Abstract
A method and apparatus for signal processing by light waveform shaping are provided to process an uplink signal generated by a digital-to-analog converter (DAC) and/or process a downlink signal to be transmitted to an analog-to-digital converter (ADC). The method includes adjusting the waveform of the uplink signal and/or the waveform of the downlink signal with a light waveform shaping module so that, even if the DAC and/or ADC has a low sampling rate and a narrow bandwidth, a high-frequency signal portion of the uplink signal and/or a high-frequency signal portion of the downlink signal can be preserved.
Claims
1-8. (canceled)
9. An apparatus for signal processing by light waveform shaping, comprising: a digital-to-analog converter generating an uplink signal; an analog-to-digital converter receiving a downlink signal; and a light waveform shaper separately and electrically connected to the digital-to-analog converter and the analog-to-digital converter and processing at least one of the uplink signal and the downlink signal, the light waveform shaper including an optical modulation subsystem and an optical gating, the optical modulation subsystem turning the uplink signal into a light pulse signal and thereby preventing suppression of a high-frequency image signal portion of the uplink signal, and the optical gating suppressing inter-sample interference of the downlink signal and thereby eliminating a low-pass effect in order to preserve aliasing between a high-frequency signal portion and a low-frequency signal portion of the downlink signal.
10. The apparatus of claim 9, wherein each of the optical modulation subsystem and the optical gating includes at least one optical modulator, and the at least one optical modulator of the optical modulation subsystem or the optical gating is one or an arbitrary combination of an electro-absorption modulator, a Mach-Zehnder interferometer, a gain-switching (GS) pulse laser diode, and a semiconductor optical amplifier.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0014] FIG. 1 is a system block diagram of an embodiment of the present invention;
[0015] FIG. 2 is a schematic circuit diagram of the embodiment in FIG. 1;
[0016] FIG. 3 is another schematic circuit diagram of the embodiment in FIG. 1;
[0017] FIG. 4 schematically shows how an uplink signal is processed by the embodiment in FIG. 1; and
[0018] FIG. 5 schematically shows how a downlink signal is processed by the embodiment in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention incorporates the foregoing technical features into a method and apparatus for signal processing by light waveform shaping. The major effects of the method and apparatus can be readily understood by reference to the embodiment described below, where the DDM-OFDMA PON technique is applied by way of example.
[0020] Referring to FIG. 1 and FIG. 2, a central office (CO) A is connected to at least one optical network unit (ONU) 10 via a single-mode optical fiber B. Each ONU 10 includes one apparatus of the present invention for processing signals by light waveform shaping. The apparatus of the present invention includes a low-sampling-rate (LSR), narrow-bandwidth digital-to-analog converter (DAC) 1, an LSR narrow-bandwidth analog-to-digital converter (ADC) 2, and a light waveform shaping module 3. The DAC 1 is configured to generate an uplink signal while the ADC 2 is configured to receive a downlink signal.
[0021] As shown in FIG. 1 and FIG. 2, the light waveform shaping module 3 is separately and electrically connected to the DAC 1 and the ADC 2 and is configured to process the uplink signal and/or the downlink signal. The light waveform shaping module 3 includes an optical modulation module 31 and an optical gating 32. As shown in FIG. 2 and FIG. 4, the optical modulation module 31 is configured to turn the uplink signal into a light pulse signal 302, thereby preventing a high-frequency image signal portion of the uplink signal from be suppressed. As shown in FIG. 3 and FIG. 5, the optical gating 32 is configured to suppress inter-sample interference 301 of the downlink signal so that the low-pass effect is eliminated to preserve aliasing between a high-frequency signal portion and a low-frequency signal portion of the downlink signal.
[0022] More specifically, with continued reference to FIG. 2 and FIG. 4, the optical modulation module 31 includes at least one optical modulator, which in this embodiment includes an electro-absorption modulator (EAM) 311. The EAM 311 is optically connected to a light pulse source 300 and is configured to generate the light pulse signal 302 by modulating the light pulse source 300. The light pulse source 300 may be generated by a Mach-Zehnder interferometer 312, another EAM 313, or a gain-switching (GS) pulse laser diode 314. The Mach-Zehnder interferometer 312 and the EAM 313 are respectively and optically connected to continuous-wave (CW) laser diodes 315 and 316 and are electrically connected to a sine-wave oscillator 30. The GS pulse laser diode 314 is also electrically connected to the sine-wave oscillator 30. The sine-wave oscillator 30 serves to either directly drive the GS pulse laser diode 314 to generate the light pulse source 300, or drive the Mach-Zehnder interferometer 312 and the EAM 313 to modulate the CW laser diodes 315 and 316 respectively in order to generate the light pulse source 300.
[0023] As shown in FIG. 3, the optical gating 32 includes at least one optical modulator, which in this embodiment includes a Mach-Zehnder interferometer 321, an EAM 322, and a semiconductor optical amplifier (SOA) 323. The Mach-Zehnder interferometer 321, the EAM 322, and the SOA 323 are all connected to the sine-wave oscillator 30. The sine-wave oscillator 30 controls losses of the Mach-Zehnder interferometer 321 and the EAM 322 or gain of the SOA 323 in order to turn on or off the downlink signal (i.e., the light waveform shaping operation). Moreover, the optical gating 32 is connected to an optical band-pass filter (OBPF) 324 and a photodetector 325. The OBPF 324 serves to filter out optical noise and may be dispensed with if so desired.
[0024] The above description of the embodiment should be able to enable a full understanding of the operation, use, and effects of the present invention. The embodiment, however, is only a preferred one of the invention and is not intended to be restrictive of the scope of the invention. All simple equivalent changes and modifications made according to the appended claims and the disclosure of this specification should be encompassed by the invention.
