Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
2001-03-30
2003-02-25
Hellner, Mark (Department: 3663)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S337000
Reexamination Certificate
active
06525873
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical amplifiers and more specifically to automatic gain and output power control of Optical Amplifiers.
BACKGROUND
In recent years optical amplifier modules have undergone considerable transformation. Increased demand for more data transfer resulted in development of wavelength division multiplexing (WDM) technology, which allows more data to be transmitted over one fiber by increased channel count (i.e., a larger number of narrower wavelength ranges within the same predetermined wavelength window). This WDM technology suffers from unwanted effects, such as a variation in output power when the input signal power is constant (for example, due to aging of the amplifier or due to stresses in the amplifier), and cross talk between different channels, for example, when the input signal is modulated at a low frequency. The low frequency is a frequency of up to 10 kHz. This low frequency modulation can be present, for example, due to the addition or dropping of some to the channels, or due to sudden loss of signal at certain wavelengths. These unwanted effects have a negative influence on the power transients (i.e., fluctuations of output optical signal power) of surviving channels, which results in a poor performance of the signal transmission, expressed in an increased bit error rate (BER).
In order to minimize the unwanted output signal power fluctuation and the power transients due to the cross talk or other causes (such as fiber damage, adding or dropping of channels), it is common to introduce a mechanism for controlling either the output signal power or the gain of the optical fiber amplifier. Gain is the ratio of the optical signal output power to the optical signal input power.
There are two known approaches for controlling output signal power or the gain of the optical fiber amplifier. The first approach, known as the electronic feedback/feed-forward approach, utilizes electronic circuitry to control power transients caused by the crosstalk produced in the optical fiber amplifier. More specifically, amplifier gain or power is controlled by analog tuning of the electronic components, for example by changes resistor's or capacitor's values. This approach allows the user, such as a communication company, to minimize power transients in any given optical amplifier by controlling either the amplifier gain or the amplifier output power, but not both. This approach also limits accuracy of gain control when signal power is small. Finally, this approach does not compensate for amplifier noise, such as ASE (amplified spontaneous emission).
The second approach, known as the optical feedback control approach, utilizes only optical components to control power transients of the optical fiber amplifier. This approach is even less flexible than the all-electronic approach described above, because any change in power or gain control requirements requires the change in optical components.
SUMMARY OF THE INVENTION
The optical fiber amplifier of the present invention is describerd in the appended claims.
Embodiments of the present invention can provide an optical amplifier and a control technique that overcomes the difficulties associated with known optical amplifiers. It is an advantage of this optical amplifier that it has a flexible controller that provides a choice of different control parameters. It is also an advantage of this optical amplifier that it automatically suppresses power transients by fast control of the amplifier gain or the total output power. It is further an advantage of this optical amplifier that the controller minimizes the influence of amplifier ASE noise.
For a more complete understanding of the invention, its objects and advantages refer to the following specification and to the accompanying drawings. Additional features and advantages of the invention are set forth in the detailed description, which follows.
It should be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.
REFERENCES:
patent: 5909305 (1999-06-01), Kinoshita
patent: 5940209 (1999-08-01), Nguyen
“Dynamic Gain Compensation in Saturated Erbium-Doped Fiber Amplifiers”, E. Desurvire et al., IEEE Photonics Technology Letters, vol. 3, No. 5, May 1991, 453-455.
“Dynamic Compensation of Transient Gain Saturation in Erbium-Doped Fiber Amplifiers by Pump Feedback Control” K. Motoshima et al., IEEE Photonics Technology Letters, vol. 5, No. 12, Dec. 1993, 1423-1426.
“Dynamic Gain and Output Power Control in a Gain-Flattened Erbium-Doped Fiber Amplifier”, Seo Yeon Park et al., IEEE Photonics Technology Letters, vol. 10, No. 6, Jun. 1998, p. 787-789.
“Dynamic Gain Control by Maximum Signal Power Channel in Optical Linear Repeaters for WDM Photonic Transport Networks” H. Suzuki et al., IEEE Photonics Technology Letters, vol. 10, No. 5, May 1998, 734-736.
“An Output Power Stabilized Erbium-Doped Fiber Amplifier with Automatic Gain Control” Nobuaki Takahashi et al., IEEE Journal of Selected Topics in Quantum Electronics, vol. 3, No. 4, Aug. 1997, 1019-1026.
“Fast Gain Control in an Erbium-Doped Fiber Amplifier” A.K. Srivastava et al., Bell Laboratories, Lucent Technologies, Crawford Hill Laboratory, PDP 4-2-PDP 4-5.
Gerrish Kevin S.
Lelic Muhidin
Corning Incorporated
Hellner Mark
Short Svetlana Z.
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