Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1981-08-14
1985-03-19
Willis, Davis L.
Optics: measuring and testing
By particle light scattering
With photocell detection
350 9614, G01B 902
Patent
active
045055874
DESCRIPTION:
BRIEF SUMMARY
This application is based upon and claims the priority of International Application No. PCT/US81/01086, filed Aug. 14, 1981.
TECHNICAL FIELD
The field of this invention is optical signal processing and, more particularly, very short optical pulse generation.
BACKGROUND ART
In recent years there has been considerable progress in integrated optics technology. Optical devices such as modulators, switches and multiplexers have been successfully fabricated on single substrates of both dielectrics and semiconductors. These devices are rugged, compact and relatively easy to construct. They are also compatible with optical fibers, semiconductor lasers and photodiodes. One such optical device is the Mach-Zehnder interferometeric modulator. In that device, an optical signal in an input optical waveguide is divided into two branches of equal lengths. The signals from the two branches are then recombined in a single-mode output waveguide. By electro-optically varying the index of refraction of one or both of those branches, the relative phase of the light at the end of each branch can be varied. The interference of those two recombined signals results in an output intensity which is dependent on the index of refraction of the controlled branch.
Attention is called to an article entitled "Picosecond Optical Sampling" by the inventors and their colleagues in the IEEE Journal of Quantum Electronics, Vol. QE-16, pp. 870-874, August 1980 and the references cited therein.
There exists a need for a generator of ultra-short optical pulses of regular shape and duration which can produce jitter-free trains of such pulses.
DISCLOSURE OF THE INVENTION
This invention discloses an integrated optical system for generating ultra-short pulses by using sinusoidal microwave fields applied to optical waveguides. The technique exploits the availability of compact microwave oscillators up to 100 GHz and the broad bandwidth achievable in traveling-wave optical switches and modulators. By using a waveguide version of a Mach-Zehnder interferometer and sinusoidally modulating the phase matching via a microwave oscillator in a mode converter biased for 100 percent convertion, convertion will occur only for voltages sufficiently close to zero. To get short samples one must minimize the time the voltage spends near zero; hence, a cascade of microwave driven interferometers operating at a moderate voltage will achieve ultra-short (picosecond) samples.
To permit synchronization of the drive means and to obtain short samples with a long time and no spurious intensity peaks between samples, the following equation can be used: drive means and k is a integer representing the order in the cascade.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a waveguide interferometer and sinusoidal modulator.
FIG. 2 is a schematic diagram of a cascade arrangement of devices like the one shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 a device 10 is shown including an interferometer 12 having an input 20, a first arm 14, a second arm 16 and an output 22. The device 10 also includes a microwave drive means 18. If the amplitude of the microwave drive is adjusted to produce a relative phase shift of transfer from input 20 to output 22 will occur at the zero crossings and no transfer will occur at the peaks (the power which is not transferred is converted to radiation modes rather than being reflected backwards). More precisely, neglecting the transit time of the optical signal, the drive 18 causes the interferometer 12 to have an optical transfer function of ##EQU1## where P.sub.i and P.sub.o are the input and output power envelopes of the optical signal. Note that P.sub.o /P.sub.i is a nonlinear function of the applied voltage so that the optical response is "narrower" than the applied modulation voltage.
In FIG. 2 a cascade 30 of devices such as the device 10, discussed above, is shown. For the general case of a cascade of N devices, the optical response is govern by the following equation: ##EQU2## For a given valu
REFERENCES:
patent: 4070094 (1978-01-01), Martin
Alferness, "Guided-Wave Devices for Optical Communication," IEEE J. of Quant. Electronics, vol. QE-17, No. 6, pp. 946-959, Jun. 1981.
Keil et al., "Mack-Zehucler Waveguide Modulations in Ti-Diffusal LiNbO.sub.3 ", Siemens Forsch u. Entwickl. vol. 9, No. 1, pp. 26-31, Jan. 1980.
Haus et al., "Picosecond Optical Sampling," IEEE J. of Quant. Electronics, vol. QE-16, No. 8, pp. 870-873, Aug. 1980.
Haus Hermann A.
Kirsch Steven T.
Leonberger Frederick J.
Engellenner Thomas J.
Koren Matthew W.
Massachusetts Institute of Technology
Smith, Jr. Arthur A.
Willis Davis L.
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