Photonic Integrated Circuit

Photonic Integrated Circuit Technology

Photonic Integrated Circuit (also known as PIC), is a complex integrated circuit which incorporates a lot of optical devices to form a single photonic circuit. The main difference between a PIC and an Electronic IC is that PIC is analogous to an Electronic Integrated Circuit.  Many optical devices like optical amplifiers, multiplexers, de-multiplexers, optical lasers, attenuators and also detectors are integrated on to a Photonic Integrated Circuit. For a large-scale operation of such a device thousands of optical devices will be integrated on to the device.

In a PIC, the signals are sent by superimposing them on wavelengths usually in the range between the visible spectrum and infrared. The range usually is between 800 nanometers and 1700 nanometers.

In 2005, during a development of a laser light through silicon in an electronic integrated circuit, there occurred a problem with quantum noise, which prevented the generation. This problem was easily overcome by a photonic integrated circuit, which easily created the laser light and that too in a higher bandwidth, within the circuit as a single medium. Thus the importance of PIC was known.

Photonic Integrated Circuits vs Electronic Integrated Circuits

The main difference between PIC and Electronic Integrated Circuits is in the type of material that is used for its fabrication. In the case of an electronic IC, the most dominant material that is used is silicon. But, in the case of PIC, the fabrication material mainly depends on the purpose of the device. That is the material will depend on the function that is to be integrated by the device. The most common materials that are used for its fabrication are a mixture of silica on silicon, silicon on insulator, and so on. Apart from these mixtures even some types of polymers and semiconductor materials are also used to make lasers like which are used to make semiconductor lasers such as Gallium Arsenide [GaAs] and Indium Phosphide [InP].

Take a look at a GaAs-InP Photonic integrated circuit.

IMAGE CREDIT

The fabrication methods for both the devices are the same. Photolithographic methods for etching and deposition of material are the same.

The difference is in the primary device that is used for fabrication. In an electronic integrated circuit the main device is the transistor. But, in PIC, there is no particular main device that dominates in the fabrication. According to its application, the ranges of fabrication devices are different as the devices that are to be integrated are more than that used in an electronic integrated circuit. The devices ranges from optical amplifiers, filters, low loss-high efficiency interconnect waveguides, detectors, power splitters, modulators and lasers. As different materials are required to fabricate all these devices on a single chip, the procedures and steps become very difficult.

But lately researchers have developed methods to make PIC’s using resonant photonic interferometry process. Through this method, we can easily develop ultra violet light emitting diodes (LED) in a cost efficient way. With the use of such LED’s we can easily overcome optical computing problems.

To know more about Light Emitting Diodes, click on the link below.

TAKE A LOOK : WORKING OF LIGHT EMITTING DIODES (LED)

To know more about Photolithography and IC fabrication techniques, click on the link below.

TAKE A LOOK : PHOTOLITHOGRAPHY

TAKE A LOOK : IC FABRICATION TECHNIQUES

Photonic Integration Methods

There are mainly two types of photonic integration methods. They are

• Hybrid Photonic Integration and
• Monolithic Photonic Integration

In the case of Hybrid Photonic Integration, the developed integrated IC will be a single package. This package will consist of a number of photonic devices which is used for the same function. Due to this advantage, a lot of IC’s are made through this method so as to combine a lot of integrated optic devices.

In the case of Monolithic Photonic Integration, a lot of optical devices of different functions are combined together to form a single IC. The manufacture of such a device is difficult as the fabrication materials required will be numerous. All these materials have to be fabricated to construct and integrate into a common substrate. Thus, a number of functions can be done on a single chip.

Applications of Photonic Integrated Circuits

• It is used in fibre-optic communication to make Externally Modulated Lasers (EML) which has a combination of a distributed feedback laser diode and an electro-absorption modulator on a single Indium-Phosphide [InP] chip.
• It has a great application in wavelength division multiplexed (WDM) fiber-optic communication system, where an arrayed waveguide grating (AWG) has to be developed using this technology. AWG is commonly used as optical multiplexers and de-multiplexers.
• Used in biomedical and photonic computing
• Used in Optical sensors and metrology

Advantages of Photonic Integrated Circuits

• The use of optical devices makes the whole system more discrete, compact, and also helps in providing a high performance.
• The chip can also be integrated with basic electronic circuits which makes it applicable for more functions.
• Though rare, PIC’s may be affected due to neutron flux effect and thus cause a loss in some of its functions. But there will not be any problems like electronic IC’s when it comes to effects of electromagnetic pulse [EMP].

Future

The development of this technology has not yet reached its high end. Through constant research, people are trying to make this technology a common, low cost, and highly efficient one. But, in future it is sure that almost all electronic IC’s will be replaced by PIC. There may also be cases where the integration of both electronics and optics will be possible.

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