Patent Application
20100322624
1. Field of the Invention
The present invention generally relates to a bidirectional transmission network apparatus based on a tunable rare-earth-doped fiber laser, and, more particularly, to a passive optical network structure based on a Fabry-Pérot laser (or a vertical-cavity surface-emitting laser) injection-locked by the tunable rare-earth doped-fiber laser capable of being used as a downstream laser source at the central office (CO) of an optical fiber network and as a wavelength-selecting injection source for the upstream lasers at the subscriber site.
2. Description of the Prior Art
The demand in network capacity is increased due to intensive Internet usage, especially, through the wavelength-division multiplexing (WDM) access networks providing fiber-to-the-home (FTTH) triple-play service integrating audio, data and video signals. Therefore, each optical network unit (ONU) at the subscriber site requires a laser with a respective wavelength, which is capable of modulating uploaded data. This makes the passive optical network (PON) relatively expensive in the WDM system.
Conventionally, the light-emitting diode and the reflective semiconductor optical amplifier are used as light sources of optical network units (ONU's) at the subscriber site, which however leads to higher cost and requires complicated packaging. Recently, the injection-locked Fabry-Pérot (FP) laser is used as a light source of optical network units (ONU's) at the subscriber site because the Fabry-Pérot (FP) laser is less costly and requires simplified packaging. At the central office (CO) of an optical fiber network, the distributed feedback laser (DFB) and the amplified spontaneous emission (ASE) light source are used as light sources to be fed through an arrayed waveguide grating (AWG) into the FP laser. However, the former is problematic that the light source is temperature-sensitive and relatively costly, and the latter is disadvantageous that the arrayed waveguide grating requires precise temperature control.
Therefore, there is need in providing a tunable rare-earth doped-fiber laser capable of being used as a high-quality, adjustable and low-cost laser source at the central office (CO) and as a wavelength-selecting injection source for the upstream lasers at the subscriber site.
It is one object of the present invention to provide a bidirectional transmission network apparatus based on a tunable rare-earth-doped fiber laser injection-locked by a tunable laser wavelength to achieve bidirectional data transmission. The fiber laser not only generates downstream data traffic but also serves as the wavelength-selecting injection light source at the subscriber site for upstream signals. The tunable rare-earth-doped-fiber laser is useful in applications such as fiber-to-the-home (FTTH), wavelength-division multiplexing (WDM) access networks and passive optical networks (PONs).
In order to achieve the foregoing object, the present invention provides a bidirectional transmission network apparatus based on a tunable rare-earth-doped fiber laser, the bidirectional transmission network apparatus comprising: an office center (CO) module, comprising the tunable rare-earth-doped fiber laser; a remote node (RN) module, comprising an optical de-multiplexer and an optical multiplexer, each coupled to the office center module through a single-mode fiber; an optical network unit (ONU) module, comprising a semiconductor laser injection-locked by the tunable rare-earth-doped fiber laser.
In order to achieve the foregoing object, the present invention further provides a tunable rare-earth-doped-fiber laser, comprising: a pump laser diode, capable of providing pumping power; a wavelength-division multiplexer, coupled to the pump laser diode; a rare-earth-doped fiber, coupled to the wavelength-division multiplexer, so that the pump laser diode provides the rare-earth-doped fiber with the pumping power through the wavelength-division multiplexer to generate a wide-band amplified spontaneous emission (ASE) light; an optical tunable filter, coupled to the rare-earth-doped fiber to filter the wide-band amplified spontaneous emission light to generate a laser light with a determined wavelength, wherein the optical tunable filter is adjustable to determine the wavelength; a first optical circulator, coupled to the optical tunable filter to confine the propagation direction of the laser light; an optical polarization controller, coupled to the first optical circulator to control the polarization of the laser light; a semiconductor optical amplifier, coupled to the optical polarization controller to suppress noise from the laser light; an optical coupler, coupled to the semiconductor optical amplifier to split and couple out the laser light; and a second optical circulator, coupled to the optical coupler to confine the propagation direction of the laser light.
Thereby, the tunable rare-earth-doped fiber laser of the present invention does not only generate downstream data traffic but also serve as the wavelength-selecting injection light source at the subscriber site for upstream signals.
The objects, spirits and advantages of the preferred embodiment of the present invention will be readily understood by the accompanying drawings and detailed descriptions, wherein:
The present invention can be exemplified by the preferred embodiments as described hereinafter.
Please refer to
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Since the tunable rare-earth-doped-fiber laser 1 of the present invention is configured as a ring, it is used for both the high-speed downstream data from the center office and the upstream data from the subscriber site. Therefore, the split and coupled laser light from the optical coupler 9 is suitable for use as a laser source in optical fiber networks, WDM access networks or passive optical networks. Meanwhile, the split and coupled laser light from the optical coupler 9 is suitable for use as a laser source for wavelength conversion or to be injection-locked with a Fabry-Pérot laser or a vertical cavity surface-emitting laser (VCSEL) so that the signal from the wavelength conversion device, the Fabry-Pérot laser or the vertical cavity surface-emitting laser can be modulated to generate upstream data traffic to the center office. Since the wavelength of the tunable fiber laser is tunable, it can be used in networks with dynamic wavelength. By tuning the optical tunable filter 5, the wavelength of the laser can be determined. The optical polarization controller 7 is adjustable so that the power of the laser light is independent of the wavelength. The wavelength of the tunable rare-earth-doped-fiber laser is in the C-band or the L-band, while the Fabry-Pérot laser and the vertical cavity surface-emitting laser source also work in the C-band or the L-band.
In the present invention, the laser light from the tunable rare-earth-doped-fiber laser 1 passes through the optical polarization controller 12 and is then modulated by an electro-optic modulator 13 with a 10-Gb/s signal from a 10-Gb/s signal generator 14. After the modulated laser light is amplified by an rare-earth-doped fiber amplifier 15, it passes through a 10-km single-mode fiber 20 and is de-multiplexed by an optical de-multiplexer 21 before it is received by a 10-Gb/s signal receiver 17 of an optical network unit (ONU) at the subscriber site. Meanwhile, the laser light is split by an optical coupler 16 into two optical paths. One is coupled to the 10-Gb/s signal receiver 17 for downstream data, while the other is coupled to an optical circulator 22, which is fed with a Fabry-Pérot laser 18 (or a vertical cavity surface-emitting laser) of an optical network unit (ONU) at the subscriber site for wavelength locking so that the Fabry-Pérot laser 18 (or the vertical cavity surface-emitting laser) is capable of modulating a 1.25-Gb/s signal from a 1.25-Gb/s signal generator 19 at a high speed. The optical circulator 22 is also coupled to an optical multiplexer 23 for upstream data through a 10-km single-mode fiber 20 back to a 1.25-Gb/s signal receiver 24 at the center office.
The downstream laser at the center office is coupled to different optical network units (ONUs) at the subscriber site through the optical de-multiplexer 21 at the remote node (RN). The optical circulator 22 is used to determine the upstream optical path. The upstream laser at the subscriber site is coupled to the center office through the multiplexer 23 at the remote node (RN).
In order to realize the advantages of the present invention, please refer to
Therefore, in the present invention, the tunable rare-earth doped-fiber laser is configured as a ring and is capable of being used both as a downstream laser source at the central office (CO) of an optical fiber network and as a wavelength-selecting injection source for the upstream lasers at the subscriber site. The fiber laser is constructed based on optical filtering, polarization control and noise suppression techniques. An example is shown by using an optical polarization controller, a semiconductor optical amplifier, and an optical tunable filter. Moreover, it is wavelength tunable and can be applied to dynamic wavelength assignment networks. The fiber laser having a tunable wavelength range in the C band (and/or L band) are adopted for the Fabry-Pérot lasers working in the C-band (and/or L band). The passive optical network is employed to link the fiber laser and Fabry-Pérot lasers (or vertical-cavity surface-emitting lasers) injection-locked by the fiber laser. Downstream wavelength at the subscriber site is selected by an optical demultiplexer or wavelength router. A circulator is employed for the flow control of the downstream and upstream signals. Downstream signal at 10 Gb/s and upstream signal at 1.25 Gb/s can be transmitted over 10-km single-mode fiber with power penalties of 0.9 dB and 0.5 dB, respectively. A longer transmission distance is also possible.
Accordingly, the present invention discloses a bidirectional transmission network apparatus based on a tunable rare-earth-doped fiber laser to achieve high-speed data transmission with lowered manufacturing cost. Therefore, the present invention is novel, useful and non-obvious.
Although this invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments that will be apparent to persons skilled in the art. This invention is, therefore, to be limited only as indicated by the scope of the appended claims.
