Optoelectronic Integration

Aaron KuefferApril 20th, 2020

What are optoelectronics?

Optoelectronics is the study and application of electronic devices that interact with light. Photon emission and absorption in semiconductors are the two main ways these devices are utilized. These can be controlled through clever doping and utilization of refraction and reflection.

These devices include

1. LED2. Photo diodes3. Laser diodes4. Charge-Coupled Devices5. Optical fibers

Light Emitting Diode (LED)

● A LED is a semiconductor diode that emits light when forward biased

● A photon is released when an electron meets a hole and falls to a lower energy level (recombination)

https://en.wikipedia.org/wiki/Band_diagram#/media/File:PnJunction-LED-E.svg

LED cont.

● Color can also be changed based on semiconductor material

● The wavelength of light emitted depends on the band gap of the semiconductor

● Doping can be controlled to raise or lower the desired bandgap

http://www.expertsmind.com/learning/light-emitting-diode-colours-assignment-help-7342873207.aspx

Photodiode● When excited by sufficient energy, a

mobile electron and a hole are created.

● A photodiode can either be a PN junction or a PIN structure

http://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/semiconductor-diodes/images/pnjunctionphotodiode.png

PIN Photodiode● A PIN photodiode has a long central

intrinsic section between the P and N doped regions

● Most photons are absorbed in the intrinsic regions allowing the carriers to more efficiently contribute to the photocurrent

● The fasted PIN photodiodes have bandwidth well above 100 GHz and can have bit rates up to 160 Gbps in optical fibers

● Increased the intrinsic region increases the photodiodes sensitivity

https://www.rp-photonics.com/p_i_n_photodiodes.html

Laser Diodes● Laser diodes offer a stimulated

emission of light with the output being amplified

● This is achieved by generating a gain by flowing an electrical current through the PN junction

● Stimulated emission is induced by a photon of a specific frequency interacts with an excited electron

https://www.artinis.com/blogpost-all/2018/8/13/what-is-the-difference-between-laser-and-led

Laser Diode

● Laser medium is similar to a semiconductor (N and P)

● Mirrors are placed on each end, one highly reflective and another partially

● Allows for a concentrated light output beam with further stimulation by trapping photons

https://www.researchgate.net/figure/A-basic-side-pumped-laser-resonator-setup_fig4_295539597

Charge-Coupled Devices

● These devices move electrical charge to a place they can be manipulated

● CCD devices have applications in things like digital imaging

● They capture incoming photons and convert to electron charges to later allow for reading of these captured charges

● Each pixel captures electrons proportional to the intensity of photon energy at each pixel

Charge-Coupled Devices

● Incoming photons react with the MOS capacitor which generates electron hole pairs

● The charge is then stored in the potential well

Charge-Coupled Devices

● In order to store and read the stored information charges are transferred

● This operates as a shift register until they reach a charge amplifier to convert to a voltage

● This process is repeated to convert the entire content to a series of voltages to be utilized in a digital device https://www.microscopyu.com/digital-imaging/introduction-to-cha

rge-coupled-devices-ccds

Optical Fiber

● An optical fiber is made up of a dielectric waveguide that transmits light through total internal refraction.

● When light signals are sent through the cable they reflect of the core in a zig-zag pattern

● Due to dense glass layers the signal travels 30% slower than the speed of light

https://www.researchgate.net/figure/Total-internal-reflection-in-an-optical-fiber-The-black-light-rays-represent-incident_fig5_267998123

Optical Fiber

● Single mode fibers travel in a straight path down the middle of the core for things like cable TV, internet, and telephone signals.

● Multimode fibers are much larger and offer multiple paths for light to take with different paths. These are used for short distance operations like linking computer networks

● A non communication device example is the gastroscope

Optical Fiber

● Compared to other cables, optical fibers are extremely efficient

● Repeaters only need to be place 80 km-100 km apart because of very low attenuation of signals

● There is no interference from magnetic fields● These fibers are small and lightweight● One pound can transmit information equivalent to 132 metric

tons of copper

Summary

These devices were developed through innovative work because of their large base in theory and quantum mechanics of light. Each device has a important application and can be improved upon for the future. Making these devices cheaper and more efficient will always be of importance.

Referenceshttps://www.degruyter.com/view/journals/nanoph/6/6/article-p1205.xml?tab_body=fullHtml-69327https://www.electronicshub.org/light-emitting-diode-basics/https://www.electronics-tutorials.ws/diode/diode_8.htmlhttp://www.expertsmind.com/learning/light-emitting-diode-colours-assignment-help-7342873207.aspxhttps://www.elprocus.com/photodiode-working-principle-applications/https://www.rp-photonics.com/p_i_n_photodiodes.htmlhttps://www.microscopyu.com/digital-imaging/introduction-to-charge-coupled-devices-ccdshttp://www.mssl.ucl.ac.uk/www_detector/ccdgroup/optheory/ccdoperation.htmlhttps://www.rp-photonics.com/laser_resonators.htmlhttps://en.wikipedia.org/wiki/Charge-coupled_devicehttps://searchnetworking.techtarget.com/definition/fiber-optics-optical-fiberhttps://www.explainthatstuff.com/fiberoptics.html

Key points

● A photon is released when an electron meets a hole and falls to a lower energy level (recombination)

● A photodiode functions a photodetector. When excited by sufficient energy, a mobile electron and a hole are created.

● To get stimulated emission a photon of a specific frequency reacts with an excited electron dropping it to its ground state

● In CCD digital imaging devices arrays of MOS capacitors take in photons to recreate the image

● Optical fibers take advantage of total internal refraction and light to achieve greater capacity for data transmission