capability, combining programmable connectivity with all the other functions of classical photonic integrated circuits, makes the recirculating meshes a general-purpose programmable PIC technology. For example, a recirculating mesh can be configured as an optical transceiver connecting a modulator and detector to input and output fibers.
Because the mesh also has full phase control, a coherent IQ modulator and coherence receiver can also be constructed, and it is even possible to implement wavelength filters for wavelength division multiplexing. The same filters could be used to implement a sensor readout system or spectrometer. The high-speed modulators and detectors can also be used to translate microwave signals into the optical domain so filtering or frequency conversion can be programmed in the waveguide mesh.
A general-purpose photonic circuit introduces many advantages that we are familiar with from the electronics world. Off-the-shelf availability, together with a software interface, enables fast prototyping of new functionality, and when integrated into products, offer a path for fixes and upgrades. Also, a general-purpose chip can address more diverse markets and therefore be fabricated into larger volumes.
Integrated Photonics Processor Outperforms Wireless Systems
An international team led by researchers at the Politecnico di Milano has devised a way to separate and distinguish optical beams even when the beams are superimposed, and even when the form in which the beams arrive at a destination is drastically changed and/or unknown. In the researchers’ design, the beams were separated in the optical domain and were simultaneously detected with negligible crosstalk — even when they shared the same wavelength and polarization.
The phenomenon is enabled by a programmable photonic processor built on a 5-mm2 chip that receives all optical beams through microscopic optical antennas integrated onto the chip. A network of integrated interferometers manipulates the beams and separates them on distinct optical fibers, which eliminates interference.
The device allowed information quantities of over 5000 GHz to be managed — a value that the research team said is at least 100× that which current high-capacity wireless systems can manage. “A peculiarity of our photonic processor is that it can self-configure very simply, without the need for complex control techniques,” said Francesco Morichetti, head of the Photonic Devices Lab at the Politecnico di Milano. “This allows scalability to new versions of the device, capable of handling many beams at the same time, further increasing the transmission capacity. It is also able to adapt in real time to compensate for effects introduced by moving obstacles or atmospheric turbulence, allowing the establishment and maintenance of optimal optical connections.”
An international collaborations has developed a technique to separate and distinguish optical beams even if they are superimposed and the form in which they arrive at their destination is drastically changed and unknown. The development supports the ability to use on-chip designs in applications including precision positioning and self-driving cars.
Like in optical fibers, light in free space can travel in beams that take different shapes, or modes, with each mode carrying a flow of information. The generation, manipulation, and reception of more modes means more the transmission of more information. However, free space is a more variable environment than an optical fiber, due to atmospheric agents that can alter the shape of light beams or otherwise affect them.
The researchers identified applications that require the advanced processing of free space optics beams: wavefront sensing, phase-front mapping and reconstruction, multiple-beam transmission and imaging through scattering media, and chip-to-chip optical wireless communications. Additionally, high-precision positioning and localization systems, such as self-driving cars, and sensors, remote object detection, portable and wearable devices, and biomedical applications are among those that require the advanced processing of optical beams, the researchers said.
Researchers from Stanford University, the Scuola Superiore Sant’Anna, and the University of Glasgow also participated. The research was published in Light: Science & Applications (www.doi.org/10.1038/s41377-022-00884-8).
iPronics raises €3.7 Million to accelerate the adoption of programmable photonic chips reported in July 2022
iPRONICS, the pioneering photonic computing company that has developed the first general-purpose photonic processor that is reconfigurable by software, today announced a €3.7M investment led by Amadeus Capital Partners, with participation from Caixa Capital Risc. Emerging technology trends in autonomous vehicles and LIDAR, 5G signal processing, deep learning and AI, cyber security, DNA sequencing, and drug discovery require much faster, more flexible, power-efficient computation.
Although advanced electronic chips (e.g. GPUs, TPUs or FPGAs) have increased their capabilities, they still cannot keep up with performance requirements, and today’s hardware has become the bottleneck. Computational photonics (i.e. photonic chips) is becoming the solution because it provides lower latency, lower power consumption (photons/light consume less energy than electrons), higher bandwidth, and higher density.
“We know that photonic computing is the answer to many of the bottlenecks of new killer applications, but designing and building one photonic chip for each of those applications is not practical,” said Prof. Jose Capmany, Fellow of the IEEE and Optical Society of America, and co-founder of iPronics. “Reconfigurability of photonic chips with software is the answer.”
Amelia Armour, Partner at Amadeus Capital Partners, added: “As long term investors in disruptive chip design technology, we are excited to back the team that pioneered the concept of programmable photonics and first demonstrated it in the lab. We look forward to helping the team to bring the chip to market at scale”.
iPronics has introduced a new generation of photonic circuits where common hardware can be programmed using software for a wide variety of applications through a mesh of on-chip waveguides and tunable beam couplers. The reconfigurability of the chip unlocks new commercial applications by delivering faster time to market with lower total cost and risk mitigation while delivering on the promises of photonic processing: lower power consumption and latency, and faster computational speed. It also democratizes the adoption of photonic technology by enabling software engineers without expertise in hardware or photonics.
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