WO2002025321A2 - High speed optical gain flattener - Google Patents

Abstract

A novel intelligent, all optical, high speed, single and multichannel, bulk acoustic optic, dynamic gain flattener. The input fiber optic light source (1) which may be either polarized or unpolarized light is coupled via a lens (2) into two cascaded acousto optic medium (3). The light interacts with the sound wave generated by the piezo-electric acoustic transducers (4) to create three or more light beams from each acousto-optic medium (3). The zero order undeflected light beam and two deflected first order beam, and sometimes even higher order beams. The undeflected zero order beam is coupled back into the output optical fiber (5) via lens (2).

Description

TITLE: High Speed Optical Gain Flattener INVENTORS: Jolanta I. Rόsemeier and Ronald G. Rosemeier

This application is entitled to, and claims the benefit of, priority from U.S. Provisional Application Serial No. 60/234,076, filed September 20, 2000.

FIELD AND BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates in general to optical networks and in particular to a new and useful device and method for flattening or custom changing the optical response across the optical wavelength band of a fiber optic network transmission line.

.Background Information

The invention described and claimed herein comprises a novel intelligent, all optical, high speed, single and multichannel, bulk acousto optic and integrated optic surface acoustic wave, adaptable, dynamic gain flattening filter and/or monitoring control loop system for fiber optic communication 'networks, useful for flattening or custom changing optical response across the optical wavelength band inside a fiber optic network transmission line caused by the different response characteristics of the lasers, fibers, detectors, dynamic add/drops, cascaded amplifiers, optical components, fiber optic amplifiers and other components of the network.

The purpose of the invention is to provide an intelligent, all optical, accurate, stable, high performance, high speed, active, adaptable, dynamic gain flattening filter based upon bulk acousto optic and integrated optic .surface acoustic wave device configurations optically coupled with input and output fibers. Also, by coupling the adaptive gain flatteners with a spectrometer or monitor sensor, and a closed loop control system an intelligent, adaptive, gain flattening system is created which will flatten or custom change the optical response over the entire fiber transmission line. Such devices are, useful for smoothing the output of the present erbiun doped fiber ctmplifiers and future based optical fiber amplifiers in optical fiber optic communication network applications, as well as flattening or custom changing the optical response of an entire fiber transmission line. The problems solved by this invention include an intelligent, all optical, improved, real time, adaptive, gain flattening in fiber optic network communication systems to enhance overall transmission integrity and performance.

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RF frequency deflects out only a portion of the corresponding optical wavelength or in another configuration the light is mode converted and the remaining wavelengths reside in the main optical light beam thus flattening or custom changing the optical response.

It is an object of the invention to provide a dynamic gain flattener which is faster and more reliable than conventional systems'.

It is a further object of the invention to provide an acousto-optical gain flattening system.

A principal feature of the invention is bulk acousto-optic gain flattening.

An intelligent, high speed, optical, gain flattening filter comprising of input and output fibers optically coupled to both a bulk acousto optic device with a piezoelectric transducer which is activated at a single or multiple radio frequencies (RF) which satisfy the requirement of flattening or custom changing the optic response across the optical transmission band in a fiber optic transmission line. In this arrangement the incoming light can be randomly polarized and the device is polarization insensitive.

An intelligent, high speed, optical, gain flattening filter comprising of input and output fibers optically coupled to a bulk acousto optic device with a piezoelectric transducer which is activated at a single or multiple radio frequencies (RF) . This adaptive, acousto optic gain flattening device assembly satisfy the• requirement of flattening or custom changing the optic response across the optical transmission band in a fiber optic transmission line. In this arrangement the incoming light can be randomly polarized and the device is polarization insensitive.

Coupling a spectrometer or monitor in line with the bulk acousto optic gain flattener with a feedback control creates a closed loop control system that automatically flattens or custom changes the optical response across the fiber transmission line.

Coupling a spectrometer or a monitor sensor with the bulk acousto optic gain flattener with a feedback^' control can set flattening values or custom values of the gain flattener device in the network line and then can be removed. As transmission network system conditions change the spectrometer can be reconnected to reset values of adaptive gain flattener and then removed.

An intelligent, high speed, optical, gain flattening filter comprising of input and output fibers optically coupled to a multi channel array of piezoelectric transducers on a bulk acousto optic device or devices which are activated at a single or multiple radio frequencies (RF) . This adaptive, acousto optic gain flattening multi channel device assembly satisfy the requirement of flattening or custom changing the optic response across the optical transmission band in a fiber optic transmission line. In this arrangement the incoming light can be randomly polarized and the device is polarization insensitive.

An intelligent, high speed, optical, gain flattening filter comprising of input and output fibers optically coupled to an integrated optic surface acoustic wave device utilizing a planar optical waveguide whereby single or multiple radio frequencies RF is coupled in the interdigital transducers to satisfy the requirement of gain flattening or custom changing the optical response across the optical transmission band in ^'a fiber optic transmission line. In this arrangement the incoming light can be randomly polarized and the device is polarization insensitive.

An intelligent, high speed, optical, gain flattening filter comprising of input and output fibers optically coupled to an integrated optic surface acoustic wave device utilizing optical mode conversion whereby single or multiple radio frequencies RF is coupled in the interdigital transducers to satisfy the requirement of gain flattening or custom changing the optical response across the optical transmission band in a fiber optic transmission line .

Coupling a spectrometer or a monitor sensor in line with the integrated optic surface acoustic wave device to gain flatten utilizing a planar waveguide with a feedback control creating a closed loop control system that automatically flattens or custom changes the optical response across the fiber transmission line.

Coupling a spectrometer or a monitor sensor in line with the integrated optic surface acoustic wave device to gain flatten utilizing optical mode conversion with a feedback control creating a closed loop control system that automatically flattens or custom changes the optical response across the fiber transmission line.

Coupling a spectrometer or a monitor sensor with the integrated optic surface acoustic wave device to gain flatten or custom change the response utilizing a planar waveguide with a feedback control^" can set the values of the gain flattener device in the network line and then can be then be removed. As transmission network system conditions change the spectrometer or monitqr sensor can be reconnected to reset values of adaptive gain flattener and then removed. Coupling a spectrometer or a monitor sensor with the integrated optic surface acoustic wave device to gain flatten or custom change the response utilizing optical mode conversion with a feedback control can set the values of the gain flattener device in the network line and then can be then be removed. As transmission network system conditions change the spectrometer can be reconnected to reset values of adaptive gain flattener and then removed.

Coupling a detector and/or detectors at the +1 and/or 1 diffracted order beams from the various described bulk gain flattening devices while the fiber transmission line is optically coupled to the zero order beam of the gain flattening or custom response changing device, and with RF energies coupled into the transducer and now by monitoring the detector response as a function of wavelength for example, a spectrometer or monitor sensor is created from the same bulk acousto optic device configurations. Hence, by supplying feedback from a control circuit to the gain flattening or custom changing device assemblies and by changing the RF power and RF frequency to flatten or custom change the optical response in the transmission line, the same device which is used as a gain flattener and/or custom response changer is now used as a self monitoring and self controlling device .

Similarly coupling detectors to the integrated optic surface acoustic wave devices with feedback control circuits make them act as both gain flattener and/or custom response changers as well as self monitoring and self controlling devices, as they are optically coupled in and out of the fiber transmission line.

These and other objects, features and advantages which will be apparent from the discussion which follows are achieved, in accordance with the invention, by providing a novel intelligent, ' all optical, high speed, single and multichannel, bulk acousto optic and integrated optic surface acoustic wave, adaptable, dynamic gain flattening filter and/or monitoring control loop system for fiber optic communication networks, useful for flattening or custom changing optical response across the optical wavelength band inside a fiber optic network transmission line caused by the different response characteristics of the lasers, fibers, detectors, dynamic add/drops, cascaded amplifiers, optical components, fiber optic amplifiers and other components of the network.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its advantages and objects, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated. BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and still other objects of this invention will become apparent, along with various advantages and features of novelty residing in the present embodiments, from study of the following drawings, in which:

Figure 1 is a Schematic of bulk Acousto optic gain flattening filter with two cascaded optical media.

Figure 2 is a Schematic of bulk acousto optic gain flattening filter with two cascaded optical media and folded optical path.

Figure 3 shows a Multichannel bulk acousto optic gain flattening filter with folded optical path.

Figure 4 shows a Multichannel bulk acousto optic gain flattening filter with folded optical path using coupled optical fibers and prisms.

Figure 5 is a Schematic of bulk acousto optic gain flattening filter with detectors and folded -optical path.

Figure 6 shows a Multichannel bulk acousto optic gain flattening filter ^• with detectors and folded optical path.

Figure 7 shows a Multichannel bulk acousto optic gain flattening filter with detectors and folded optical path using coupled optical fibers and prisms.

Figure 8 shows the Application of adaptive gain flattening in fiber optic transmission line with automatic closed loop feedback control utilizing a spectrometer near the gain flattening device.

Figure 9 shows the Application of adaptive gain flattening with automatic closed loop feedback control utilizing a spectrometer positioned remotely to flatten transmission line response.

Figure 10 illustrates an Integrated optic surface acousto wave gain flattening device constructed on planar optical waveguide to optically flatten the response in a transmission line.

^• Figure 11 illustrates an Integrated optic surface acousto wave gain flattening device constructed on lightparent piezoelectric substrate with appropriate embedded waveguide structure to change the response of the optical transmission line. Figure 12 shows the Application of adaptive .gain flattening or custom changing device in fiber optic transmission line with automatic closed loop feedback control utilizing device as a spectrometer or monitor sensor for both self monitoring as well as control of the optical transmission line.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, the invention is a novel intelligent, all optical, high speed, single and multichannel, bulk acousto optic and integrated optic surface acoustic wave, adaptable, dynamic gain flattening filter and/or monitoring control loop system for fiber optic communication networks, useful for flattening or custom changing optical response across the optical wavelength band inside a fiber optic network transmission line caused by the different response characteristics of the lasers, fibers, detectors, dynamic add/drops, cascaded amplifiers, optical components, fiber optic .amplifiers and other components of the network shown in overview in Figure 1.

Figure 1 depicts the schematic drawing of our invention for an intelligent, all optical, high speed, bulk acousto optic, dynamic gain flattener. The input fiber optic light source 1 which may be either polarized or unpolarized light is coupled via a lens 2 into two cascaded acousto optic medium 3. The light interacts with the sound wave generated by the piezoelectric acoustic transducers 4 to create three or more light beams from each acousto-optic medium 3 : the zero order undeflected light beam and two deflected first order beams (+1 and -1 order) , and sometimes even higher order beams . The undeflected zero order beam is coupled back into the output optical fiber 5 via lens 2.

In Figure 1 single or multiple radio frequency .(RF) power is applied to the acoustic transducer 4 which generates sound waves and the each wave interacts, with the light beam to deflect our a portion of optical power within certain wavelength range to compensate for the different intensities of optical wavelength energies over the optical transmission band in the fiber network. By aidjusting the RF power of the individual RF frequencies it ^'is then possible to compensate for, the variation in amplitude either by an instantaneous feedback control loop arrangement or a remotely controlled arrangement thus creating a bulk acousto optic, real time, dynamic, adaptive gain flattening filter.

Figure 2 is an alternate configuration of Figure 1 with folded optical path. In Figure 2 the zero order beam is^' back reflected into another acousto optic device 3 by any means such as mirrors 6, prisms 6, reflective ■ . coating 6, or any reflector arrangement, etc. The undeflected zero order beam is coupled back into the output optical fiber 5 via lens 2.

In Figure 3 an array of piezoelectric transducers 4 on the multi channel, bulk acousto optic device 3 can be configured into a real time acousto optic, dynamic, gain flattening filter. In this case the input fibers 1 from transmission line can be coupled into the ganged device 3 to minimize size and power requirements , extend the number of channels, and cover broader optical spectrum range. The undeflected zero order beam is coupled back into the output optical fiber 5 via lens 2.

Figure 4 is an alternate configuration of Figure 3 where optical path is folded with prisms and coupled optical fibers. In this case input fiber 1 from transmission line can be coupled into the ganged device 3 to minimize size and power requirements. Similarly after the light passes through the multiple channels, bulk acousto optic gain flatteners . The undeflected zero order beam is then coupled into the output fiber 5 via lens 2.

In Figure 5, detector 8 and/or detectors 9 are placed at the +1 order and/or -1 order of deflected beams to monitor the deflected optical wavelength which contain information about the optical response in the transmission line from input fiber 1. Since RF energies are already coupled into the transducer 4 and now by monitoring the detector response at either 8 or 9 or both as a function of wavelength for example, a spectrometer or monitor sensor is created from the same bulk acousto optic device configuration. This information can be used to flatten or custom change the optical spectrum of zero order beam which is coupled into the output fiber 5.

Similarly, the bulk devices in Figure 6 and 7 coupled with detectors make them act as both gain flattener and/or custom response changers as well as self monitoring and self controlling devices, as they are optically coupled in and out of the fiber transmission line.

In Figure 8, in order to establish an automatic feedback control system to the acousto optic gain flattening device assembly 10, a spectrometer 11 or monitor may or may not be combined with the said gain flattening device assembly 10. In Figure 8, either the spectrometer 11 which operates over the optical band of the fiber transmission line is coupled in line via an optical splitter 13, for example, with a control loop assembly 12 to the adaptive gain flattener 10, or in Figure 9, the spectrometer 11 or a monitor is mounted at the end of the fiber haul 14 to monitor the optical response over the entire fiber transmission line.

In Figure 8 and Figure 9 the spectrometer 11 or monitor sensor can either be a mechanical grating type, an acousto optic tunable filter type, a diode CO CO ISO ro μ> μ> o π o Cπ o cπ o

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waveguide 31 and flips or rotates the polarization of the light by 90 deg. The amplitude of the light with the rotated polarization is a function of the amplitude of the acoustic wave with a corresponding frequency generated by the interdigital transducer 30. The output polarization element 27 has the same effective angle as the input polarization element 26, thus blocking the light with a 90 deg rotated polarization, and allowing through the remaining light which is then coupled to the output fiber 2. By selecting the appropriate amplitudes of the acoustic waves generated by the interdigital transducer 30, appropriate amounts of each corresponding wavelength along the optical transmission line in the waveguide 31 will be attenuated thus flattening or custom shaping the spectral response 'over the transmission band.

The integrated optic surface acoustic wave devices in Figure 10 and Figure 11 can also be configured into the feedback control loop configurations in Figure 8 and Figure 9.

Hence, in Figure 12 by supplying feedback from the control circuit 23 to the gain flattening or custom changing device assembly 10 and hence by changing the RF power and RF frequency to flatten or custom change the optical response in the transmission line, the same device 10 which is used as a gain flattener and/or custom response changer is now used as a self monitoring and self controlling device assembly 32.

Thus, there has been described a novel intelligent,^' all optical, high speed, single and multichannel, ^'bulk acousto optic and integrated optic surface acoustic wave, adaptable, dynamic gain flattening filter and/or monitoring control loop system for fiber optic communication networks, useful for flattening or custom changing optical response across the optical wavelength band inside a fiber optic network transmission line caused by the different response characteristics of the lasers, fibers, detectors, dynamic add/drops, cascaded amplifiers, optical components, fiber optic amplifiers and other components of- the network that has a number of .novel features,, and a manner of making and using the invention.

While a specific embodiment of the invention has been shown and described ^• in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles and that various modifications, alternate constructions, and equivalents will occur to those skilled in the art given the benefit of this disclosure. Thus, the invention is not limited to the specific embodiment described herein, but is defined by the appended claims.

Claims

CLAIMSWe claim:

1. An apparatus for dynamic optical spectrum control, comprising:

a bulk acousto-optic medium;

a piezoelectric transducer coupled to said acousto-optic medium, said piezoelectric transducer responsive to radio frequencies and thinned down to a desired thickness corresponding to operating acoustic frequencies corresponding to desired deflected wavelengths selected from the optical spectrum of an input optical signal;

an input fiber for receiving said input optical signal, said input fibers coupled to said acousto-optic medium;

an output fiber coupled to said acousto-optic medium;

means for generating amplitude and frequency adjustable radio frequency signals, which are received by said transducer;

means for controlling the frequencies and amplitudes of said radio frequency signals with programmable circuit boards or other equivalent electronic devices;

wherein acousto-optic interaction deflects a selected band of wavelengths from said input optical signal so that said selected band is extracted from the transmitted light, and any remaining (unselected) bands of wavelengths (the "zero-order beam") are coupled into the output fiber.

2. The apparatus of claim 1, wherein multiple transducers are attached to each acousto optic medium.

3. The apparatus of claim 1, wherein one frequency is received by each said transducer so that a single-frequency acoustic wave is generated in said acousto optic medium.

4. The apparatus of claim 1, wherein multiple frequencies are received by each said transducer and thus multiple-frequency acoustic waves are generated in the said acousto optic medium.

5. The apparatus of claim 1 wherein said means for receiving said input optical signal comprises a grin lens or a ball lens .

6. The apparatus of claim 1, further comprising additional bulk acousto- optic media and optical means for folding the optical path of the zero-order beam with optics .

7. The apparatus of claim 6 wherein said optical means comprise a mirror.

8. The apparatus of claim 6 wherein said optical means comprise a prism.

9. The apparatus of claim 6 wherein said optical means comprise an optical fiber.

10.' An apparatus for dynamic optical spectrum control including dynamic gain flattening, comprising: input fibers and output fibers;

means for coupling input optical signal from said input fiber into said acousto optic medium;

means for coupling the output optical signal from said acousto optic medium into said output fiber;

two cascaded bulk acousto optic media with attached piezoelectric transducers responsive to radio frequencies (RF) signals, thinned down to a desired thickness corresponding to the operating acoustic frequencies which relata to the desired deflected wavelengths out of the input optical spectrum;

means for attaching the said transducer to said acousto optic medium;

wherein the said means for spectrum control/chromatic equalizing/manipulating the transmitted spectrum, consists of a set of said acousto optic media with attached said transducers, where through acousto-optic interaction a portion of a selected bands of wavelength of the transmission spectrum is deflected out and the left over light, the undeflected 0-order beam is coupled back into the output fiber optic transmission line;

means for receiving RF signal by said transducers;

means for generating amplitude and frequency adjustable radio frequency signals, which are received by said transducers; means for controlling the frequencies and amplitudes of said RF signals, with programmable circuit boards or other equivalent electronic devices;

means for detecting the optical power of deflected optical beams out of the 0 order.

11. The apparatus of claim 10, comprising more than two acousto optic media.

12. The apparatus of claim 10, wherein one frequency signal is received by each said transducer.

13. The apparatus of claim 10, wherein multiple frequency signals are received by each said transducer.

14. The apparatus of claim 10, further comprising optical means for folding the optical path of the zero-order beam with optics.

15. The apparatus of claim 14 wherein said optical means comprise a mirror.

16. The apparatus of claim 14 wherein said optical means comprise a prism.

17. The apparatus of claim 14 wherein said optical means comprise an optical fiber.

18. An apparatus for dynamic optical spectrum control, comprising:

an integrated optic surface acoustic wave device utilizing a planar optical waveguide;

one or more interdigital transducers coupled to said planar optical waveguide, each of said ^' transducers responsive to radio frequencies and patterned to a desired shape corresponding to operating acoustic wave frequencies corresponding to desired deflected wavelengths selected from the optical spectrum of an input optical signal;

an input fiber for receiving said input optical signal, said input fiber coupled to said optical waveguide;

an output fiber coupled to said optical waveguide; means for generating amplitude and frequency adjustable radio frequency signals, which are received by said transducer;

means for controlling the frequencies and amplitude of said radio frequency signals with programmable electronic devices;

means for delivering the said radio frequency signals to said transducers, as by an impedance matching circuit;

wherein acousto-optic interaction deflects a selected band of wavelengths from said input optical signal so that said selected band is separated away from said input optical signal and any remaining (unselected) bands of wavelength (the "zero-order beam") are coupled into the output fiber.

19. The apparatus of claim 18, wherein one frequency is received by each of said transducers .

20. The apparatus of claim 18, wherein multiple frequencies are received by each said transducer.

21. An apparatus for dynamic optical spectrum control, comprising:

an integrated optic surface acoustic wave device ("waveguide") utilizing an optical mode conversion with one or more interdigital transducers, each of said transducers activated by one or multiple radio frequency driving signals, said radio frequency corresponding to desired deflected wavelengths selected from the optical spectrum of an input optical signal;

an input fiber for receiving said input optical signal, said input fiber coupled to said optical waveguide;

an output fiber coupled to said optical waveguide;

means for generating amplitude and frequency adjustable radio frequency signals, which are received by said transducer;

means for controlling the frequencies and amplitude of said radio frequency signals with programmable electronic devices;

impedance matching circuit means for delivering the said radio frequency signal to said transducers;

wherein acousto-optic interaction converts a selected band of wavelengths from fundamental mode of the said waveguide to higher mode and the higher modes are extracted away from the said fundamental mode and then the remaining fundamental mode is coupled into output fiber.

22. The apparatus of claim 21, wherein one frequency is received by each said transducer.

23. The apparatus of claim 21, wherein multiple frequencies are received by each said transducer.

24. An apparatus for Closed Loop Feedback Control utilizing a spectrometer or monitor sensor next to or at a distance to a said dynamic optical spectrum control including dynamic gain flattenning device comprising:

a said dynamic optical spectrum control including bulk acousto-optic media and integrated optic waveguide surface acoustic wave (planar or optical mode conversion waveguide) dynamic gain flattening device;

means for obtaining optical spectrum of processed optical signal (spectrometer or monitor sensor for example) ;

means for analyzing said obtained optical spectrum (software stored in memory, for example) ;

means (RF driver board for example) for modifying the amplitudes and frequencies that driving the said gain flattening device ( via transducers) .