CN107664792B

CN107664792B - Optical signal generator, optical line terminal and method for generating optical signal

Info

Publication number: CN107664792B
Application number: CN201610608115.8A
Authority: CN
Inventors: 孙晓; 高震森; 昌庆江
Original assignee: Nokia Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2016-07-28
Filing date: 2016-07-28
Publication date: 2019-12-17
Anticipated expiration: 2036-07-28
Also published as: CN107664792A

Abstract

The present disclosure provides an optical signal generator, an optical line terminal, and a method of generating an optical signal. According to one embodiment of the present disclosure, an optical signal generator includes: at least one optical circuit comprising: a light source for generating an initial light signal; a first arrayed waveguide grating for demultiplexing the initial optical signal into a plurality of sub optical signals; a second arrayed waveguide grating for multiplexing the plurality of sub optical signals into a first optical signal; and a first optical coupler for splitting the first optical signal into a second optical signal and a third optical signal, outputting the second optical signal from the at least one optical loop, and feeding back the third optical signal to the optical source.

Description

Optical signal generator, optical line terminal and method for generating optical signal

Technical Field

The present invention relates generally to the field of optical communications, and more particularly, to an optical signal generator, an optical line terminal, and a method of generating an optical signal.

background

Ultra-wideband and its coexistence with existing technologies are fundamental requirements of network operators and will implement the evolution of Passive Optical Networks (PONs) according to such fundamental requirements. Existing PONs, such as GPON, EPON, and XG-PON, are based on Time Division Multiplexing (TDM) technology. However, in the near future, new business models (such as home video editing, online gaming, interactive E-learning, telemedicine services, and next generation 3D TV) will significantly increase the demand for bandwidth. A next-generation PON (NG-PON) will solve the above-described problems and also provide higher bandwidth and quality of service required for a specific service. Further, a time division wavelength division multiplexing passive optical network (TWDM-PON) by stacking a plurality of XG-PONs using Wavelength Division Multiplexing (WDM) has been selected as a main approach. A second way is to arrange a WDM PON that provides dedicated wavelength channels for individual Optical Network Units (ONUs) with different WDM transmission or reception techniques. Further technologies such as Orthogonal Frequency Division Multiplexing (OFDM) PON, 40Gbps TDMPON by employing advanced modulation techniques and radio over fiber (RoF) for Fi-wireless (Wi) access networks, and radio over fiber (RoF) are also possible for long term evolution. Therefore, it can be assumed that a coexistence system including an existing PON and an NG-PON having a plurality of services will be produced.

disclosure of Invention

to address at least in part the above and other potential problems, embodiments of the present disclosure propose an optical signal generator, an optical line terminal, and a method of generating an optical signal.

in a first aspect of the disclosure, an optical signal generator is provided. The optical signal generator includes: at least one optical circuit comprising: a light source for generating an initial light signal; a first arrayed waveguide grating for demultiplexing the initial optical signal into a plurality of sub optical signals; a second arrayed waveguide grating for multiplexing the plurality of sub optical signals into a first optical signal; and a first optical coupler for splitting the first optical signal into a second optical signal and a third optical signal, outputting the second optical signal from the at least one optical loop, and feeding back the third optical signal to the optical source.

according to one embodiment of the present disclosure, the at least one optical circuit includes a first optical circuit and a second optical circuit, wherein central wavelengths of channels of the first and second arrayed waveguide gratings in the first optical circuit and central wavelengths of channels of the first and second arrayed waveguide gratings in the second optical circuit are staggered from each other at a predetermined interval.

According to an embodiment of the present disclosure, the multi-wavelength light generator further includes: and a second optical coupler for combining the second optical signal output from the first optical circuit and the second optical signal output from the second optical circuit into a fourth optical signal to be output from the optical signal generator.

According to one embodiment of the present disclosure, the first and second arrayed waveguide gratings in the first and second optical circuits each have 32 channels, the channel spacing of the first and second arrayed waveguide gratings in the first and second optical circuits is about 200GHz, and the predetermined spacing is about 100 GHz.

According to one embodiment of the present disclosure, a light source includes a semiconductor optical amplifier.

according to one embodiment of the present disclosure, a semiconductor optical amplifier is based on increasing the gain of an initial optical signal by increasing the bias current applied to the semiconductor optical amplifier.

According to one embodiment of the present disclosure, the bias current is about 100 mA.

According to one embodiment of the present disclosure, the 3dB bandwidth of the channels of the first and second arrayed waveguide gratings is greater than 0.8 nm.

In a second aspect of the disclosure, an optical line terminal is provided. The optical line terminal includes: an optical signal generator according to a first aspect of the present disclosure; a demultiplexer for demultiplexing the optical signal output from the optical signal generator into a plurality of target optical signals; a plurality of modulators for modulating data to a plurality of target optical signals to generate a plurality of downstream optical signals; and a multiplexer for multiplexing the plurality of downlink optical signals into a first downlink optical signal to be transmitted to the optical network unit.

according to an embodiment of the present disclosure, the optical line terminal further includes: a distance extender for increasing a gain of the first downlink optical signal.

In a third aspect of the disclosure, a method of generating an optical signal is provided. The method comprises the following steps: at the at least one optical circuit: demultiplexing an initial optical signal generated by a light source into a plurality of sub optical signals by using a first arrayed waveguide grating; multiplexing the plurality of sub optical signals into a first optical signal using a second arrayed waveguide grating; splitting the first optical signal into a second optical signal and a third optical signal with a first optical coupler; feeding back the third optical signal to the light source; and outputting the second optical signal.

According to one embodiment of the disclosure, the method further comprises: combining the second optical signal output by the first optical circuit and the second optical signal output by the second optical circuit into a fourth optical signal; and outputting the fourth optical signal.

According to one embodiment of the disclosure, the method further comprises: a semiconductor optical amplifier is used as a light source.

according to one embodiment of the disclosure, the method further comprises: the gain of the original optical signal is increased by increasing the bias current applied to the semiconductor optical amplifier.

According to one embodiment of the disclosure, the method further comprises: the bias current is configured to be 100 mA.

according to one embodiment of the disclosure, the method further comprises: the 3dB bandwidths of the channels of the first and second arrayed waveguide gratings are configured to be greater than 0.8 nm.

as will be understood from the following description, the optical signal generator and the optical signal generating method according to the present disclosure can be applied to and support coexistence of all modulation techniques and multi-generation multi-service PONs, and also support a network architecture of "pay-per-growth-cost" (pay as you grow). The corresponding benefits will be described in detail below.

Drawings

The present disclosure will be better understood and other objects, details, features and advantages thereof will become more apparent from the following description of specific embodiments of the present disclosure, which is given by reference to the following drawings. In the drawings:

FIG. 1 shows a schematic diagram of an optical signal generator 10 according to one embodiment of the present disclosure;

Figure 2 shows a schematic diagram of an optical network architecture 20 according to one embodiment of the present disclosure;

FIG. 3 shows a schematic diagram of an optical signal generator 30 according to another embodiment of the present disclosure;

FIG. 4 shows a flow diagram of a method 400 of generating an optical signal according to one embodiment of the present disclosure;

FIG. 5 shows a schematic diagram of the spectral response of an arrayed waveguide grating having 200GHz spacing according to one embodiment of the present disclosure;

FIG. 6 shows a schematic output spectrum of Dense WDM (DWDM) channels at different bias currents of a semiconductor optical amplifier according to one embodiment of the present disclosure;

FIG. 7 shows a schematic output spectrum of DWDM channels at different 3dB bandwidths of an arrayed waveguide grating according to one embodiment of the present disclosure;

FIG. 8 shows a schematic generation of 64 DWDM wavelength channels according to one embodiment of the present disclosure;

FIG. 9a shows a receive eye diagram of 2.5Gb/s OOK after 20km of single longitudinal mode fiber transmission according to one embodiment of the present disclosure;

FIG. 9b shows a receive eye diagram of 10Gb/s OOK after 20km of single longitudinal mode fiber transmission according to yet another embodiment of the present disclosure;

Figure 10 shows a received spectrum of a 16QAM OFDM signal after 20km of single longitudinal mode fiber transmission, according to another embodiment of the present disclosure; and

Figure 11 shows a constellation diagram of a recovered 16QAM OFDM signal after 20km of single longitudinal mode fiber transmission, according to one embodiment of the present disclosure.

Detailed Description

Example embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While certain exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

As described above, an optical signal generator is required to generate a series of optical sources and demultiplex for different modulation techniques, and thus the formed coexisting network can support the conventional TDM PON (e.g., GPON, EPON, XGPON) as well as the next generation optical access network (e.g., NG-PON, mobile fronthaul). The inventors have observed that the existing solutions have a number of drawbacks.

One existing solution is to employ WDM stacking. In downstream, different PON traffic services are mixed together and transmitted over the same Optical Distribution Network (ODN). Coexistence is ensured by a coexistence element that multiplexes/demultiplexes the various wavelengths associated with each generation of technology. Since the combined multi-generation PON or service requires different modulation techniques (e.g., binary on-off keying format (OOK), Quadrature Amplitude Modulation (QAM), and OFDM), external modulation using seed light is required. This requires high quality of service and a large number of light sources to be deployed for each PON service.

further, the best way to provide the light source is to use a laser array of multiple wavelengths, such as a Distributed Feedback (DFB) laser and a fabry-perot (FP-LD) laser array. For a co-existence system, this is an alternative to providing a single coherent light as the light source for the Optical Line Terminal (OLT). However, it is not easy to manufacture high-performance multi-wavelength laser arrays. First, the different lasers, which are evenly spaced, must be defined laterally on the wafer side. This is often done by electron beam lithography, Multiple Quantum Well (MQW) selective area growth, and ridge width variation. Also, all of these techniques have difficulty achieving uniform wavelength intervals and may generate polygonal modes. Second, the emissions from different laser elements should be collected into a single waveguide before being coupled to a Single Mode Fiber (SMF) for transmission in a PON. However, it is very difficult to achieve high coupling efficiency, so that this will usually end up with low output power. Finally, wavelength accuracy and wavelength drift issues need to be overcome because the wavelength of DFB lasers is very sensitive to chip temperature.

On the other hand, the coexisting network system is designed as a "pay as you grow" to allow operators to set up different technologies, and thus the entire WDM network typically requires a minimum of 64 wavelengths. This would obviously increase the difficulty of laser array fabrication and the cost of development.

all these cases thus indicate that conventional solutions require high quality of service and a large number of light sources, low coupling efficiency, temperature sensitivity and high manufacturing and development costs. To address, at least in part, the above and other potential problems, embodiments of the present disclosure propose new optical signal generation devices and methods.

Fig. 1 shows a schematic diagram of an optical signal generator 10 according to one embodiment of the present disclosure. As shown in fig. 1, the optical signal generator 10 includes at least one optical circuit, only one optical circuit 105 being shown in fig. 1 for clarity. The operation principle of the remaining optical circuits, not shown, is similar to that of the optical circuit.

The optical circuit 105 includes a light source 110, a first arrayed waveguide grating 120, a second arrayed waveguide grating 130, and a first optical coupler 140. The light source 110 is used to generate an initial light signal. In one embodiment of the present disclosure, the light source 110 may be a self-gain, broadband radiation source, such as a Semiconductor Optical Amplifier (SOA). Thus, the initial optical signal emitted by the optical source 110 has a broadband Amplifier Spontaneous Emission (ASE) spectrum. In the case of using an SOA as the optical source 110, the gain of the initial optical signal may be increased to overcome the losses in the optical loop 105 based on increasing the bias current applied to the SOA. In one embodiment of the present disclosure, the bias current is about 100 mA. Of course, it should be understood that the above implementations are merely exemplary, and that any other suitable type of light source and/or bias current value may be employed.

The first arrayed waveguide grating 120 demultiplexes the initial optical signal into a plurality of sub optical signals. Here, the original optical signal is spectrally sliced into a plurality of sub optical signals by the first arrayed waveguide grating 120. The interval of each sub-optical signal corresponds to the channel interval of the first arrayed waveguide grating 120. Subsequently, the second arrayed waveguide grating 130 multiplexes the plurality of sub optical signals into the first optical signal. In one embodiment of the present disclosure, the 3dB bandwidth of the channels of the first and second arrayed waveguide gratings 120 and 130 is greater than 0.8 nm. Further, the first optical coupler 140 splits the first optical signal into a second optical signal and a third optical signal, outputs the second optical signal from the at least one optical loop, and feeds back the third optical signal to the optical source 110.

the optical circuit 105 forms an external laser cavity that, after settling, produces a stable coherent multi-wavelength laser as a subsequently used multi-wavelength optical signal. Here, the steady state means that the gain of the light source itself and the loss of each element in the optical circuit reach a steady state.

Further, in the case where the optical signal generator 10 includes a plurality of optical circuits, the central wavelengths of the channels of the first and second arrayed waveguide gratings in each optical circuit are shifted from each other at predetermined intervals with respect to the central wavelengths of the channels of the first and second arrayed waveguide gratings in the other optical circuits.

For example, consider two optical circuits included in optical signal generator 10, referred to as a first optical circuit and a second optical circuit. The central wavelengths of the channels of the first and second arrayed waveguide gratings 120 and 130 in the first optical circuit and the central wavelengths of the channels of the first and second arrayed waveguide gratings 120 and 130 in the second optical circuit are staggered from each other at predetermined intervals.

Figure 2 shows a schematic diagram of an optical network architecture 20 according to one embodiment of the present disclosure. As shown in fig. 2, the optical network architecture 20 includes at least one Optical Line Terminal (OLT)210, a wavelength switching router 240, a remote node 245, and a plurality of Optical Network Units (ONUs) 255, 260, and 265.

the connection and number of the above components are only shown by way of example, and it should be understood by those skilled in the art that the above number is only illustrative and not restrictive. For example, although only 3 ONUs are shown in fig. 2, any number of ONUs may be configured according to actual needs.

In the OLT 210 shown in fig. 2, an optical signal generator 215 according to the present disclosure, such as the optical signal generator 10 described with reference to fig. 1, is included. In addition, the OLT 210 comprises a demultiplexer 220, at least one modulator 225, a multiplexer 230.

The optical signal generator 215 will generate an optical signal at multiple wavelengths. The optical signal of the multiple wavelengths is demultiplexed to a plurality of target optical signals via the demultiplexer 220. In one embodiment of the present disclosure, the demultiplexer 220 may be, for example, an arrayed waveguide grating having a number of channels corresponding to the number of target optical signals.

these target optical signals are then provided to at least one modulator 225. The modulators 225 may be of the same type or different types. For example, modulator 225 may be an I/Q modulator, an intensity modulator, or an analog modulator. And different modulators 225 may also be used to modulate different types of data, e.g., OFDM, OOK, etc. The modulators are used to modulate data onto a plurality of target optical signals to produce a plurality of downstream optical signals. Next, the multiplexer 230 multiplexes the plurality of downlink optical signals into a first downlink optical signal to be transmitted to the ONU.

in one embodiment of the present disclosure, the OLT 210 may further include a distance extender 235 for increasing a gain of the first downlink optical signal, thereby increasing a transmission distance of the first downlink optical signal. In one embodiment of the present disclosure, the distance extender 235 may include at least one of an optical fiber amplifier (EDFA), an SOA, a wave shaper.

The first downstream optical signal, which is output by the OLT 210, will be transported to a different remote node 245, e.g. via a wavelength-switched router 240. Then further transported to a plurality of ONUs 255, 260 and 265 by splitter 250 in remote node 245. These ONUs may be based on the same technology or may be based on different technologies. For example, ONU 255 is a GPONONU, ONU 260 is an XGPON ONU, and ONU 265 is an NG-PON ONU. Therefore, the optical signal generator according to the present disclosure may be applied to modulation schemes, data types, PON services, and ONUs of different technology types, and thus may be used in an environment where multi-generation technologies coexist.

fig. 3 shows a schematic diagram of an optical signal generator 30 according to another embodiment of the present disclosure. The optical signal generator 30 shown in fig. 3 may be used as the optical signal generator in the OLT 210 in fig. 2 to generate an optical signal at multiple wavelengths. The optical signal generator 30 shown in fig. 3 has a first optical circuit 105, a second optical circuit 305 and a second optical coupler 310.

in this implementation, the first optical circuit 105 includes a light source 110, a first arrayed waveguide grating 120, a second arrayed waveguide grating 130, and a first optical coupler 140. The second optical circuit 305 includes the light source 110, the first arrayed waveguide grating 120, the second arrayed waveguide grating 130, and the first optical coupler 140.

In this embodiment, the first and second arrayed waveguide gratings 120 and 130 having 32 channels are exemplarily used in the first and second optical circuits 105 and 305. The channel spacing of the first and second arrayed waveguide gratings 120 and 130 is about 200 GHz. Further, the central wavelengths of the channels of the first and second arrayed waveguide gratings 120 and 130 in the first optical circuit 105 and the central wavelengths of the channels of the first and second arrayed waveguide gratings 120 and 130 in the second optical circuit 305 are staggered from each other at a predetermined interval of about 100 GH.

as previously described, the two light sources 110 in the first optical circuit 105 and the second optical circuit 305 may be a self-gain, broadband radiation source, such as an SOA. Thus, the initial optical signal emitted by the optical source 110 has a broadband Amplifier Spontaneous Emission (ASE) spectrum.

As shown in fig. 3, for the first optical circuit 105, the first arrayed waveguide grating 120 demultiplexes the original optical signal into 32 sub optical signals (Ch1, Ch3 … Ch 63). Subsequently, the second arrayed waveguide grating 130 multiplexes the 32 sub optical signals (Ch1, Ch3 … Ch63) into the first optical signal of multiple wavelengths. The first optical signal has 32 wavelengths (these wavelengths are shown in the figure as block diagrams with different lines). The first optical coupler 140 splits the first optical signal into a second optical signal and a third optical signal, outputs the second optical signal from the first optical loop 105, and feeds back the third optical signal to the optical source 110. As previously described, the first optical circuit 105 forms a laser cavity that, after settling, will produce a stable coherent laser light as an optical signal at a plurality of wavelengths for subsequent use.

Similarly, for the second optical circuit 305, the first arrayed waveguide grating 120 demultiplexes the original optical signal into 32 sub optical signals (Ch2, Ch4 … Ch 64). Subsequently, the second arrayed waveguide grating 130 multiplexes the 32 sub optical signals (Ch2, Ch4 … Ch64) into the first optical signal of multiple wavelengths. Here, the first optical signal in the second optical circuit 305 also has 32 wavelengths (these wavelengths are shown in the diagram with different lines). The first optical coupler 140 splits the first optical signal into a second optical signal and a third optical signal, outputs the second optical signal from the second optical loop 305, and feeds back the third optical signal to the optical source 110. Similarly, the second optical circuit 305 forms a laser cavity that, after settling, produces a stable coherent laser light for subsequent use as an optical signal at multiple wavelengths.

The second optical coupler 310 combines the second optical signal from the first optical circuit 105 and the second optical signal from the second optical circuit 305 into a fourth optical signal to be output from the optical signal generator 30. As shown, the optical signal finally output by the optical signal generator 30 has 64 wavelengths (the wavelengths are shown in the figure as block diagrams with different lines), and the respective wavelengths are spaced apart from each other at 100 GHz.

in this embodiment, the central wavelengths of the channels of the arrayed waveguide gratings in the first optical loop 105 and the second optical loop 305 are staggered by 100GHz, and the outputs of the two optical loops are combined together by the second optical coupler 310. This doubles the sum of the number of all wavelengths and it fully meets the standards of the intensive wdm (dwdm) International Telecommunications Union (ITU).

It should be understood by those skilled in the art that while an implementation of two optical circuits is shown in the embodiment of fig. 3, the above description is merely exemplary and not limiting. An optical signal generator according to the present disclosure may include any number of optical circuits, and the principles of operation of the two optical circuits described herein may be extended to any desired number of optical circuits. For example, 64 wavelengths of optical signals are generated in the embodiment of fig. 3, and the number of wavelengths of the optical signals output by the optical signal generator can be extended by setting the required number of optical loops. Similarly, all numerical values described above are exemplary only, and are not intended to limit the scope of the present disclosure in any way.

Fig. 4 shows a flow diagram of a method 400 of generating an optical signal according to one embodiment of the present disclosure. The method of fig. 4 will be described below in conjunction with fig. 1, with the method of fig. 4 being implemented at the at least one optical circuit 105.

at 410, an initial optical signal generated by the optical source 110 is demultiplexed into a plurality of sub-optical signals using the first arrayed waveguide grating 120. At 420, the plurality of sub optical signals are multiplexed into the first optical signal using the second arrayed waveguide grating 130. At 430, the first optical signal is split into a second optical signal and a third optical signal using the first optical coupler 140. At 440, the third optical signal is fed back to the optical source 110. At 450, a second optical signal is output.

although fig. 4 shows only a few steps of method 400, it should be understood that method 400 may also contain a number of optional steps not shown. For example, in some embodiments, the at least one optical circuit includes a first optical circuit and a second optical circuit, wherein the central wavelengths of the channels of the first and second arrayed waveguide gratings in the first optical circuit and the central wavelengths of the channels of the first and second arrayed waveguide gratings in the second optical circuit are staggered from each other by a predetermined interval.

In some embodiments, the method further comprises combining the second optical signal output by the first optical circuit and the second optical signal output by the second optical circuit into a fourth optical signal; and outputting the fourth optical signal. In some embodiments, the first and second arrayed waveguide gratings in the first and second optical circuits each have 32 channels, the channel spacing of the first and second arrayed waveguide gratings in the first and second optical circuits is about 200GHz, and the predetermined spacing is about 100 GHz.

In certain embodiments, the method further comprises: a semiconductor optical amplifier is used as a light source. In certain embodiments, the method further comprises: the gain of the original optical signal is increased by increasing the bias current applied to the semiconductor optical amplifier. In certain embodiments, the method further comprises: the bias current is configured to be 100 mA. In certain embodiments, the method further comprises: the 3dB bandwidths of the channels of the first and second arrayed waveguide gratings are configured to be greater than 0.8 nm.

Various advantages of the optical signal generator and benefits from various components according to the present disclosure will be verified with reference to the figures below. For this reason, detailed experimental methods were implemented to simulate multiple PON services. As will be described in detail below, the optical signal generated by the optical signal generator as a multi-wavelength optical source is capable of being qualified for error rate-free 10Gb/s OOK, 10Gb/s 16QAM, and 10Gb/s OFDM modulation over transmission of single longitudinal mode (SMF) fiber exceeding 20 km. This indicates that the proposed light source can support all PON services from the conventional TDM/TWDM/WDM PON to the advanced OFDM PON and the mobile fronthaul service.

In certain embodiments of the present disclosure, an arrayed waveguide grating (e.g., the first arrayed waveguide gratings 330 and 340, the second arrayed waveguide gratings 350 and 360 in fig. 3) having a channel spacing of 200GHz is used in the optical signal generator. The reason for using such an arrayed waveguide grating is that the 3dB bandwidth of each wavelength channel can be significantly increased, allowing more light to pass through the channels of the arrayed waveguide grating. Thus, in the aforementioned external laser resonator, the total gain exceeds the total loss, thereby increasing the intensity of the laser.

in contrast, if a conventional 100GHz channel spaced arrayed waveguide grating is used, no laser light is generated, and only incoherent ASE noise sliced in the spectrum is obtained. The reason is that: such light sources are too wide for telecommunication and can only be used for transmitting low power signals.

Figure 5 shows a spectral response diagram of an arrayed waveguide grating having a 200GHz spacing according to one embodiment of the present disclosure. As shown in FIG. 5, the channel spacing is 200GHz (or ≈ 1.6nm), the 3dB bandwidth per channel is 1nm and the channel compression ratio is 20 dB. Further, such an arrayed waveguide grating is easy to manufacture. The channel response of a flat-topped arrayed waveguide grating is better than that of a gaussian or triangular shape because lasing is easier. This problem will be described in detail below.

Fig. 6 shows an output spectrum diagram of dense wdm (dwdm) channels at different bias currents of a semiconductor optical amplifier according to one embodiment of the present disclosure. The output spectrum at different bias currents is shown in fig. 6 with different lines. An ITU DWDM channel (ch.20, 1561.42nm) is here exemplarily selected as the DWDM channel. As shown in fig. 6, at low SOA bias current (20mA), the output spectrum is ASE noise with slices of the same shape as the channels of the arrayed waveguide grating. However, as the SOA bias current increases, the laser light rises due to the overall gain increase in the external laser cavity. When the SOA is biased at 100mA, a maximum output power around-5 dBm is obtained and the corresponding SNR is 65 dB.

Figure 7 shows a schematic output spectrum of DWDM channels at different 3dB bandwidths of an arrayed waveguide grating according to one embodiment of the present disclosure. Similarly, an ITU DWDM channel (Ch.20, 1561.42nm) is illustratively selected as the DWDM channel. Further, in the example of fig. 7, the bias current of the SOA is 100 mA. Here, the output spectra at different 3dB bandwidths of the arrayed waveguide grating are shown in different lines.

As shown in fig. 7, when the 3dB bandwidth of the arrayed waveguide grating is greater than 0.8nm, lasing occurs and the peak power remains stable regardless of the 3dB bandwidth of the subsequent channel. As shown in fig. 7, the center wavelength is red-shifted at the 3dB bandwidth of the larger channel due to the cross-gain caused by the interaction between the multiple longitudinal modes. The spectral red-shift indicates that the long-wavelength mode (long-wavelength mode) experiences higher optical gain. Therefore, it is better to use a flat-topped arrayed waveguide grating than a gaussian-shaped arrayed waveguide grating. This is because: if a gaussian-shaped arrayed waveguide grating is used, the red shift is affected by a large frequency response attenuation caused by the falling edge of the long wavelength of the gaussian-shaped arrayed waveguide grating. A flat-topped arrayed waveguide grating can just avoid the above problems.

Figure 8 shows a schematic diagram of the generation of 64 DWDM wavelength channels according to one embodiment of the present disclosure. In FIG. 8, two sets of 1:32 arrayed waveguide gratings with a channel spacing of 200GHz and a 3dB channel bandwidth of 1nm were used to produce a total of 64 coherent light sources. This may be achieved, for example, by the optical signal generator 30 shown in fig. 3. For example, 32 wavelengths (shown in solid lines in fig. 8) are generated by the first optical loop of the optical signal generator 30, while the remaining 32 wavelengths (shown in dashed lines in fig. 8) are generated by the second optical loop of the optical signal generator 30.

Thereby obtaining a total of 64 wavelengths. All these wavelength channels have a moderate power of-5 dBm and a very high SNR above 65 dB. Because the arrayed waveguide grating (e.g., the first arrayed waveguide grating 120, 330, and 340) is used in the present disclosure to determine the wavelength spacing and because the arrayed waveguide grating is insensitive to temperature, the wavelength accuracy and wavelength drift issues can be significantly improved over prior art multi-wavelength laser arrays.

Further, as shown in fig. 8, the entire wavelength range of the generated optical signal of multiple wavelengths is from 1525nm to 1575nm, which completely covers the C bandwidth. Furthermore, as mentioned before, the total number of wavelength channels can also be improved by employing a higher ratio of arrayed waveguide gratings, and this will meet the downstream wavelength standard of all existing PON services and NG-PON services.

The signal modulation performance of optical signal generators (e.g., optical signal generators 10 and 30) in accordance with the present disclosure will be further elucidated by the figures. Here, one of the optical signals/light sources generated by the optical signal generator is selected and a modulator (e.g., modulator 230 in fig. 2) is used to modulate the OOK data signal and the OFDM data signal thereon to emulate the conventional TDM PON and NG-PON traffic. FIG. 9a shows a receive eye diagram of 2.5Gb/s OOK after 20km of single longitudinal mode fiber transmission, according to one embodiment of the present disclosure. Figure 9b shows a receive eye diagram of 10Gb/s OOK after 20km of single longitudinal mode fiber transmission according to yet another embodiment of the present disclosure.

With the optimum sensitivity of the receiver at-28 dBm, both eyes remain unfolded and open, and the measured bit error rate is less than 10, as shown in fig. 9a and 9b^-9. This transmission performance is comparable to the DFB + Electro Absorption Modulator (EAM) configuration and also does not require a temperature control mechanism. Thereby enabling further cost savings.

Further, OFDM transmission performance was also measured by modulating the 2.5GHz 16QAM OFDM signal. Fig. 10 shows a received spectrum of a 16QAM OFDM signal after 20km of single longitudinal mode fiber transmission according to another embodiment of the present disclosure. Fig. 11 shows a constellation diagram of a recovered 16QAMOFDM signal after 20km of single longitudinal mode fiber transmission according to one embodiment of the present disclosure. As shown in fig. 10, the recovered spectrum is extremely clear without being disturbed by noise, and the signal constellation in fig. 11 is also clear. With an optimum sensitivity of the receiver of-20 dBm, the average error vector magnitude at the OFDM signal is below 12.5%.

Therefore, the above experimental results indicate that the proposed optical signal generator can provide a large number of high quality optical sources, which can be used for modulation of all services in a coexistence situation of a multi-service PON system.

The present disclosure proposes an optical signal generator, an optical line terminal, and a method of generating an optical signal. The proposed solution has at least the following advantages: 1) the method can be suitable for coexistence of all modulation technologies and multi-generation and multi-service PON; 2) a network architecture supporting "pay as you grow"; 3) a plurality of coherent light sources can be provided. Further, compared to the conventional solution, the solution has at least the following advantages: 1) easy to manufacture and easy to centralize control/management; 2) low cost and low power consumption: in this scheme only the SOA is the active component, the AWG and the optocoupler are the passive components; 3) accurate wavelength spacing is achieved; 4) is not sensitive to temperature and has no wavelength drift problem; 5) an ultra-high SNR is achieved.

due to future PON evolution, existing PON ODN architectures need to be inherited. This will lead to the coexistence of multi-service PONs with different modulation techniques in the same ODN network. High performance multi-wavelength light sources will become very important and the present disclosure addresses at least the above problems.

In one or more exemplary designs, the functions of this application may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. Such computer-readable media can comprise, for example, but is not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code means in the form of instructions or data structures and which can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium.

the various illustrative logical blocks, modules, and circuits described in connection with the disclosure may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An optical signal generator comprising:

At least one optical circuit comprising:

A light source for generating an initial light signal;

A first arrayed waveguide grating for demultiplexing the initial optical signal into a plurality of sub optical signals;

A second arrayed waveguide grating for multiplexing the plurality of sub optical signals into a first optical signal; and

A first optical coupler to split the first optical signal into a second optical signal and a third optical signal, output the second optical signal from the at least one optical loop, and feed back the third optical signal to the optical source.

2. The optical signal generator of claim 1, wherein the at least one optical circuit includes a first optical circuit and a second optical circuit, and the central wavelengths of the channels of the first and second arrayed waveguide gratings in the first optical circuit and the central wavelengths of the channels of the first and second arrayed waveguide gratings in the second optical circuit are staggered from each other by a predetermined interval.

3. the optical signal generator of claim 2, further comprising:

a second optical coupler for combining the second optical signal output by the first optical circuit and the second optical signal output by the second optical circuit into a fourth optical signal to be output from the optical signal generator.

4. the optical signal generator of claim 3, wherein the first and second arrayed waveguide gratings in the first and second optical circuits each have 32 channels, the channel spacing of the first and second arrayed waveguide gratings in the first and second optical circuits is 200GHz, and the predetermined spacing is 100 GHz.

5. The optical signal generator of claim 1, wherein the optical source comprises a semiconductor optical amplifier.

6. the optical signal generator of claim 5, wherein the semiconductor optical amplifier is based on increasing the gain of the initial optical signal by increasing a bias current applied to the semiconductor optical amplifier.

7. The optical signal generator of claim 6, wherein the bias current is 100 mA.

8. The optical signal generator of claim 1, wherein the 3dB bandwidth of the channels of the first and second arrayed waveguide gratings is greater than 0.8 nm.

9. An optical line terminal comprising:

An optical signal generator according to any one of claims 1 to 8;

A demultiplexer for demultiplexing the optical signal output from the optical signal generator into a plurality of target optical signals;

A plurality of modulators for modulating data to the plurality of target optical signals to generate a plurality of downstream optical signals; and

A multiplexer for multiplexing the plurality of downlink optical signals into a first downlink optical signal for transmission to an optical network unit.

10. The optical line terminal of claim 9, further comprising:

a distance extender for increasing a gain of the first downlink optical signal.

11. a method of generating an optical signal, comprising:

At the at least one optical circuit:

Demultiplexing an initial optical signal generated by a light source into a plurality of sub optical signals by using a first arrayed waveguide grating;

Multiplexing the plurality of sub optical signals into a first optical signal using a second arrayed waveguide grating;

Splitting the first optical signal into a second optical signal and a third optical signal with a first optical coupler;

feeding back the third optical signal to the light source; and

And outputting the second optical signal.

12. the method of claim 11, wherein the at least one optical circuit comprises a first optical circuit and a second optical circuit, wherein the central wavelengths of the channels of the first and second arrayed waveguide gratings in the first optical circuit and the central wavelengths of the channels of the first and second arrayed waveguide gratings in the second optical circuit are staggered from each other by a predetermined interval.

13. The method of claim 12, wherein the method further comprises:

Combining the second optical signal output by the first optical loop and the second optical signal output by the second optical loop into a fourth optical signal; and

Outputting the fourth optical signal.

14. The method of claim 13, wherein the first and second arrayed waveguide gratings in the first and second optical circuits each have 32 channels, the channel spacing of the first and second arrayed waveguide gratings in the first and second optical circuits is 200GHz, and the predetermined spacing is 100 GHz.

15. The method of claim 11, further comprising:

A semiconductor optical amplifier is used as the light source.

16. The method of claim 15, further comprising:

the gain of the initial optical signal is increased by increasing the bias current applied to the semiconductor optical amplifier.

17. The method of claim 16, further comprising:

The bias current is configured to be 100 mA.

18. The method of claim 11, further comprising:

Configuring a 3dB bandwidth of channels of the first and second arrayed waveguide gratings to be greater than 0.8 nm.