Optics: measuring and testing – By light interference – Using fiber or waveguide interferometer
Reexamination Certificate
2002-09-09
2004-08-24
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Using fiber or waveguide interferometer
Reexamination Certificate
active
06781698
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for rapidly evaluating the performance of optical components. In particular, the present method allows for a rapid characterization of the performance of optical components, such as Bragg gratings, which allows enhanced quality control and monitoring.
BACKGROUND
Optical components are devices that handle or process an optical signal. An important type of optical components are fiber Bragg gratings. Bragg gratings are patterns of refractive index perturbations. Long-length Bragg gratings, generally gratings longer than a quarter of a meter, are especially useful as dispersion compensation devices.
Dispersion compensation fiber Bragg gratings (DCFBGs) are becoming widely incorporated into optical telecommunication systems. Fabrication errors in chirped gratings may create unwanted variations in the optical group delay across the bandwidth of a fiber Bragg grating (FBG) dispersion compensation module and thus inaccuracies in its dispersion correction. These variations in the group delay are commonly referred to as delay ripple.
Relating the delay ripple characteristics of a DCFBG to its performance in a given optical system has been challenging, and most researchers will have confidence in a given DCFBG only after testing it fully in their systems. The performance of an optical component may be measured in several ways. Two important values for each optical component are generally the eye opening power penalty (EOPP) and bit error rate (BER). Eye opening power penalty is defined as the amount of the signal intensity increase to maintain the same BER. Bit error ratio (BER) is defined as the ratio between the number of errors detected by the receiver and the total number of bits transmitted.
Actual measurements of BER or EOPP are time-consuming. A typical actual measurement for a DCFBG entails conducting BER or EOPP measurements across the full bandwidth of the device with a spectral resolution of a few picometers. Fine-resolution BER tests across a chirped FBG with a bandwidth of a few nanometers can take tens of hours, and measurements across full-band devices (~30 nm) can require over 100 hours of evaluation time, making mass-production or testing of these devices impractical. A method is needed to identify quickly and accurately a defective DCFBG to increase manufacturing volumes and thus lower production costs. Such a method would be even more desirable if it also could be used to test the performance of discrete devices, such as equipment received from vendors, stored in inventory, or placed in the field.
SUMMARY
The present invention relates to a modulation phase shift (MPS) simulation method based on transfer function (TF) and modulation transfer function (MTF) of an optical component, such as a DCFBG, that allows one to quickly and accurately obtain the component's performance.
A method for screening the quality of an optical component in accordance with the present invention included the step of simulating the performance of the optical component. The step of simulating comprises the steps of measuring the optical phase &phgr; of the optical component. The step of measuring comprises indirectly measuring the optical phase &phgr; of the optical component using a scanning laser having a scanning step size &Dgr;&ohgr; and a modulation frequency &ohgr;
m
such that &Dgr;&ohgr;/&ohgr;
m
≦2.
The light throughput R of the optical component is measured. A transfer function H as a function of optical frequency &ohgr; is constructed where H(&ohgr;)=R(&ohgr;)exp[j&phgr;(&ohgr;)]. The performance is then simulated using the measured value of the optical phase and the light throughput into the transfer function.
The optical component may be an optical Bragg grating or a dispersion compensation optical grating. In a particular embodiment, the grating has a bandwidth greater than 1 nanometer. In a particular embodiment, &Dgr;&ohgr;/&ohgr;
m
=2.
The step of measuring may comprises using an interferometer.
A method to simulate the performance (power penalty and bit error ratio) of an optical component, comprising the steps of:
measuring the phase &phgr; of the optical component;
measuring the light throughput (reflectivity R or transmissivity) of the optical component;
constructing a transfer function H as a function of frequency or wavelength where
H
(&ohgr;)=
R
(&ohgr;)exp[
j
&phgr;(&ohgr;)]
simulating the performance using the transfer function.
Both TF and MTF may be constructed with the method of the present invention. For a 30-nm band DCFBG, the simulation takes a few minutes, compared to approximately 100 hours for comparable BER or EOPP measurement to obtain similar information. For a 4 nm bandwidth DCFBG, practice of a method according to the present invention takes less than 1 minute and matches well the experimental data.
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Brennan, III James F.
Fan Xudong
Matthews Michael R.
Porque Jerome C.
Sinha Pranay G.
3M Innovative Properties Company
Lyons Michael A.
Rosenblatt Gregg H.
Turner Samuel A.
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