Optical: systems and elements – Optical frequency converter
Reexamination Certificate
2003-02-06
2004-09-21
Lee, John D. (Department: 2874)
Optical: systems and elements
Optical frequency converter
C359S332000
Reexamination Certificate
active
06795233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a cross-gain modulation type optical wavelength converter, and more particularly to a cross-gain modulation type optical wavelength converter which is capable of preventing an extinction ratio from lowering and allowing an input dynamic range to widen.
2. Description of the Prior Art
As the amount of transmitted information has rapidly increased recently, demands on transmission capacities of communication networks have increased and the capacities of transmission systems tend to grow increasingly large due to the increasing demands. In this circumstance of various technologies of increasing a transmission velocity that have been proposed up to now, a Wavelength Division Multiplexing (WDM) transmission technology has been most actively studied in that communication can be carried out over a wide bandwidth provided by optical fiber by utilizing the optical wavelengths of various channels. An optical wavelength converter is an important element of a communication network using a WDM transmission apparatus, along with a semiconductor optical amplifier (SOA). Such an optical wavelength converter generally converts the wavelength of a signal using the cross-gain modulation (XGM), cross-phase modulation (XPM) or photo-electric-photo conversion of an optical signal and a probe light.
In general, wavelength converters are apparatuses that convert wavelengths of transmission signals without regard to transmission velocities and transmission methods. The wavelength converters serve to reduce wavelength blocking caused by wavelength contention in WDM communication networks and increase the flexibility and capacity of the networks for fixed wavelengths by reusing useful wavelengths. Additionally, the wavelength converters serve to allow networks to be managed while being distributed, and additionally serve to allow protection switching to be easily performed.
There are various embodiments of the optical wavelength converters, which may be classified into three types. The first is an XGM type using the XGM characteristics of an SOA. The second is an XPM type using the XPM characteristics of an SOA. The third is a Four Wave Mixing (FWM) type, which generates optical signals having new wavelengths and wavelength-convert the optical signals through FWM. The XGM type is most commonly used and simplest to implement.
Such a conventional XGM type optical wavelength converter is shown in FIG.
1
. Referring to
FIG. 1
, a pump light
102
is an intensity-modulated input optical signal having a wavelength of &lgr;
s
. A probe light
106
is a Continuous Wave (CW) light having a wavelength &lgr;
c
, which is outputted from a CW light source
104
. The pump light
102
and probe light
106
are simultaneously inputted to an SOA
101
. The gain of the SOA
101
is modulated by the pump light
102
. The probe light
106
is influenced by the gain modulation Of the SOA
101
, so the probe light
106
is intensity-modulated in the same manner as the pump light
102
. Since the SOA
101
outputs the pump light
102
and the wavelength-converted probe light at its output terminal, a Band-Pass Filter (BPF)
107
is employed to pass therethrough only a wavelength-converted light
103
.
The conventional XGM type optical wavelength converter is problematic in that the extinction ratio of a wavelength-converted signal outputted from the SOA at the time of wavelength conversion is lowered due to the gain characteristics of the SOA, a bit stream is reversed and an input dynamic range is narrow.
Meanwhile, a method of reducing the gain recovery time of an SOA so as to wavelength-shift optical signals of a high bit rate in a wavelength-shifter using XGM characteristics in the SOA, is disclosed in U.S. Pat. No. 5,450,229 entitled “Optical wavelength-shifter with reduced gain recovery time” and issued to Jay M. Wiesenfeld. This patent provides a method of wavelength-shifting optical signals of a high bit rate by using characteristics of reducing gain recovery time of an amplifier by the intensity of a CW light and, thus, reducing rise time at the time of XGM of the CW light in a general optical wavelength-shifter, thereby wavelength-shifting the optical signals having a bit rate of 10 Gb/s or higher using the gain saturation characteristics of a SOA.
Furthermore, in “Technique for Suppression of Pattern Dependence in a Semiconductor Optical Amplifier Wavelength converter”, IEEE Photonics Technology Letters, Vol. 9, No. 12, pp. 1583-1585, December 1997, a method of reducing pattern dependence in a wavelength converter using XGM characteristics in an SOA was proposed by D. Mahgereft eh et al., in 1997. Generally, wavelength conversion using XGM characteristics in an SOA is a reaction dependent on the pattern of the SOA, and has a limitation in a bit rate of data to be converted. Accordingly, in this method, the pattern dependence is solved by converting phase modulation to amplitude modulation at the time of data transition using a fiber grating filter.
In the conventional XGM type optical wavelength converter, the lowering of the extinction ratio of a wavelength-converted signal outputted from the SOA due to the gain characteristics of the SOA at the time of wavelength conversion and the narrowing of the input dynamic range cannot be fundamentally overcome.
SUMMARY OF THE INVENTION
The present invention provides an optical wavelength converter, which is provided with a high extinction ratio and a wide dynamic input range by allowing a probe light to be primarily influenced by cross-gain modulation of the first SOA caused by the first pump light and to be secondarily influence by cross-gain modulation of the second SOA caused by the second pump light, and by detecting the intensity of an optical signal inputted to the optical wavelength converter and automatically controlling the intensity of the probe light on the basis of the detected intensity of the input optical signal, respectively.
The foregoing and other objects of the present invention are achieved by providing a cross-gain modulation type optical wavelength converter converting the optical wavelength of a probe light outputted from a continuous wave light source by using an intensity-modulated pump light, comprising: an optical division unit for dividing the intensity-modulated pump light into first pump light and second pump light on a basis of a predetermined light intensity ratio; a first control unit for detecting an intensity of the first pump light and controlling an intensity of the probe light outputted from the continuous wave light source in proportion to the detected intensity of the first pump light; a first semiconductor optical amplifier for performing a cross-gain modulation by using the first pump light and first converting the wavelength of the probe light outputted from the continuous wave light source on a basis of the cross-gain modulation; a second control unit for controlling an intensity of the first wavelength-converted probe light outputted from the first semiconductor optical amplifier in proportion to an intensity of the second pump light; and a second semiconductor optical amplifier for performing a cross-gain modulation by using the second pump light and second converting the wavelength of the first wavelength-converted probe light intensity-controlled by the second control unit on a basis of the cross-gain modulation.
It is preferable that the optical wavelength converter further comprises an optical phase control unit for controlling a phase of the second pump light so as to be in phase with the first pump light.
Additionally, it is preferable that the first control unit comprises a first optical extraction means for extracting some of the first pump light, a first optical detection means for detecting the extracted first pump light and converting the extracted first pump light into an electrical signal, and a light source drive control means for controlling the continuous wave light source using the electrical signal and a preset e
Bang Joon Hak
Ko Je Soo
Blakely & Sokoloff, Taylor & Zafman
Electronics & Telecommunications Research Institute
Lee John D.
LandOfFree
Cross-gain modulation type optical wavelength converter... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cross-gain modulation type optical wavelength converter..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cross-gain modulation type optical wavelength converter... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3189852