JP3737402B2 - Optical signal regeneration inverter using a mode-locked integrated semiconductor laser. - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical signal reproducing inverter using a mode-locked integrated semiconductor laser.
[0002]
[Prior art]
Conventionally, the references disclosed in such fields are disclosed below.
[0003]
(1) Wolfson, D .; , Kloch, A .; Fjelde, T .; Janz, C .; Dagens, B .; , And Renaud, M .; : '40 -Gb / sall-optical wave length conversion, regeneration and demultiplexing in an SOA-based all-active Mach-Zehnder interferometer ', IEEE Phot. Technol. Lett. , 2000, 12, (3), pp. 332-334
(2) Kurita, H .; , Hashimoto, Y .; Ogura, I .; Yamada, H .; , And Yokoyama, H .; : 'All-optical 3R regeneration based on optical clock recovery with mode-locked LDs', Proc. ECOC'99, 1999, Postdeadline Paper PD3-6, pp. 56-57.
(3) Arahira, S .; , Matsui, Y .; , Kunii, T .; Oshiba, S .; , And Ogawa, Y .; : 'Transform-limited optical short-pulse generation at high repetition rate over 40 GHz from a monolithic passive mode E-locked EDR'. Technol. Lett. 1993, vol. 5, pp. 1362-1365.
(4) Weich, K .; Horer, J .; Patzak, E .; , As, D .; J. et al. , Eggmann R., et al. , And Mohrle, M .; : 'Injection locked laser as wavelength converter and optical regenerator up to 10 Gbit / s', Proc. ECOC '94, 1994, pp. 643-646.
(5) Parallari, P .; , And Marazzi, L .; : 'SOA based all-optical threshold' Proc. CLEO 2000, pp. 309-310.
(6) Maeda, Y .; : 'All inverted operational derived from negative non-feedback systems', Electron. Lett. , 2000, vol. 36, pp. 1138-1139.
(7) Fukushima, T .; , And Sakamoto, T .; : 'Optical signal inverter using injection locking of coupled semiconductor lasers', Jpn. J. et al. Appl. Phys. 1997, vol. 36, pp. L280-L282.
In the next generation optical network, the search for a high-performance and compact all-optical signal regeneration device is very interesting.
[0004]
Among such all-optical signal regeneration devices, the most likely candidates at the moment in terms of performance are:
(A) There is a method of realizing optical regeneration by a configuration using a Mach-Zehnder interference system of a semiconductor amplifier (SOA). For example, in a 40 GHz / s RZ (Return to Zero) signal, an improvement in the signal-to-noise ratio of 20 dB or more has been reported.
[0005]
(B) As another promising and simple method, there is a method using light injection to a semiconductor mode-locked laser (MLLD). For example, 3R (regenerating, reshaping, retiming) realization of a 20 Gb / s pulse train using this method has been reported.
[0006]
[Problems to be solved by the invention]
However, the conventional all-optical signal reproducing device described above has the following problems.
[0007]
(A) In the all-optical signal reproducing device of (a) described above, this configuration requires some SOA and a CW (continuous wave) light source different from the signal light, so that the system becomes complicated. There is.
[0008]
(B) Since the all-optical signal reproducing device of (b) described above uses a mode lock of a fixed frequency, it is limited to use at this bit rate, and has potential in terms of variability of the used frequency. There is a problem.
[0009]
In view of the above circumstances, an object of the present invention is to provide an optical signal reproduction inverter using a mode-locked integrated semiconductor laser having a digital characteristic that is simpler and has higher performance and flexibility in use frequency. .
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] In an optical signal regeneration inverter using a mode-locked integrated semiconductor laser, an optical circulator that inputs modulated light, and the modulated light is connected to the optical circulator and the modulated light is transmitted through the optical circulator. A distributed Bragg reflector type laser that is input and receives an input signal light wavelength λ _in that is a wavelength of modulated light that is slightly shifted from one of the two oscillation wavelengths λ _1. A two-mode oscillation semiconductor mode-locked laser having a small band and two limited two-oscillation wavelengths and output light from the two-mode oscillation semiconductor mode-locked laser are input via the optical circulator, and the two oscillation wavelengths A band-pass filter that extracts only the other wavelength λ _2, and has a steep switching characteristic And
[0011]
[2] In the optical signal regeneration inverter using the mode-locked integrated semiconductor laser as described in [1] above, the modulated light is obtained by modulating laser light from a continuous wave laser source with a modulator. And
[0012]
[3] In the optical signal reproducing inverter using the mode-locked integrated semiconductor laser described in [1] or [2] , one of the two oscillation wavelengths λ ₁ is 1563.67 nm, and the two oscillation wavelengths The other wavelength λ ₂ is 1563.97 nm .
[0013]
[4] In the optical signal reproduction inverter using the mode-locked integrated semiconductor laser according to [1], [2] or [3], the gain current applied to the two-mode oscillation semiconductor mode-locked laser is 127 mA, supersaturated The applied voltage to the absorption band is -1.0 V, and the mode interval is about 36 GHz.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0015]
FIG. 1 is a block diagram of an optical signal regeneration inverter using a mode-locked integrated semiconductor laser according to an embodiment of the present invention.
[0016]
In this figure, 1 is a continuous wave (CW) laser (LD) and 2 is an MZM (Mach Zehnder Modulator ) , which divides the optical path into two and applies a voltage to one of the optical paths. Thus, the modulator changes the optical path length and changes the phase of the light. The material, a Li NbO ₃ (referred to for short LN), it changes the optical path length when a voltage is applied to the electro-optic crystal.
[0017]
3 is an optical circulator, 4 is a two-mode oscillation semiconductor mode-locked laser (two-mode oscillation MLLD), 5 is an optical coupler, 6 is an optical bandpass filter (BPF), 7 is a photodetector (PD), and 8 is An optical spectrum analyzer (OSA), 9 is a voltage source (DC power supply), 10 is a current source, and 11 to 17 are optical fibers.
[0018]
In this figure, except for passive elements such as the optical circulator 3 and the optical bandpass filter (BPF) 6, the inverter operation is realized with a very simple configuration of only the two-mode oscillation MLLD4. The structure is simpler than that of an optical signal reproducing element.
[0019]
FIG. 2 is a diagram illustrating an oscillation mode of a two-mode oscillation semiconductor mode-locked laser according to an embodiment of the present invention, which is observed by an optical spectrum analyzer (OSA) 8. The horizontal axis indicates the wavelength (nm) and the vertical axis indicates the input signal light wavelength indicating the optical power (20 μW / scale).
[0020]
2 (a) is the optical input power P _in is 0MyuW, FIG. 2 (b) its optical input power P _in is 3 W, FIG. 2 (c) its optical input power P _in is 5 W, FIG. 2 (d) its optical input power P _in is 5.5MyuW, FIG 2 (e) has its optical input power P _in 7MyuW, FIG 2 (f) is the optical input power P _in is shown a case of 15μW each.
[0021]
The two-mode oscillation MLLD 4 in FIG. 1 is a distributed Bragg reflector (DBR) type laser. Since the reflection band of the MLLD 4 used in the present invention is small, the oscillation mode is 2 as shown in FIG. Limited to one. That is, M1 has an oscillation wavelength of 1563.67 nm, and M2 has an oscillation wavelength of 1563.97 nm. These two modes M1 and M2 oscillate at an asymmetric power ratio. During operation, the applied gain current to the two-mode oscillation MLLD4 is 127 mA, and the applied voltage to the saturable absorption band is -1.0V. The mode interval is approximately 36 GHz. The input signal light wavelength λ _in is set to 1563.71 nm slightly shifted from λ ₁ . M2 is output.
[0022]
Further, only the output signal [output (λ ₂ ): mode M2] described above is extracted and obtained by the optical bandpass filter (BPF) 6 .
[0023]
The detailed description of the MLLD (Mode Locked DBR Laser Diode) itself is described in the above-mentioned prior document (3) IEEE Photon. Technol. Lett. 1993, vol. 5, pp. 1362-1365. However, in the present invention, the MLLD is applied for two-mode oscillation.
[0024]
FIG. 3 is a characteristic diagram of optical output power P _out (μW) [upper] and wavelength (0.05 nm / scale) [lower] with respect to optical input power P _in (μW).
[0025]
The inset shows an output eye pattern when a 155.52 Mb / s data signal is input. Very steep switching characteristics and dynamic inverter characteristics near the threshold are clearly shown.
[0026]
Moreover, (a)-(f) of FIG. 3 has shown the measured output light spectrum. The numerical values are values in consideration of the connection loss between the optical circulator 3 and the optical fiber 13 and the two-mode oscillation MLLD 4. When the optical input power P _in is 5 μW or less, the mode λ _{in of the} input light is only slightly observed. In a narrow range of optical input power P _in is 5～7MyuW, power ratio rapidly lambda _in mode and M2 mode is changed. Single-mode oscillation is realized in lambda _in mode in the range optical input power P _in is equal to or higher than 7MyuW.
[0027]
When these states are plotted with the horizontal axis representing the optical input power P _in and the vertical axis representing the optical output power P _out , (a) to (c) and (e) shown in the upper part of FIG. It is confirmed that very steep switching is realized along with the flatness in (f).
[0028]
Such a characteristic is very interesting as a suggestion of a function for realizing waveform reproduction. The switching threshold power is the lowest value reported so far, and is a value at which high sensitivity can be expected. Further, the output signal light power P _out is approximately 70MyuW, since it is a 10 times the value of the input signal light power, if subtracting the connection loss of the circulator 3 and the optical fiber 13 and the secondary mode oscillation MLLD4 also the optical signal power regeneration function as thought is expected.
[0029]
Here, an attempt is made to explain this characteristic using the following model.
[0030]
Reasons flatness in (a) ~ (c) in FIG. 3, mode competition between the M1 and lambda _in is the main, it is believed to be due not to affect the power of M2. The abrupt switching in the (c) to (e) regions begins at the end of mode competition between M1 and λ _in and is considered to be due to the effects of injection locking and cross-gain modulation (XGM). That is, the end of mode competition means realizing injection locking of M1 with respect to λ _in , and at the same time, the oscillation power at λ _in increases rapidly. Then, the mutual gain modulation (XGM) leads to a rapid decrease in the gain at M2, and the oscillation power in the M2 mode is considered to be suppressed to almost zero.
[0031]
Furthermore, the dynamic characteristics were clarified. That is, the dynamic characteristics in a 155.52 Mb / s, NRZ (Non Return to Zero) signal were confirmed. The eye pattern is shown in the inset of FIG. According to the inset of FIG. 3, it is confirmed that the eye is open, and the operation at this bit rate is confirmed.
[0032]
In addition, the operating frequency band of the inverter is suppressed to 1.8 GHz, which is considered to be limited to this value because it substantially matches the relaxation oscillation frequency of the laser. It can be improved by using a high laser.
[0033]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0034]
【The invention's effect】
As described above in detail, according to the present invention, optical signal regeneration using a mode-locked integrated semiconductor laser having steep switching characteristics with a more compact configuration utilizing light injection to the two-mode oscillation MLLD. An inverter can be obtained.
[0035]
That is, since the input / output static characteristics have a steep switching characteristic comparable to that of an electronic circuit inverter, a waveform regenerating function can be expected. Further, the gain for the input signal is also confirmed, and a signal power regeneration function can be expected. Furthermore, since there is no restriction on the operating frequency in this operation format, it can be used in the NRZ signal.
[Brief description of the drawings]
FIG. 1 is a block diagram of an optical signal regeneration inverter using a mode-locked integrated semiconductor laser according to an embodiment of the present invention.
FIG. 2 is a diagram showing an oscillation mode of a two-mode oscillation semiconductor mode-locked laser showing an embodiment of the present invention.
FIG. 3 is a diagram showing measured optical input / output power characteristics and an output eye pattern when a 155.52 Mb / s data signal is input according to an embodiment of the present invention, and the optical output power with respect to the optical input power P _in (μW); P _out (μW) [top] and wavelength (0.05 nm / scale) [bottom] are shown.
[Explanation of symbols]
1 Continuous wave (CW) laser (LD)
2 MZM (Mach-Zehnder interferometric modulator)
3 Optical circulator 4 Two-mode oscillation semiconductor mode-locked laser (two-mode oscillation MLLD)
5 Optical coupler 6 Optical band pass filter (BPF)
7 Photodetector (PD)
8 Optical Spectrum Analyzer (OSA)
9 Voltage source (DC power supply)
10 Current source 11-17 Optical fiber

Claims (4)

(A) an optical circulator for inputting modulated light;
(B) Connected to the optical circulator, the modulated light is input through the optical circulator, and the modulated light wavelength is slightly shifted from _one wavelength λ ₁ of the two oscillation wavelengths. A two-mode oscillation semiconductor mode-locked laser that is a distributed Bragg reflector type laser to which a certain input signal light wavelength λ _in is input, has a small reflection band , and two limited two oscillation wavelengths;
(C) a band-pass filter that inputs output light from the two-mode oscillation semiconductor mode-locked laser through the optical circulator and extracts only the other wavelength λ ₂ of the two oscillation wavelengths ; An optical signal regeneration inverter using a mode-locked integrated semiconductor laser, characterized by having steep switching characteristics.   2. An optical signal regeneration inverter using a mode-locked integrated semiconductor laser according to claim 1, wherein the modulated light is obtained by modulating laser light from a continuous wave laser source with a modulator. An optical signal regeneration inverter using an integrated semiconductor laser. 3. The optical signal regeneration inverter using the mode-locked integrated semiconductor laser according to claim 1 or 2, wherein one of the two oscillation wavelengths λ ₁ is 1563.67 nm and the other of the two oscillation wavelengths is λ. An optical signal regeneration inverter using a mode-locked integrated semiconductor laser, wherein ₂ is 1563.97 nm.   4. The optical signal regeneration inverter using the mode-locked integrated semiconductor laser according to claim 1, 2, or 3, wherein the applied gain current to the two-mode oscillation semiconductor mode-locked laser is 127 mA, and the applied voltage to the supersaturated absorption band is -1. An optical signal regeneration inverter using a mode-locked integrated semiconductor laser characterized in that the mode interval is about 36 GHz at 0.0 V.

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