Editing Photonics (section)

==Overview of photonics research==
The science of photonics includes investigation of the [[emission (electromagnetic radiation)|emission]], transmission, [[amplifier|amplification]], detection, and [[modulation]] of light.

===Light sources===
Photonics commonly uses semiconductor-based light sources, such as [[light-emitting diode]]s (LEDs), [[superluminescent diode]]s, and lasers. Other light sources include [[single photon sources]], [[fluorescent lamp]]s, [[cathode-ray tube]]s (CRTs), and [[plasma screen]]s. Note that while CRTs, plasma screens, and [[organic light-emitting diode]] displays generate their own light, [[liquid crystal display]]s (LCDs) like [[TFT screen]]s require a [[backlight]] of either [[cold cathode fluorescent lamp]]s or, more often today, LEDs.

Characteristic for research on semiconductor light sources is the frequent use of [[III-V semiconductor]]s instead of the classical semiconductors like [[silicon]] and [[germanium]]. This is due to the special properties of [[III-V semiconductor]]s that allow for the implementation of [[light source|light emitting device]]s. Examples for material systems used are [[gallium arsenide]] (GaAs) and [[aluminium gallium arsenide]] (AlGaAs) or other [[compound semiconductor]]s. They are also used in conjunction with silicon to produce [[hybrid silicon laser]]s.

===Transmission media===
Light can be transmitted through any [[transparency and translucency|transparent]] medium. [[Optical fiber|Glass fiber]] or [[plastic optical fiber]] can be used to guide the light along a desired path. In [[optical communication]]s optical fibers allow for [[transmission (telecommunications)|transmission]] distances of more than 100&nbsp;km without amplification depending on the bit rate and modulation format used for transmission. A very advanced research topic within photonics is the investigation and fabrication of special structures and "materials" with engineered optical properties. These include [[photonic crystal]]s, [[photonic crystal fiber]]s and [[metamaterial]]s.

===Amplifiers===
{{Main|Optical amplifier}}
Optical amplifiers are used to amplify an optical signal. Optical amplifiers used in optical communications are [[erbium-doped fiber amplifier]]s, [[semiconductor optical amplifier]]s, [[Raman amplifier]]s and [[optical parametric amplifier]]s. A very advanced research topic on optical amplifiers is the research on [[quantum dot]] semiconductor optical amplifiers.

===Detection===
[[Photodetector]]s detect light. Photodetectors range from very fast [[photodiode]]s for communications applications over medium speed charge coupled devices ([[Charge-coupled device|CCDs]]) for [[digital camera]]s to very slow [[solar cell]]s that are used for [[energy harvesting]] from [[sunlight]]. There are also many other photodetectors based on thermal, [[Photographic plate|chemical]], quantum, [[photoelectric]] and other effects.

===Modulation===
{{main|Optical modulator}}
Modulation of a light source is used to encode information on a light source. Modulation can be achieved by the light source directly. One of the simplest examples is to use a [[flashlight]] to send [[Morse code]]. Another method is to take the light from a light source and modulate it in an external [[optical modulator]].<ref>{{cite journal |last=Al-Tarawni |first=Musab A. M. |date=October 2017 |title=Improvement of integrated electric field sensor based on hybrid segmented slot waveguide |journal=Optical Engineering |volume=56 |issue=10 |pages=107105  |doi=10.1117/1.oe.56.10.107105|bibcode=2017OptEn..56j7105A |s2cid=125975031 }}</ref>

An additional topic covered by modulation research is the modulation format. [[On-off keying]] has been the commonly used modulation format in optical communications. In the last years more advanced modulation formats like [[phase-shift keying]] or even [[orthogonal frequency-division multiplexing]] have been investigated to counteract effects like [[dispersion (optics)|dispersion]] that degrade the quality of the transmitted signal.

===Photonic systems===
Photonics also includes research on photonic systems. This term is often used for [[optical communication]] systems. This area of research focuses on the implementation of photonic systems like high speed photonic networks. This also includes research on [[optical regenerator]]s, which improve optical signal quality.{{citation needed|date=April 2013}}

===Photonic integrated circuits===
{{main|Photonic integrated circuit}}
Photonic integrated circuits (PICs) are optically active integrated semiconductor photonic devices. The leading commercial application of PICs are optical transceivers for data center optical networks. PICs fabricated on III-V [[indium phosphide]] semiconductor wafer substrates were the first to achieve commercial success;<ref name="KaminowLi2013">{{cite book|author1=Ivan Kaminow|author2=Tingye Li|author3=Alan E Willner|title=Optical Fiber Telecommunications Volume VIA: Components and Subsystems|url=https://books.google.com/books?id=8V8LMI9WhGEC|date=3 May 2013|publisher=Academic Press|isbn=978-0-12-397235-4}}</ref> PICs based on silicon wafer substrates are now also a commercialized technology.

Key Applications for Integrated Photonics include:
* Data Center Interconnects: Data centers continue to grow in scale as companies and institutions store and process more information in the cloud. With the increase in data center compute, the demands on data center networks correspondingly increase. Optical cables can support greater lane bandwidth at longer transmission distances than copper cables. For short-reach distances and up to 40&nbsp;Gbit/s data transmission rates, non-integrated approaches such as [[vertical-cavity surface-emitting laser]]s can be used for optical transceivers on [[multi-mode optical fiber]] networks.<ref name="Frank2018">{{cite book|author=Chang, Frank|title=Datacenter Connectivity Technologies: Principles and Practice|url=https://books.google.com/books?id=ooIstAEACAAJ|date=17 August 2018|publisher=River Publishers|isbn=978-87-93609-22-8}}</ref> Beyond this range and bandwidth, photonic integrated circuits are key to enable high-performance, low-cost optical transceivers.
* Analog RF Signal Applications: Using the GHz precision signal processing of photonic integrated circuits, radiofrequency (RF) signals can be manipulated with high fidelity to add or drop multiple channels of radio, spread across an ultra-broadband frequency range. In addition, photonic integrated circuits can remove background noise from an RF signal with unprecedented precision, which will increase the signal to noise performance and make possible new benchmarks in low power performance. Taken together, this high precision processing enables us to now pack large amounts of information into ultra-long-distance radio communications. {{Citation needed|date=July 2018}}
* Sensors: Photons can also be used to detect and differentiate the optical properties of materials. They can identify chemical or biochemical gases from air pollution, organic produce, and contaminants in the water. They can also be used to detect abnormalities in the blood, such as low glucose levels, and measure biometrics such as pulse rate. Photonic integrated circuits are being designed as comprehensive and ubiquitous sensors with glass/silicon, and embedded via high-volume production in various mobile devices. {{Citation needed|date=July 2018}} Mobile platform sensors are enabling us to more directly engage with practices that better protect the environment, monitor food supply and keep us healthy.
* [[LIDAR]] and other [[phased array]] [[imaging]]: Arrays of PICs can take advantage of phase delays in the light reflected from objects with three-dimensional shapes to reconstruct 3D images, and Light Imaging, Detection and Ranging (LIDAR) with laser light can offer a complement to [[radar]] by providing precision imaging (with 3D information) at close distances. This new form of [[machine vision]] is having an immediate application in driverless cars to reduce collisions, and in biomedical imaging. Phased arrays can also be used for free-space communications and novel display technologies. Current versions of LIDAR predominantly rely on moving parts, making them large, slow, low resolution, costly, and prone to mechanical vibration and premature failure. Integrated photonics can realize LIDAR within a footprint the size of a postage stamp, scan without moving parts, and be produced in high volume at low cost.<ref>{{cite book  |last1=Notaros |first1=Jelena |title=Imaging and Applied Optics Congress 2022 (3D, AOA, COSI, ISA, pcAOP) |chapter=Silicon Photonics for LiDAR, Augmented Reality, and Beyond |date=11 July 2022 |pages=CM4A.3 |doi=10.1364/COSI.2022.CM4A.3 |url=https://opg.optica.org/abstract.cfm?uri=COSI-2022-CM4A.3 |publisher=Optica Publishing Group |isbn=978-1-957171-09-8 |language=EN}}</ref><ref>{{cite book |last1=Bhargava |first1=P. |last2=Kim |first2=T. |last3=Poulton |first3=C. V. |last4=Notaros |first4=J. |last5=Yaacobi |first5=A. |last6=Timurdogan |first6=E. |last7=Baiocco |first7=C. |last8=Fahrenkopf |first8=N. |last9=Kruger |first9=S. |last10=Ngai |first10=T. |last11=Timalsina |first11=Y. |last12=Watts |first12=M. R. |last13=Stojanovic |first13=V. |title=2019 Symposium on VLSI Circuits |chapter=Fully Integrated Coherent LiDAR in 3D-Integrated Silicon Photonics/65nm CMOS |date=June 2019 |pages=C262–C263 |doi=10.23919/VLSIC.2019.8778154 |isbn=978-4-86348-720-8 |url=https://ieeexplore.ieee.org/document/8778154}}</ref>

=== Biophotonics ===
{{main|Biophotonics}}
'''Biophotonics''' employs tools from the field of photonics to the study of [[biology]]. Biophotonics mainly focuses on improving medical diagnostic abilities (for example for cancer or infectious diseases)<ref>{{Cite journal|last1=Lorenz|first1=Björn|last2=Wichmann|first2=Christina|last3=Stöckel|first3=Stephan|last4=Rösch|first4=Petra|last5=Popp|first5=Jürgen|date=May 2017|title=Cultivation-Free Raman Spectroscopic Investigations of Bacteria|journal=Trends in Microbiology|volume=25|issue=5|pages=413–424|doi=10.1016/j.tim.2017.01.002|issn=1878-4380|pmid=28188076}}</ref> but can also be used for environmental or other applications.<ref>{{Cite journal|last1=Wichmann|first1=Christina|last2=Chhallani|first2=Mehul|last3=Bocklitz|first3=Thomas|last4=Rösch|first4=Petra|last5=Popp|first5=Jürgen|date=5 November 2019|title=Simulation of Transportation and Storage and Their Influence on Raman Spectra of Bacteria|journal=Analytical Chemistry|volume=91|issue=21|pages=13688–13694|doi=10.1021/acs.analchem.9b02932|issn=1520-6882|pmid=31592643|s2cid=203924741 }}</ref><ref>{{Cite journal|last1=Taubert|first1=Martin|last2=Stöckel|first2=Stephan|last3=Geesink|first3=Patricia|last4=Girnus|first4=Sophie|last5=Jehmlich|first5=Nico|last6=von Bergen|first6=Martin|last7=Rösch|first7=Petra|last8=Popp|first8=Jürgen|last9=Küsel|first9=Kirsten|date=January 2018|title=Tracking active groundwater microbes with D2 O labelling to understand their ecosystem function|journal=Environmental Microbiology|volume=20|issue=1|pages=369–384|doi=10.1111/1462-2920.14010|issn=1462-2920|pmid=29194923|bibcode=2018EnvMi..20..369T |s2cid=25510308}}</ref> The main advantages of this approach are speed of analysis, [[non-invasive]] diagnostics, and the ability to work [[in-situ]].