Optical amplifier
They are used as optical repeaters in the long distance fiber-optic cables which carry much of the world's telecommunication links.
The patent covered “the amplification of light by the stimulated emission of photons from ions, atoms or molecules in gaseous, liquid or solid state.”[4] In total, Gould obtained 48 patents related to the optical amplifier[5] that covered 80% of the lasers on the market at the time of issuance.
Huber and Steve Alexander of Ciena invented the dual-stage optical amplifier[7] (U.S. patent 5,159,601) that was a key to the first dense wave division multiplexing (DWDM) system, that they released in June 1996.
[8] Optical amplification WDM systems are the common basis of all local, metro, national, intercontinental and subsea telecommunications networks[9] and the technology of choice for the fiber optic backbones of the Internet (e.g. fiber-optic cables form a basis of modern-day computer networking).
The variety of materials allows the amplification of different wavelengths, while the shape of the medium can distinguish between those more suitable for energy or average power scaling.
[10] Beside their use in fundamental research from gravitational wave detection[11] to high energy physics at the National Ignition Facility they can also be found in many of today's ultra short pulsed lasers.
The amplification window is determined by the spectroscopic properties of the dopant ions, the glass structure of the optical fiber, and the wavelength and power of the pump laser.
In addition, the Stark effect also removes the degeneracy of energy states having the same total angular momentum (specified by the quantum number J).
Thus, for example, the trivalent erbium ion (Er3+) has a ground state with J = 15/2, and in the presence of an electric field splits into J + 1/2 = 8 sublevels with slightly different energies.
A relatively high-powered beam of light is mixed with the input signal using a wavelength selective coupler (WSC).
A significant point is that the erbium gives up its energy in the form of additional photons which are exactly in the same phase and direction as the signal being amplified.
In both methods, attention to effects such as the spontaneous emission accompanying the input signal are critical to accurate measurement of noise figure.
The absorption and emission cross sections of the ions can be modeled as ellipsoids with the major axes aligned at random in all directions in different glass sites.
Gain and lasing in erbium-doped fibers were first demonstrated in 1986–87 by two groups; one including David N. Payne, R. Mears, I.M Jauncey and L. Reekie, from the University of Southampton[15][16] and one from AT&T Bell Laboratories, consisting of E. Desurvire, P. Becker, and J.
[17] The dual-stage optical amplifier which enabled dense wave division multiplexing (DWDM) was invented by Stephen B. Alexander at Ciena Corporation.
However, Ytterbium doped fiber lasers and amplifiers, operating near 1 micrometre wavelength, have many applications in industrial processing of materials, as these devices can be made with extremely high output power (tens of kilowatts).
Recent designs include anti-reflective coatings and tilted wave guide and window regions which can reduce end face reflection to less than 0.001%.
One part has a structure of a Fabry-Pérot laser diode and the other has a tapered geometry in order to reduce the power density on the output facet.
The SOA has higher noise, lower gain, moderate polarization dependence and high nonlinearity with fast transient time.
Given their vertical-cavity geometry, VCSOAs are resonant cavity optical amplifiers that operate with the input/output signal entering/exiting normal to the wafer surface.
In addition to their small size, the surface normal operation of VCSOAs leads to a number of advantages, including low power consumption, low noise figure, polarization insensitive gain, and the ability to fabricate high fill factor two-dimensional arrays on a single semiconductor chip.
Unlike the EDFA and SOA the amplification effect is achieved by a nonlinear interaction between the signal and a pump laser within an optical fiber.
A distributed Raman amplifier is one in which the transmission fiber is utilised as the gain medium by multiplexing a pump wavelength with signal wavelength, while a lumped Raman amplifier utilises a dedicated, shorter length of fiber to provide amplification.
Another advantage of Raman amplification is that it is a relatively broad-band amplifier with a bandwidth > 5 THz, and the gain is reasonably flat over a wide wavelength range.
First, compared to the EDFAs, Raman amplifiers have relatively poor pumping efficiency at lower signal powers.
A third disadvantage of Raman amplifiers is a fast response time, which gives rise to new sources of noise, as further discussed below.
Beta barium borate (BBO)) or even a standard fused silica optical fiber via the Kerr effect.
In contrast to the previously mentioned amplifiers, which are mostly used in telecommunication environments, this type finds its main application in expanding the frequency tunability of ultrafast solid-state lasers (e.g. Ti:sapphire).
By using a noncollinear interaction geometry optical parametric amplifiers are capable of extremely broad amplification bandwidths.
One key enhancement enabling penetration into the scientific market was improvement in high finesse fiber amplifiers, which became able to deliver single frequency linewidths (<5 kHz) together with excellent beam quality and stable linearly polarized output.
