Optical modulators using semiconductor nano-structures
An
Electro-optic modulator of nano-structures
An electro-optic modulator is a device which can be used for controlling the power, phase or polarization of a laser beam with an electrical control signal. It typically contains one or two
The crystal which is covered by electrode may be considered to be a voltage-variable wave-plate. When a voltage is applied, the retardation of laser polarization of the light would be changed while a beam passes through an ADP crystal. This variation in polarization results in intensity modulation downstream from the output polarizer. The output polarizer converts the phase shift into an amplitude modulation.
Micrometre-scale silicon electro-optic modulator[3]
This device was fabricated a shape of the p-i-n ring resonator on a
Acousto-optic modulator of nano-structures
Acousto-optic modulators are used to vary and control laser beam intensity. A Bragg configuration gives a single first order output beam, whose intensity is directly linked to the power of RF control signal. The rise time of the modulator is simply deduced by the necessary time for the acoustic wave to travel through the laser beam. For highest speeds the laser beam will be focused down, forming a beam waist as it passes through the modulator.
In an AOM a laser beam is caused to interact with a high frequency ultrasonic sound wave inside an optically polished block of crystal or glass (the interaction medium). By carefully orientating the laser with respect to the sound waves the beam can be made to reflect off the acoustic wave-fronts (
Acoustic
Acoustic
Magneto-optic modulator of nano-structures
A dc magnetic field Hdc is applied perpendicular to the light propagation direction to produce a single domain, transverse directed 4~Ms. The rf modulation field Hrf, applied by means of a coil along the light propagation direction, wobbles 4~Ms through an angle of @ and produces a time varying magnetization component in the longitudinal direction. This component then produces an ac variation in the plane of polarization via the longitudinal Faraday effect. Conversion to amplitude modulation is accomplished by the indicated analyzer.
Wideband magneto-optic modulation in a bismuth-substituted yttrium iron garnet waveguide[5]
The current transient creates a time-varying magnetic field that has a component along the direction of optical propagation. This component (underneath the microstrip line) acts to tip the magnetization, M, along the propagation direction of the optical beam. A static in-plane magnetic field, by, is applied perpendicular to the light propagation direction, thus ensuring the return of M to its initial orientation after the passage of the current transient. Depending on the component of the magnetization along the z-direction, Mz, the optical beam experiences a rotation of its polarization due to the Faraday effect. The polarization modulation is converted into an intensity modulation via a polarization analyzer, which is detected by a high-speed photodiode.
Other semiconductor nanostructures of optical modulator
MODULATION OF THz RADIATION BY SEMICONDUCTOR NANOSTRUCTURES[6]
As a result of increased demand for bandwidth, wireless short-range communication systems are expected to extend into the THz frequency range. Therefore, the fundamental interactions between THz radiation and semiconductors are receiving increasing attention. This new quantum structure is based on the well-established technology for producing high electron mobility transistors where an electron gas is confined at a GaAs/AlxGa1 xAs interface. The electron density at the hetero-interface can be controlled by the application of an external gate voltage, which in turn will alter the transmission/reflection characteristics of the device to an incident THz beam.
Applications and Commercial products
Electro-optic modulator
- from THORLABS
40 Gbit/s Phase Modulator The 40 Gbit/s Phase Modulator is a high performance, low drive voltage External Optical Modulator designed for customers developing next generation 40G transmission systems. The increased bandwidth allows for chirp control in high-speed data communications.
Applications ; Chirp Control for High-Speed Communications (SONET OC-768 Interfaces, SDH STM-256 Interfaces), Coherent communications, C & L Band Operation, Optical Sensing, All-optical frequency shifting.
- from Mach-40
Acousto-optic modulator of nano-structures
Applications ; acousto-optic modulators include laser printing, video disk recording, laser projection systems.
- from ELECTRO-OPTICAL PRODUCTS CORPORATION
References
- ^ Sadagopan, T., Choi, S. J., Dapkus, P. D. & Bond, A. E. Digest of the LEOS Summer Topical Meetings MC2–-3 IEEE, Piscataway, New Jersey (2004)
- ^ Liu, A. et al. Nature 427, 615–618 (2004)
- ^ Nature 435, 325–327 (19 May 2005)
- ^ Journal of Physics: Conference Series 92 (PHONONS 2007)
- ^ Optics Communications Volume 220, Issues 4–6
- ^ MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 35, No. 5, December 5, 2002