Fiber communication systems and methods

Abstract

Injection-locked transmitter for an optical communications network, comprising: a master seed laser source input that is limited to a single longitudinal mode; an input data stream; and a laser-injected modulator comprising at least one slave laser with a resonator frequency locked to a frequency of the single longitudinal mode of the master-seed laser source, wherein the laser-injected modulator is configured to receive the master-seed laser source input and the input data stream and to output a laser-modulated data stream, characterized by the fact that the transmitter further comprises: a first optical circulator in communication with the laser-injected modulator and the master-seed laser source input; a second optical circulator in one-way communication with the first optical circulator and in two-way communication with the at least one slave laser; and an external modulation element located between the first optical circulator and the second optical circulator, wherein the external modulation element is configured to receive the input data stream and an output from the second optical circulator, where the first optical circulator is in one-way communication with an output of the external modulation element.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from US 2017 / 0294966A1, filed on October 3, 2016, which claims priority from US Provisional Patent Application Ser. No. 62 / 321,211, filed on April 12, 2016. BACKGROUND

[0002] The field of disclosure generally relates to fiber communication networks, and in particular to optical networks that use wavelength division multiplexing.

[0003] Telecommunications networks include an access network through which end users connect to a service provider. Bandwidth requirements for delivering high-speed data and video services over the access network are increasing rapidly to meet growing consumer demands. Currently, data delivery over the access network is increasing by gigabits (Gb) per second for residential customers and by multi-Gb / s for business customers. Today's access networks are based on passive optical network access (PON) technologies, which have become the dominant system architecture to meet the growing high-capacity demands of end users.

[0004] Gigabit PON and Ethernet PON architectures are conventionally known and currently offer approximately 2.5 Gb / s downstream data rates and 1.25 Gb / s upstream data rates (half the downstream rate). 10 Gb / s PON (XGPON or IEEE 10G-EPON) has begun to be implemented for high-bandwidth applications, and a 40 Gb / s PON scheme based on time-division multiplexing (TWDM) and wavelength-division multiplexing (WDM) has recently been standardized. Therefore, there is a growing need to develop higher / faster data rates per subscriber to meet future bandwidth demands, as well as to increase service and application coverage while minimizing the capital and operating costs required to deploy higher-capacity, high-performance access networks.

[0005] A well-known solution for increasing the capacity of a PON is the use of WDM technology to send a dedicated wavelength signal to the end user. However, the current detection scheme of WDM technology is limited by low receiver sensitivity and the limited upgrade and scalability of the technology, especially when used in conjunction with the existing, low-quality legacy fiber environment. The existing legacy fiber environment requires operators to extract more capacity from the existing fiber infrastructure to avoid the costs associated with reducing new fiber installations. Traditional access networks typically consist of six fibers per node and serve up to 500 end users, such as residential customers.Conventional nodes cannot be further subdivided and typically do not contain free (unused) fibers, so it is necessary to use the limited fiber availability more efficiently and cost-effectively.

[0006] Coherent technology has been proposed as a solution to increase both receiver sensitivity and overall capacity for optical WDM-PON access networks in brownfield and greenfield distributions. Coherent technology offers excellent receiver sensitivity and an expanded power budget, as well as high-frequency selectivity that enables closely spaced, dense or ultra-dense WDM without the need for optical narrowband filters. Furthermore, the multidimensional recovered signal experienced by coherent technology provides additional benefits by overcoming linear transmission limitations such as chromatic dispersion (CD) and polarization mode dispersion (PMD), and by efficiently utilizing spectral resources to support future network upgrades and enhancements through the use of multi-level extended modulation formats.However, long-distance transmission using coherent technology requires extensive post-processing, including signal equalization and carrier recovery, to compensate for impairments along the transmission path, which presents significant challenges due to a considerably increased system complexity.

[0007] Coherent technology in long-range optical systems typically requires the use of high-quality discrete photonic and electronic components, such as digital-to-analog converters (DACs), analog-to-digital converters (ADCs), and digital signal processing (DSP) circuits, such as application-specific integrated circuits (ASICs) using CMOS technology, to compensate for noise, frequency drift, and other factors that affect the transmitted channel signals over long-range optical transmission. Coherent pluggable modules for metro solutions have undergone standardization from C Form-Factor Pluggable (CFP) to CFP2 and the future CFP4 via Multi-Source Agreement (MSA) to reduce their footprint, lower costs, and also reduce power dissipation.However, these modules still require significant technical complexity, cost, size and power to operate and were therefore not efficient or practical to implement in access applications.

[0008] US 2012 / 0087666A1 discloses a bidirectional WDM-PON. The bidirectional WDM-PON includes an optical comb generator, an amplifier, an optical deinterleaver, a downstream signal generator, an upstream signal generator, an upper circulator, and a lower circulator. The optical comb generator produces light at multiple wavelengths. The amplifier amplifies the multi-wavelength light. The optical deinterleaver receives the amplified multi-wavelength light to split the received light into an odd-wavelength train and an even-wavelength train, and outputs the odd-wavelength and even-wavelength trains. The downstream signal generator receives the odd-wavelength train to produce a downstream signal. The upstream signal receiver receives an upstream signal. The upper circulator determines a transmission path for the odd-wavelength train and the downstream signal.The lower circulator determines the transmission path of the straight wavelength train and the preceding signal.

[0009] US 2012 / 0 251 129 A1 discloses devices and methods for modulating an optical signal. One embodiment is a method comprising: phase modulation of a slave laser that is injection-locked to a master laser to generate an arc-phase modulated optical signal, and combination of the arc-phase modulated optical signal with an optical output signal of the master laser. BRIEF SUMMARY

[0010] In one aspect, an injection-locked transmitter for an optical communication network comprises a master-seed laser source input, which is essentially restricted to a single longitudinal mode, an input data stream, and a laser-injected modulator comprising at least one slave laser with a resonator frequency that is injection-locked to a frequency of the single longitudinal mode of the master-seed laser source. The laser-injected modulator is configured to receive the master-seed laser source input and the input data stream and to output a laser-modulated data stream.It is proposed that the transmitter further comprises a first optical circulator in communication with the laser-injected modulator and the master-seed laser source input; a second optical circulator in one-way communication with the first optical circulator and in two-way communication with the at least one slave laser; and an external modulation element arranged between the first optical circulator and the second optical circulator, wherein the external modulation element is configured to receive the input data stream and an output of the second optical circulator, and wherein the first optical circulator is in one-way communication with an output of the external modulation element.

[0011] In another aspect, an optical network communication system comprises an input signal source, an optical frequency comb generator configured to receive the input signal source and output a multitude of phase-synchronized coherence tone pairs. Each of the multitude of phase-synchronized coherence tone pairs comprises a first unmodulated signal and a second unmodulated signal. The system further comprises a first transmitter configured to transmit the first unmodulated signal of a selected phase-synchronized coherence tone pair as the seed.a seed source to receive and output a first modulated data stream, and a first receiver configured to receive the first modulated data stream from the first transmitter and to receive the second unmodulated signal of the selected one from the plurality of phase-synchronized coherence tone pairs as a local oscillator source, wherein the selected one from the plurality of phase-synchronized coherence tone pairs is controllable at a constant frequency interval from each other throughout the system.

[0012] In yet another aspect, an optical network communication system comprises an optical hub with an optical frequency comb generator, a downstream transmitter, and an optical hub multiplexer. The frequency comb generator is configured to output at least one phase-synchronized coherence tone pair with a first unmodulated signal and a second unmodulated signal. The system also includes a downstream transmitter configured to receive the first unmodulated signal as a seed source and output a downstream modulated data stream. Furthermore, the system comprises a fiber node and an end-user device with a downstream receiver configured to receive the downstream modulated data stream from the downstream transmitter and to receive the second unmodulated signal as a local oscillator source.The downstream transmitter is further configured to perform a polarization beam split of the first unmodulated phase-synchronized coherence tone before appending downstream data, and to append downstream data to the first unmodulated phase-synchronized coherence tone to generate the downstream modulated data stream. The optical hub multiplexer is configured to optically multiplex the first modulated data stream signal and the second unmodulated phase-synchronized coherence tone together.

[0013] In a further aspect, a method for processing an optical network comprises the steps of generating at least one pair of first and second unmodulated phase-synchronized coherence tones or coherent tones, transmitting the first unmodulated phase-synchronized coherence tone to a first transmitter as a seed signal, polarization beam splitting of the first unmodulated phase-synchronized coherence tone before appending downstream data, appending downstream data in the first transmitter to the first unmodulated phase-synchronized coherence tone to generate a first modulated data stream signal, optically multiplexing the first modulated data stream signal and the second unmodulated phase-synchronized coherence tone within an optical hub multiplexer, and communicating or transmitting the multiplexed data stream signal.multiplexed first modulated data stream signal and the second unmodulated phase-synchronized coherence tone to a first receiver via an optical fiber or optical fibers for downstream heterodyne or superposition detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features, aspects, and advantages of the present disclosure will be better understood when the following detailed description is read in relation to the accompanying drawings, in which similar symbols represent equal parts in the drawings, wherein: Fig. Figure 1 is a schematic representation of an exemplary fiber communication system according to an exemplary embodiment of the present disclosure. Fig. Figure 2 is a schematic representation showing an exemplary transmitter connected to the one in Fig. The fiber communication system shown in 1 can be used. Fig. Figure 3 is a schematic representation showing an alternative transmitter that is connected to the one in Fig. The fiber communication system shown in 1 can be used. Fig. Figure 4 is a schematic representation showing an alternative transmitter that is connected to the one in Fig. The fiber communication system shown in 1 can be used. Fig. Figure 5 is a schematic representation showing an alternative transmitter that is connected to the one in Fig. The fiber communication system shown in 1 can be used. Fig. Figure 6 is a schematic representation showing an exemplary upstream connection, which is connected to the one in Fig. The fiber communication system shown in 1 can be used. Fig. Figure 7 is a schematic representation showing an exemplary processing architecture that is used with the in Fig. The fiber communication system shown in section 1 was implemented. Fig. Figure 8 is a flowchart of an exemplary downstream optical network process. Fig. Figure 9 is a flowchart of an exemplary downstream optical network process, which is described in Fig. The downstream process shown in section 8 can be implemented.

[0015] Unless otherwise stated, the drawings provided herein are intended to illustrate the features of the embodiments of this disclosure. These features are presumably applicable to a multitude of systems, including one or more embodiments of this disclosure. Therefore, the drawings are not intended to include all conventional features known to those of ordinary craftsmanship or to the person skilled in the art that are necessary for carrying out the embodiments disclosed herein. DETAILED DESCRIPTION

[0016] In the following disclosure and the patent claims, reference is made to a number of terms which are defined as follows.

[0017] The singular forms “ein” (English a), “ein” (English an) and “der, die, das” (English the) also include plural forms or plural references, unless the context prescribes otherwise.

[0018] “Optional” means that the event or circumstance described below may or may not occur, and that the description includes cases in which the event occurs and cases in which it does not occur.

[0019] The approximation language or approximating formulations used herein throughout the disclosure and the claims may be used to modify any quantitative representation that could permissibly vary without altering the underlying function to which it refers. Accordingly, a value modified by one or more terms such as "over," "approximately," and "essentially" is not intended to be limited to the precisely stated value. In at least some cases, the approximation language may correspond to the accuracy of an instrument used to measure the value. Here, and throughout the disclosure and the claims, scope limitations may be combined and / or exchanged; these scopes are identified and include all subscopes contained therein unless context or language indicates otherwise.

[0020] Fig. Figure 1 is a schematic representation of an exemplary fiber communication system 100 according to an exemplary embodiment of the present disclosure. The system 100 comprises an optical hub 102, a fiber node 104, and an end user 106. The optical hub 102 is, for example, a central office, a communications hub, or an optical line terminal (OLT). In the illustrated embodiment, the fiber node 104 is shown for use with a passive optical network (PON). The end user 106 is a downstream termination unit, which may, for example, represent a customer device, customer premises (e.g., an apartment building), a business customer, or an optical network unit (ONU). In an exemplary embodiment, the system 100 uses a coherent dense wavelength division multiplexing (DWDM) PON architecture.

[0021] The optical hub 102 communicates with the fiber node 104 via a downstream fiber 108. Optionally, if upstream communication along the system 100 is desired, the optical hub 102 also connects to the fiber node 104 via the upstream fiber 110. In operation, the downstream fiber 108 and the upstream fiber 110 are typically 30 km or shorter. However, according to the embodiments presented herein, greater lengths are considered, such as between 100 km and 1000 km. In one exemplary embodiment, the fiber node 104 connects to the end user 106 via the fiber 112. Alternatively, the fiber node 104 and the end user 106 can be integrated as a single device, such as a virtualized cable modem termination system (vCMTS), which may be located in a customer room.If fiber node 104 and end user 106 are separate devices, the fiber optic cable 112 typically extends over a distance of about 5000 feet or less.

[0022] The optical hub 102 comprises an optical frequency comb generator 114, which is configured to receive a high-quality source signal 116 from an external laser 118 and thereby generate several coherence tones 120(1), 120(1'), 120(1'), ..., 120(N), 120(N'). The optical frequency comb generator 114 uses, for example, a mode-locked laser, a gain-switched laser, or electro-optic modulation and is designed to generate several coherence tones 120 as simultaneous low-linear wavelength channels with known and controllable spacing. This advantageous aspect of the upstream input signal to the system 100 enables a simplified architecture across the entire downstream part of the system 100, as described in more detail below.

[0023] Generated coherence tones 120 are fed into an amplifier 122, and the amplified signal from this amplifier is fed into a first optical hub demultiplexer 124. In an exemplary embodiment, the amplifier 122 is an erbium-doped fiber amplifier (EDFA). The optical hub 102 further comprises a downstream transmitter 126 and an optical hub multiplexer 128. In one embodiment, the optical hub 102 optionally comprises an optical hub splitter 130, an upstream receiver 132, and a second optical hub demultiplexer 134.

[0024] The downstream transmitter 126 comprises a downstream optical circulator 136 and a downstream modulator 138. In an exemplary embodiment, the downstream modulator 138 is an injection-locked laser modulator. The upstream receiver 132 comprises an upstream integrated coherence receiver (ICR) 140, an upstream analog-to-digital converter (ADC) 142, and an upstream digital signal processor (DSP) 144. In the exemplary embodiment, the fiber node 104 comprises an optical node demultiplexer 146. In an alternative embodiment where upstream transmission is desired, the fiber node 104 further comprises an optical node multiplexer 148. In the exemplary embodiment, the optical node demultiplexer 146 and the optical node multiplexer 148 are passive devices.

[0025] The end-user 106 further comprises a downstream receiver 150. In an exemplary embodiment, the downstream receiver 150 has a similar architecture to the upstream receiver 132 and comprises a downstream ICR 152, a downstream ADC 154, and a downstream DSP 156. For upstream transmission, the end-user 106 optionally comprises the end-user optical splitter 158, which may be located within the downstream receiver 150 or separately, and an upstream transmitter 160. In an exemplary embodiment, the upstream transmitter 160 has a similar architecture to the downstream transmitter 126 and comprises an upstream optical circulator 162 and an upstream modulator 164.

[0026] In operation, the system 100 uses the optical frequency comb generator 114 and the amplifier 122, which converts the incoming high-quality source signal 116 into several coherence tones 120 (e.g., 32 tones, 64 tones, etc.) that are then fed into the first optical hub demultiplexer 124. In an exemplary embodiment, the high-quality source signal 116 has sufficient amplitude and a narrow bandwidth such that a selected longitudinal mode of the signal 116 is transmitted to the optical frequency comb generator 114 without adjacent longitudinal modes, which are suppressed before processing by the comb generator 114. The first optical hub demultiplexer 124 then outputs a plurality of phase-synchronized coherence tone pairs 166(1), 166(2), ..., 166(N).That is, the generated coherent frequency tones 120 are amplified by the amplifier 122 to increase the optical power and then demultiplexed into several separate individual phase-synchronized coherence tone source pairs 166. For the sake of simplicity, the following description refers only to the coherence tone pair 166(1) corresponding to the synchronized pair signal for the first channel output, comprising a first unmodulated signal 168 for Ch1 and a second unmodulated signal 170 for Ch1', and their transmission or routing through the system 100.

[0027] The source signal 116, which is high-quality, narrowband, and essentially within a single longitudinal mode, outputs the coherence tone pair 166(1), comprising a first unmodulated signal 168 (Ch1) and a second unmodulated signal 170 (Ch1'), as a high-quality, narrowband signal. This signal then serves as the source for both seed and local oscillator (LO) signals for the downstream and upstream transmit and receive directions of the system 100. That is, the architecture of the optical frequency comb generator 114 advantageously produces high-quality continuous wave (CW) signals in an exemplary configuration. In particular, the first unmodulated signal 168 (Ch1) can act as a downstream seed and upstream LO in the entire system 100, while the second unmodulated signal 170 (Ch1') can simultaneously act as an upstream seed and downstream LO for the system 100.

[0028] According to the exemplary embodiment, within the optical hub 102, the first unmodulated signal 168 (Ch1) is split by the optical hub splitter 130 and fed separately into both the downstream transmitter 126 and the upstream receiver 132 as a "pure" signal, i.e., the essentially low-amplitude, continuous wave with a narrow bandwidth includes no appended data. The first unmodulated signal 168 (Ch1) thus becomes a seed signal for the downstream transmitter 126 and an LO signal for the upstream receiver 132. In an exemplary embodiment, within the downstream transmitter 126, the first unmodulated signal 168 (Ch1) passes through the downstream optical circulator 136 into the downstream modulator 138, in which one or more laser diodes (not in the Fig. 1 shown, subsequently in relation to the Fig. 2-5 described) are stimulated and data (also not in Fig. 1 shown, subsequently in relation to the Fig. 2-5 described) are added to the signal, which then leaves the downstream optical circulator 136 as a downstream modulated data stream 172 (Ch1).

[0029] In one exemplary embodiment, the downstream optical circulator 136 is located within the downstream transmitter 126. Alternatively, the downstream optical circulator 136 can be physically separate from the downstream transmitter 126 or located within the boundaries of the downstream modulator 138. The downstream modulated data stream 172 (Ch1) is then combined in the optical hub multiplexer 128 with the plurality of modulated / unmodulated data stream pairs from other channels (not shown) and transmitted via the downstream fiber 108 to an optical node demultiplexer 174 in the fiber node 104, which then separates the different channel stream pairs for transmission to different respective end users 106. Since the data stream pair 170, 172 entering the downstream receiver 150 at end user 106 is phase-synchronized, the digital signal processing at the downstream DSP 156 is greatly simplified, as shown below with regard to Fig. 7 is described.

[0030] If upstream reception is optionally sought or desired at the optical hub 102, the second unmodulated signal 170 (Ch1') within the end user 106 is split by the end user's optical spitter 158 and fed separately into both the downstream receiver 150 and the upstream transmitter 160 as a "pure" unmodulated signal for Ch1'. In this alternative embodiment, the second unmodulated signal 170 (Ch1') thus functions as a seed signal for the upstream transmitter 160 and as a "pseudo-LO signal" for the downstream receiver 150 for the coherent acquisition of Ch1. For the purposes of this discussion, the second unmodulated signal 170 (Ch1') is referred to as the "pseudo-LO signal" because it uses an LO signal from a remote source (output from the first optical hub demultiplexer 124) and is not needed to generate an LO signal locally at the end user 106.Furthermore, this special configuration significantly reduces the cost and complexity of the System 100 architecture by reducing the number of necessary electronic components.

[0031] For upstream transmission, in an exemplary embodiment, a similar coherent detection scheme is implemented for the upstream transmitter 160 as is used for the downstream transmitter 126. That is, the second unmodulated signal 170 (Ch1') is fed into the upstream optical circulator 162 and modulated by the upstream modulator 164 to produce symmetrical or asymmetrical data (not shown, as described below in relation to Fig. 6 described) using one or more slave lasers (also not shown, as below in relation to Fig. 6) to be added, and then output as an upstream-modulated data stream 176 (Ch1'), which is then combined with similar modulated data streams from other channels (not shown) by a node multiplexer 178 in fiber node 104. The second unmodulated signal 170 (Ch1') is then transmitted upstream over the upstream fiber 110, separated from other channel signals by the second optical hub demultiplexer 134, and fed into the upstream receiver 132 for simplified digital signal processing similar to the process described above with respect to the downstream receiver 150.

[0032] This exemplary configuration allows multiple upstream channels from different end users 106 to be multiplexed at fiber node 104 (or a remote node) and returned to optical hub 102. Thus, within optical hub 102, the same coherent detection scheme can be used at upstream receiver 132 as is used with downstream receiver 150, except that upstream receiver 132 uses the first unmodulated signal 168 (Ch1) as the LO and the upstream modulated data stream 176 (Ch1') to carry and transmit data, respectively, while downstream receiver 150 uses the data stream pair (Ch1, Ch1') in reverse. This means that the downstream receiver 150 uses the second unmodulated signal 170 (Ch1') as the LO and the downstream modulated data stream 172 (Ch1) to carry or transmit data.

[0033] The implementation of the embodiments described herein is useful for migrating from hybrid fiber-coaxial (HFC) architectures to other types of fiber architectures, as well as deeper fiber architectures. Typical HFC architectures usually have very few fiber strands from fiber nodes to the hub (e.g., fibers 108, 110), but many fiber strands could be used to cover the shorter distances typical for legacy or older HFC nodes to end users (e.g., fiber 112). In the exemplary embodiments described herein, two fibers (i.e., fibers 108, 110) are shown between the optical hub 102 and fiber node 104, which may be a legacy or older HFC fiber node. This means that one fiber (i.e., downstream fiber 108) is used for the downstream signal and the upstream seed / downstream LO, and another fiber (i.e., upstream fiber 110) is used for the upstream signal.Additionally, three fibers (i.e., fibers 112A-C) are shown for each end user, running from fiber node 104 (e.g., an old HFC fiber node) to end user 106. By using the advantageous configurations contained herein, fiber-deeper or fiber-migration schemes can utilize an HFC fiber node as a fiber distribution node, thereby greatly minimizing the need for fiber confinement from an HFC node to an optical hub.

[0034] The architecture described herein can therefore be structured as a significantly more cost-effective and compact physical device than conventional devices by avoiding the need for conventional compensation hardware. This novel and advantageous system and subsystem arrangement enables multi-wavelength emission with simplicity, reliability, and low cost. Furthermore, the implementation of the optical frequency comb generator 114 with the high-quality input source signal 116 allows for the simultaneous control of multiple sources, which cannot be achieved with conventional discrete lasers. According to the embodiments described herein, the channel spacing can be, for example, 25 GHz, 12.5 GHz, or 6.25 GHz, based on the available signal bandwidth.

[0035] The embodiments described herein realize further advantages through the use of a comb generator (i.e., the optical frequency comb generator 114) that maintains a constant wavelength spacing, thereby avoiding optical clock interference (OBI) that can occur in cases of simultaneous transmission over a single fiber. In the Fig. In the exemplary embodiment shown in Figure 1, the fiber node 104 is depicted as a passive system, which is expected to give it higher reliability than other migration approaches. Nevertheless, a person skilled in the art, after reading and understanding the present application, will understand how the embodiments disclosed herein can also be adapted to a remote PHY solution or a remote cable modem termination system (CMTS) contained within the fiber node.

[0036] As illustrated and described herein, the System 100 can utilize a coherent DWDM-PON architecture that incorporates novel solutions to meet the unique requirements of the access environment, yet with cost-effective structures not found in conventional hardware systems. The optical frequency comb generator 114 generates a multitude of simultaneously narrowband wavelength channels with controlled spacing, thus enabling simplified tuning of the entire wavelength comb. This centralized comb light source in the optical hub 102 therefore provides master seed sources and LO signals for the downstream and upstream directions in heterodyne and superimposed detection configurations, respectively, allowing the optical sources to be reused throughout the System 100's lifetime.This advantageous configuration enables significant cost savings and a reduction in hardware complexity compared to intradynamic detection methods, e.g. in long-range systems.

[0037] Fig. Figure 2 is a schematic representation showing an exemplary downstream transmitter 200, connected to the one in Fig. The fiber communication system 100 shown in Figure 1 can be used. The downstream transmitter 200 includes the downstream optical circulator 136 (see Figure 1). Fig. 1, above) in two-way communication with a laser-injected modulator 202, which includes a laser diode 204 that receives data 206 from an external data source 208. In an alternative embodiment, the downstream transmitter 200 can include two separate fiber receivers (not shown) which would replace and render redundant the downstream optical circulator 136 in the structural configuration shown.

[0038] In operation, the Downstream Transmitter 200 performs the same general functions as the Downstream Transmitter 126 ( Fig. 1, see above). The laser-injected modulator 202 uses the laser diode 204 as a “slave laser”. That is, the laser diode 204 is injection-locked by the external laser 118, which acts as a single-frequency or longitudinal-mode master or seed laser, to keep the frequency of a resonator mode of the laser diode 204 close enough to the frequency of the master laser (i.e., laser 118) to allow frequency coupling. The principle of the downstream transmitter 200 is also referred to as "laser cloning", in which a single high-quality master laser (i.e., laser 118) transmits a low-noise signal (i.e., source signal 116) with a narrow bandwidth, and a relatively inexpensive slave laser (e.g., laser diode 204) can be used throughout the system 100 to transmit data-modulated signals, such as the downstream-modulated data stream 172 (Ch1).In one exemplary embodiment, the laser diode 204 is a Fabry-Perot laser diode (FP LD) or a vertical cavity surface-emitting laser (VCSEL), in contrast to the significantly more expensive, conventionally used distributed feedback laser diodes (DFB LD). In an alternative embodiment, the laser diode 204 is an LED which, due to the use of the high-quality source signal 116, which is consistently used throughout the system 100, can operate as a sufficient slave laser source according to the embodiments described herein.

[0039] More precisely, the first unmodulated signal 168 (Ch1) exiting the optical hub splitter 130 is fed into the downstream optical circulator 136, which then excites the laser diode 204, i.e., the laser diode 204 emits light at a specific modulation rate. The laser-injected modulator 202 appends the data 206 to the excited Ch1 signal, and the resulting modulated Ch1 signal with the appended data is output by the downstream optical circulator 136 as a downstream modulated data stream 172 (Ch1).According to this exemplary embodiment, the first unmodulated signal 168 (Ch1) is fed into the downstream transmitter 126 as an unmodulated, low-amplitude, low-noise, narrow-bandwidth "pure" source and modulated by the laser diode 204, which is a high-amplitude, wide-bandwidth device. The resulting downstream-modulated data stream 172 (Ch1) is a high-amplitude, low-noise, narrow-bandwidth "pure" signal that can be transmitted throughout the entire system 100 without the need for any further conventional compensation means (hardware and programming). For example, suppression of neighboring longitudinal modes by the laser diode 204 is not required because the excitation source signal (i.e., the signal 168) is of such high quality and narrow bandwidth that the output downstream-modulated data stream 172 (Ch1) is only substantially amplified within the narrow bandwidth of the external laser 118. In the in . Fig. In the exemplary embodiment shown in Figure 2, the laser-injected modulator 202 implements direct modulation.

[0040] The optical injection interlock described herein thus improves the performance of the relatively inexpensive, multi-longitudinal slave laser source (i.e., laser diode 204) with respect to spectral bandwidth and noise characteristics. With respect to heterodynically coherent detection, incoming signals (upstream or downstream) can be combined with the LO or the pseudo-LO and brought to an intermediate frequency (IF) for electronic processing. According to this exemplary configuration, a portion of the optical power of the LO / pseudo-LO can also be used as a master / seed laser for the reverse transmission direction at both the optical hub 102 and the end user 106 (see below regarding…). Fig. 6) can be used so that a fully coherent system with a master seed and LO delivery from an optical hub can be achieved relatively cost-effectively compared to conventional systems.

[0041] Fig. Figure 3 is a schematic representation showing an alternative downstream transmitter 300, which is connected to the one in Fig. The fiber communication system 100 shown in Figure 1 can be used. The downstream transmitter 300 is similar to the downstream transmitter 200 ( Fig. 2), including the implementation of direct modulation, except that the downstream transmitter 300 alternatively uses polarization multiplexing to modulate the Ch1 signal into the downstream modulated data stream 172 (Ch1).

[0042] The downstream transmitter 300 includes the downstream optical circulator 136 (see Fig. 1, above) in two-way communication with a laser-injected modulator 302 comprising a polarization beam splitter (PBS) / polarization beam combiner or combiner (PBC) 304, which may be a single device. The laser-injected modulator 302 further comprises a first laser diode 306 configured to receive first data 308 from an external data source (not in Fig. 3 shown), and a second laser diode 310, which is configured to receive second data 312 from the same or a different external data source.

[0043] In operation, the Downstream Transmitter 300 is similar to the Downstream Transmitter 200 with regard to the implementation of direct modulation and master / slave laser injection interlocking. However, the Downstream Transmitter 300 alternatively implements dual polarization from the splitter section of the PBS / PBC 304, which splits the first unmodulated signal 168 (Ch1) into its x-polarization component P1 and y-polarization component P2, each of which separately excites the first laser diode 306 and the second laser diode 310. Similar to the Downstream Transmitter 200 ( Fig. 2) In the downstream transmitter 300, the first unmodulated signal 168 (Ch1) exiting the optical hub splitter 130 is fed into the downstream optical circulator 136, whose separate polarization components then excite the laser diodes 306 and 310 at the specified modulation rate. The laser-injected modulator 302 appends the data from the first and second data points 308 and 312 to the respective excited polarization components of the Ch1 signal, which are combined by the combination section of the PBS / PBC 304. The resulting modulated Ch1 signal with the appended data is output by a downstream optical circulator 136 as a downstream-modulated data stream 172 (Ch1).

[0044] In an exemplary embodiment, the polarized light components received by the first and second laser diodes 306 and 310 are orthogonal (90 degrees and / or non-interactive). This means that the first laser diode 306 and the second laser diode 310 are optimized as slave lasers to align or lock onto the same wavelength as the external laser 118 (master), but with perpendicular polarization directions. This configuration allows large data packets (e.g., first data 308 and second data 312) to be split and simultaneously transmitted via separate paths as a downstream-modulated data stream 172 (Ch1) before recombination. Alternatively, the first data 308 and the second data 312 can originate from two (or more) separate, independent, or unrelated sources. The orthogonal splitting prevents data distortion or interference between the polarized signal components.However, a person skilled in the art will appreciate that, according to the embodiment of . Fig. 3. The first unmodulated signal 168 (Ch1) can also be polarized at 60 degrees, using similar principles of amplitude and phase as well as wavelength division. The first unmodulated signal 168 (Ch1) can alternatively be multiplexed according to spiral or vortex polarization or orbital angular momentum. In addition, while the illustrated embodiment includes polarization multiplexing, space multiplexing and mode division multiplexing or mode multiplexing can alternatively be implemented.

[0045] According to this exemplary embodiment, the continuous master wave signal for Ch1, namely the first unmodulated signal 168, is received by the optical frequency comb generator 114 and split. The first part serves as the local oscillator (LO) for the upstream receiver 132, and the second part synchronizes two slave lasers (i.e., first laser diode 306 and second laser diode 310) using their respective x-polarization and y-polarization light components, such that both slave lasers oscillate according to the wavelength of the master laser (i.e., external laser 118). Data (i.e., first data 308 and second data 312) is directly modulated onto the two slave lasers. This injection interlock technique thus further enables frequency modulation (FM) of the noise spectrum from the master laser to the slave laser and is also capable of significant improvements in the suppression of FM noise / phase disturbances.-to achieve vibration and the reduction of the emission transmission width.

[0046] As described herein, the use of optical injection with a dual-polarization optical transmitter (i.e., a downstream transmitter 300) by direct modulation can advantageously utilize relatively inexpensive lasers to perform the functions of conventional lasers, which are considerably more expensive. According to this configuration of a dual-polarization optical transmitter by direct modulation of a semiconductor laser in conjunction with coherent detection, the present embodiments are particularly suitable for short-range applications due to their lower cost and architectural compactness. Similar advantages can be realized in long-range applications.

[0047] Fig. Figure 4 is a schematic representation showing an alternative downstream transmitter 400, which is connected to the one in Fig. The fiber communication system 100 shown in Figure 1 can be used. The downstream transmitter 400 is similar to the downstream transmitter 200 ( Fig. 2), except that the downstream transmitter 400 alternatively implements external modulation, as opposed to direct modulation, to modulate the Ch1 signal into the downstream-modulated data stream 172 (Ch1). The downstream transmitter 400 includes the downstream optical circulator 136 (see Fig. 1, above) and a laser-injected modulator 402. The downstream optical circulator 136 is in one-way direct communication with a separate external optical circulator 404, which may be contained within a laser-injected modulator 402 or separately. The laser-injected modulator 402 further comprises a laser diode 406, which receives the first unmodulated signal 168 (Ch1) with low amplitude and narrow bandwidth and outputs an excited optical signal 408 with high amplitude and narrow bandwidth back to the external optical circulator 404. The laser-injected modulator 402 further comprises an external modulation element 410, which receives data 412 from an external data source 414 and appends the data 412 to the optical signal 408, which is to be received unilaterally by the downstream optical circulator 136 and output as a downstream modulated data stream 172 (Ch1).

[0048] In this exemplary embodiment, the downstream transmitter 400 performs the same general functions as the downstream transmitter 126 ( Fig. 1, see above), but uses external modulation as an injection locking mechanism to lock or adjust the laser diode 406 to the wavelength of the master laser source (e.g., external laser 118). To implement external modulation, this embodiment controls the optical signal flow by essentially one-sided optical circulators (i.e., downstream optical circulators 136, external optical circulators 404). The external modulation element 410 can optionally include a demultiplex filter (not shown) as an integral component or separately along the signal path of the downstream modulated data stream 172 (Ch1) before input by the downstream receiver 150. In an exemplary embodiment, the external modulation element 410 is a monitor photodiode, and the injection locking is achieved via a rear laser facet.

[0049] Fig. Figure 5 is a schematic representation showing an alternative downstream transmitter 500, which is connected to the one in Fig. The fiber communication system 100 shown in Figure 1 can be used. The downstream transmitter 500 is similar to the downstream transmitter 300 ( Fig. 3), including the implementation of direct modulation and polarization multiplexing, except that the downstream transmitter 500 further implements quadrature amplitude modulation (QAM) to modulate the Ch1 signal into the downstream-modulated data stream 172 (Ch1). That is, additional external modulation elements per polarization branch ( Fig. 2, above) can be used to generate QAM signals.

[0050] The downstream transmitter 500 includes the downstream optical circulator 136 (see Fig. 1, above) in two-way communication with a laser-injected modulator 502, which includes a PBS / PBC 504 that can be a single device or two separate devices. Furthermore, all components of the laser-injected modulator 502 can themselves be separate devices or, alternatively, all be contained in a single photonic chip. The laser-injected modulator 502 further includes a first laser diode 506 configured to receive first data 508 from an external data source (not in Fig. 5 shown) to receive, a second laser diode 510 which is configured to receive second data 512 from the same or a different external data source, a third laser diode 514 which is configured to receive third data 516 from the same / different external data source, and a fourth laser diode 518 which is configured to receive fourth data 520 from the same / different external data source.

[0051] In operation, the downstream transmitter 500 implements dual polarization from the splitter section of the PBS / PBC 504, which splits the first unmodulated signal 168 (Ch1) into its x-polarization component (P1) and y-polarization component (P2). Each polarization component P1, P2 is then fed into the first unpolarized optical splitter / combinator 522 and the second unpolarized optical splitter / combinator 524, respectively. The first and second optical splitters / combinators 522, 524 then each further divide their respective polarization components P1, P2 into their I-signals 526, 528 and also into their Q-signals 530, 532. The generated I-signals 526, 528 then directly excite the laser diodes 506, 514. Before direct communication with the laser diodes 510, 518 or 518The generated Q signals 530, 532 first pass through first and second quadrature phase shift elements 534, 536, which each shift the Q signal by 45 degrees in each direction, so that the respective Q signal is offset by 90 degrees from its respective I signal when recombinated at splitters / combinators 522, 524.

[0052] The resulting modulated Ch1 signal with appended data is output by the downstream optical circulator 136 of the downstream transmitter 500 as a downstream modulated data stream 172 (Ch1) and as a polarized, multiplexed QAM signal. According to this exemplary embodiment, the use of a photonic integrated circuit enables direct modulated polarization of a multiplexed coherent system, but using significantly more cost-effective hardware configurations than conventional architectures. In one exemplary embodiment, the laser diodes 506, 510, 514, and 516 are PAM-4 modulated laser diodes capable of generating 16-QAM polarization multiplexed signals.

[0053] Fig. Figure 6 is a schematic representation showing an exemplary upstream transmitter 600, connected to the one in Fig. The fiber communication system 100 shown in section 1 can be used. In the section shown in Fig. In the embodiment shown in Figure 6, the upstream transmitter 600 is identical in structure and function to the downstream transmitter 300 ( Fig. 3) similarly. In particular, the upstream transmitter 600 includes the upstream optical circulator 162 (see Fig. 1, above) in two-way communication with a laser-injected modulator 602 (not separately in Fig. 6 shown), comprising a PBS / PBC 604, which may be a single device or separate devices. The laser-injected modulator 602 further comprises a first laser diode 606 configured to receive first data 608 from an external data source (not in Fig. 6 shown) to receive, and a second laser diode 610 configured to receive second data 612 from the same or a different external data source. Similar to the embodiments described above. Fig. 2-5 The downstream transmitter 600 can also eliminate for the upstream optical circulator 162 by using at least two separate fiber receivers (not shown).

[0054] The upstream transmitter 600 is therefore almost identical to the downstream transmitter 300 ( Fig. 3), except that the upstream transmitter 600 uses the second unmodulated signal 170 (Ch1') as the end-user seed source in the laser-injected modulator 602 to combine or append it with data (e.g., first data 608, second data 612) to generate an upstream-modulated data stream 176 (Ch1') to transmit upstream data signals to an upstream receiver (e.g., upstream receiver 132). In operation, the first laser diode 606 and the second laser diode 610 also function as slave lasers by means of injection interlocking to the master signal from the external laser 118. That is, symmetrical or asymmetrical data for Ch1' (e.g., first data 608, second data 612) are modulated onto the two slave lasers (i.e., first laser diode 606 and second laser diode 610) using polarization multiplexing, similar to the process that occurs with respect to the downstream transmitter 300 ( Fig. 3) was implemented in optical hub 102.

[0055] This example illustrates the upstream transmitter 600, which is based on the architecture of the downstream transmitter 300 ( Fig. 3) essentially mimics. Alternatively, the upstream transmitter 600 could adopt the architecture of one or more downstream transmitters 200 ( Fig. 2), 400 ( Fig. 4) or 500 ( Fig. 5) imitate equivalently without deviating from the scope of protection of the present disclosure. In addition, the upstream sender 600 may imitate any of the information contained in the Fig. The embodiments disclosed in 2-5 correspond to the specific architecture of the respective downstream transmitter used within the optical hub 102. By using a high-quality, low-noise, narrow-bandwidth external laser source 118, the master / slave laser relationship permeates the entire system 100 and the multitude of end users 106 who receive modulated / unmodulated signal pairs (which can be 32, 64, 128, or up to 256 from a single fiber pair, e.g., downstream fiber 108 and upstream fiber 110).

[0056] The significant cost savings according to the present embodiments can therefore best be realized by considering that up to 512 downstream transmitters (e.g., 126 downstream transmitters) are possible. Fig. 1) and upstream transmitters (e.g., upstream transmitter 160, Fig. 1) may be required to fully realize all available chattel or mobile pairs from a single optical hub 102. The present embodiments implement a significantly more cost-effective and less complex hardware architecture to take advantage of the benefits of implementing a high-quality external laser 118 without having to add expensive individual longitudinal-mode laser diodes or other compensation hardware required to suppress neighboring longitudinal modes from inexpensive lasers or the noise components they generate.

[0057] Fig. Figure 7 is a schematic representation showing an exemplary processing architecture for the upstream receiver 132, the downstream receiver 150, and the [unclear text]. Fig. The fiber communication system 100 shown can be implemented. The respective architectures of the upstream receiver 132 and the downstream receiver 150 are similar in form and function (see above regarding Fig. 1), except that the upstream receiver 132 receives a first data stream pair 700 for Ch1, Ch1', inversely to a second data stream pair 702, which is received by the downstream receiver 150. In other words, as described above, the first data stream pair 700 comprises the first unmodulated signal 168 (Ch1) as the LO and the upstream modulated data stream 176 (Ch1') for data transmission, while the second data stream pair 702 comprises the unmodulated signal 170 (Ch1') as the LO and the downstream modulated data stream 172 (Ch1) for data transmission.

[0058] The first and second data stream pairs 700 and 702 of the multiplexed phase-synchronized pairs are modulated / unmodulated optical signals, which are converted into analog electrical signals by ICR 140 and ICR 152, respectively. The respective analog signals are then converted into a digital domain by ADC 142 and ADC 154 for digital signal processing by DSP 144 and DSP 156. In an exemplary embodiment, the digital signal processing can be performed by a CMOS ASIC with a very large number of gate arrays. A conventional CMOS ASIC, for example, can utilize up to 70 million gates to process incoming digitized data streams. In conventional systems, modulated data streams for Ch1 and Ch1' are processed independently, requiring significant resources to compensate for frequency offset, drift, and digital down-compensation factors (e.g.,e^-jωt, where ω represents the frequency difference between the first unmodulated signal 168 and the upstream modulated data stream 176, and ω is kept constant for the coherence tone pair 166, which is extended throughout the system 100) to estimate.

[0059] According to the exemplary embodiments disclosed herein, the modulated and unmodulated signals of Ch1 and Ch1' are phase-synchronized such that the difference ω between the signal pair is always known and is phase-synchronized to maintain a constant relationship. In contrast, conventional systems require estimating the carrier phase to compensate for factors such as drift or shift, which, as explained above, requires significant processing resources. However, since, according to the present embodiments, Ch1 and Ch1' are synchronized with each other as the first and second data stream pairs 700 and 702, the offset or shift ω between the pairs 700 and 702 does not need to be estimated, as it can instead be easily derived by a simplified subtraction process in DSP 144 and DSP 156, since the signal pairs drift together by the same amount in a constant relationship.This advantageous configuration and process allows digital signal processing to be performed by a CMOS ASIC with up to one million gates, thereby significantly improving the processing speed of the respective DSP and / or reducing the number of physical chips required for processing (or similarly, the number of separate processing operations that can be performed by the same chip). Currently, the implementation of the embodiments described herein can improve downstream and upstream data transmission speeds by up to 5000 times compared to conventional systems.

[0060] Fig. Figure 8 is a flowchart of an exemplary downstream optical network process or procedure 800, which is described in Fig. The fiber communication system 100 shown in Figure 1 can be implemented. The process or procedure 800 begins at step 802. In step 802, coherence tone pairs 166 are generated and output by the optical frequency comb generator 114, the amplifier 122, and the first optical hub demultiplexer 124. Similar to the discussion above, for the sake of simplicity, the following discussion focuses on the specific coherence tone pair 166(1) for Ch1, Ch1'. The coherence tone pair 166 comprises the first unmodulated signal 168 (Ch1) and the second unmodulated signal 170 (Ch1'). Once the coherence tone pair 166 is generated, the process 800 continues from step 802 with steps 804 and 806, which can be executed jointly or simultaneously.

[0061] In step 804, the first unmodulated signal 168 (Ch1) is fed into an optical splitter, e.g. the optical splitter 130, Fig. 1, entered. In step 806, the second unmodulated signal 170 (Ch1') is sent to a multiplexer, e.g., an optical hub multiplexer 128. Fig. 1. transmitted. Referring back to step 804, the first unmodulated signal 168 (Ch1) is split to function both as the LO for upstream detection and as the seed for downstream data transmission. For upstream detection, step 804 continues with step 808, where the first unmodulated signal 168 (Ch1) is received by an upstream receiver, i.e., upstream receiver 132. Fig. 1. is received. For downstream data transmission, step 804 continues separately and simultaneously with step 810.

[0062] Step 810 is an optional step where polarization multiplexing is desired. In step 810, the first unmodulated signal 168 (Ch1) is split into its x and y component parts P1 and P2 (e.g., by PBS / PBC 304, Fig. 3 or PBS / PBC 504, Fig. 5) split for separate direct or external modulation. If polarization multiplexing is not used, process 800 skips step 810 and instead proceeds directly from step 804 to step 812. In step 812, the first unmodulated signal 168 (Ch1), or its polarized components if the optional step 810 is implemented, is split by direct (e.g., Fig. 2, Fig. 3, Fig. 5) or external (e.g. Fig. 4) Modulation is applied. Process 800 then proceeds from step 812 to step 814. Step 814 is an optional step that is implemented if the optional step 810 is also implemented for polarization multiplexing. In step 814, the x and y component portions P1 and P2 are recombined for output as a downstream modulated data stream 172 (Ch1) (e.g., by PBS / PBC 304). Fig. 3 or PBS / PBC 504, Fig. 5) If polarization multiplexing was not used, process 800 skips step 814 and instead proceeds directly from step 812 to step 816.

[0063] In step 816, the second unmodulated signal 170 (Ch1') and the downstream modulated data stream 172 (Ch1) are optically multiplexed, i.e. by the optical hub multiplexer 128, Fig. 1, as a phase-synchronized data stream pair (e.g. second data stream pair 702, Fig. 7) Process 800 then proceeds from step 816 to step 818, with the phase-synchronized data stream pair being transmitted over an optical fiber, i.e., a downstream fiber 108, Fig. 1. Process 800 then proceeds from step 818 to step 820, where the synchronized data stream pair is optically demultiplexed, e.g., by the optical node demultiplexer 174 in fiber node 104. Process 800 then proceeds from step 820 to step 822, where components of the demultiplexed data stream pair (e.g., the second unmodulated signal 170 (Ch1') as well as the downstream modulated data stream 172 (Ch1)) are received by a downstream receiver (e.g., downstream receiver 150). Fig. 1) for coherent heterodyne or superposition detection.

[0064] If an end user (e.g., end user 106) further includes an upstream transmission capability, process 800 also includes the optional steps 824 and 826. In step 824 and before the downstream reception in step 822, the second unmodulated signal 170 (Ch1') is optically split (e.g., by the end-user optical splitter 158). Fig. 1) and in step 826 additionally to an upstream sender of the end user (e.g. upstream sender 160, Fig. 1) as a seed signal for a modulator (e.g., modulator 164, Fig. 1) transferred for upstream data transmission, as below in relation to Fig. 9 explained in more detail.

[0065] Fig. Figure 9 is a flowchart of an exemplary upstream optical network process 900, which can optionally be combined with the one described in Fig. The fiber communication system 100 shown in Figure 1 can be implemented. Process 900 begins with the optional step 902. In step 902, polarization multiplexing is performed in the upstream transmitter (e.g., upstream transmitter 160). Fig. 1) is used, the second unmodulated signal 170 (Ch1') (from step 826, Fig. 8) into its x and y component parts (e.g. by PBS / PBC 604, Fig. 6) split for separate direct or external modulation. If polarization multiplexing is not used, step 902 is skipped and process 900 starts instead at step 904.

[0066] In step 904, the second unmodulated signal 170 (Ch1') or its polarized components, if the optional step 902 is implemented, is sent to the master source laser (e.g. external laser 118, Fig. 1) Injection-locked, as above in relation to the Fig. 1 and Fig. 6 described. Step 904 then proceeds to step 906, where the injection-locked signal is modulated by direct or external modulation. Process 900 then proceeds from step 906 to step 908. Step 908 is an optional step that is implemented if the optional step 902 is also implemented for polarization multiplexing. In step 908, the x and y components of the excited Ch1' signal are recombined (e.g., by PBS / PBC 604, Fig. 6) to be output as upstream-modulated data stream 176 (Ch1'). If polarization multiplexing was not used, process 900 skips step 908 and instead proceeds directly from step 906 to step 910.

[0067] In step 910, the upstream modulated data stream 176 (Ch1') is optically multiplexed, i.e., by the optical node multiplexer 178. Fig. 1, with other upstream data stream signals (not shown). Process 900 then proceeds from step 910 to step 912, with the upstream modulated data stream 176 (Ch1') being transmitted via an optical fiber, i.e., upstream fiber 110, Fig. 1. Process 900 then proceeds from step 912 to step 914, where the upstream modulated data stream 176 (Ch1') is optically demultiplexed, e.g., by a second optical hub demultiplexer 134, which separates the selected data stream from the other upstream data stream signals, for transmission to a specific upstream receiver tuned to receive the modulated data stream. Process 900 then proceeds from step 914 to step 916, where both components (e.g., the first unmodulated signal 168 (Ch1), Fig. 8, as well as the upstream modulated data stream 176 (Ch1')) of the upstream data stream pair, e.g. the first data stream pair 700, Fig. 7, from an upstream receiver (e.g., upstream receiver and 32, Fig. 1) for coherent heterodyne or superposition detection.

[0068] As illustrated in the exemplary embodiment, one difference between upstream and downstream signal transmission is that a complete synchronized modulated / unmodulated channel pair (e.g., second data stream pair 702, Fig. 7) can be transmitted in the downstream direction, while in the upstream direction only a data-modulated signal (e.g., upstream-modulated data stream 176 (Ch1')) can be transmitted via the upstream fiber connection, i.e., upstream fiber 110. One advantage of the present configuration is that the LO can be used for upstream coherent detection (e.g., at the upstream receiver 132, Fig. 1) directly from the split signal, i.e., the first unmodulated signal 168 (Ch1) generated by the optical frequency comb generator 114 within the optical hub 102 after separation by the first optical hub demultiplexer 124, as in Fig. As shown in Figure 1, a laser source is generated. Conventional systems typically require LO generation at each stage of the respective system. According to the present disclosure, on the other hand, relatively inexpensive slave lasers can be implemented throughout the system architecture for modulation and polarization multiplexing in both optical hub 102 and end-user 106 components without requiring an additional LO source at the end user.

[0069] According to the present disclosure, the use of optical dual-polarization transmitters and direct modulation of semiconductor lasers with coherent detection is particularly advantageous not only for long-range applications but also for short-range applications, reducing the cost of electronic hardware while also enabling a more compact overall network system architecture. Furthermore, the presented systems and methods solve the conventional problem of synchronizing two laser sources over extended periods. The use of the included phase-synchronized data stream pairs and slave lasers enables continuous synchronization of the various laser sources throughout the entire system during operation. These solutions can be implemented cost-effectively within coherent DWDM-PON system architectures for access networks.

[0070] The use of the high-quality optical comb source at the front end of the system thus enables the generation of a large number of simultaneous narrow-bandwidth wavelength channels with easily controllable spacing, thereby simplifying the tuning of the entire wavelength comb. This centralized comb light source in the optical hub provides master seed sources and LO signals that can be reused throughout the system for both downstream and upstream transmission. Furthermore, the implementation of optical injection, as described here, improves the performance of cost-effective multi-longitudinal slave laser sources in terms of spectral bandwidth and noise characteristics.Access networks according to current systems and methods thus achieve a more efficient transmission of wavelengths through fiber optics, thereby increasing the capacity of the transmitted data, but with lower power, increased sensitivity, lower hardware costs and a reduction in dispersion, DSP compensation and error correction.

[0071] Exemplary embodiments of fiber communication systems and methods are described in detail above. However, the systems and methods of this disclosure are not limited to the specific embodiments described here; rather, the components and / or steps of their implementation can be used independently and separately from other components and / or steps described here. Additionally, the exemplary embodiments can be implemented and used in conjunction with other access networks using fiber and coaxial transmission at the end-user level.

[0072] This written description uses examples to disclose embodiments, including the best mode, and to enable any person skilled in the art to carry out or apply these embodiments, including the manufacture and use of devices or systems and the performance of integrated processes. The patentable scope of the disclosure is defined by the claims and may include other examples that would occur to a person skilled in the art. Such other examples shall fall within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they have equivalent structural elements with insignificant differences from the literal language of the claims.

[0073] Although specific features of different embodiments of the disclosure may be shown in some drawings and not in others, this is for clarity only. According to the principles of the disclosure, a particular feature shown in one drawing may be referenced and / or claimed in combination with features of the other drawings. For example, the following list of exemplary claims represents only a portion of the possible combinations of elements that are possible from the systems and methods described herein. a(i). Injection-locked transmitter for an optical communications network comprising: a master-seed laser source input substantially restricted to a single longitudinal mode; an input data stream; and a laser-injected modulator comprising at least one slave laser having a resonator frequency injection-locked to a frequency of the single longitudinal mode of the master-seed laser source, wherein the laser-injected modulator is configured to receive the master-seed laser source input and the input data stream and to output a laser-modulated data stream. b(i). Transmitter according to claim a(i), wherein the laser-injected modulator is configured to implement direct modulation. c(i). Transmitter according to claim a(i), wherein the laser-injected modulator is configured to implement an external modulation. d(i). Transmitter according to claim a(i), wherein the at least one slave laser comprises at least one of an LED, a Fabry-Perot laser diode and a surface-emitting laser with a vertical resonator. e(i). Transmitter according to claim a(i), further comprising a first optical circulator in communication with the laser-injected modulator and the master-seed laser source input. f(i). Transmitter according to claim e(i), wherein the laser-injected modulator is configured to implement one of polarization multiplexes, space multiplexes and mode multiplexes. g(i). Transmitter according to claim f(i), wherein the laser-injected modulator is configured to multiplex the master-seed laser source input at a polarization of 90 degrees, 60 degrees, 90 degrees, spiral polarization, circular polarization, vortex polarization or orbital angular momentum. h(i). Transmitter according to claim f(i), further comprising a polarization beam splitter and a polarization beam combiner arranged between the first optical circulator and the at least one slave laser. i(i). Transmitter according to claim h(i), wherein the at least one slave laser comprises a first laser diode and a second laser diode, wherein the first laser diode is configured to receive an x-component of the master seed laser source input, and wherein the second laser diode is configured to receive a y-component of the master seed laser source input. j(i). The transmitter according to claim i(i), further comprising: a first optical splitter and optical combiner arranged between the polarization beam splitter and the first laser diode; and a second optical splitter and optical combiner arranged between the polarization beam splitter and the second laser diode, wherein the first laser diode comprises a first sub-laser and a second sub-laser, wherein the second laser diode comprises a third sub-laser and a fourth sub-laser, wherein the first sub-laser is configured to receive an I-signal of the x-component, wherein the second sub-laser is configured to receive a Q-signal of the x-component, wherein the third sub-laser is configured to receive an I-signal of the y-component, and wherein the fourth sub-laser is configured to receive a Q-signal of the y-component. k(i). Transmitter according to claim j(i), further comprising: a first phase-shifting element arranged between the first optical splitter and the second sublaser; and a second phase-shifting element arranged between the second optical splitter and the fourth sublaser. l(i). Transmitter according to claim e(i), further comprising: a second optical circulator in one-way communication with the first optical circulator and in two-way communication with the at least one slave laser; and an external modulation element arranged between the first optical circulator and the second optical circulator, wherein the external modulation element is configured to receive the input data stream and an output of the second optical circulator, wherein the first optical circulator is in one-way communication with an output of the external modulation element. a(ii) An optical network communication system comprising: an input signal source; an optical frequency comb generator configured to receive the input signal source and output a plurality of phase-synchronized coherence tone pairs, each of the plurality of phase-synchronized coherence tone pairs comprising a first unmodulated signal and a second unmodulated signal; a first transmitter configured to receive the first unmodulated signal of a selected pair of phase-synchronized coherence tone pairs as a seed source and to output a first modulated data stream; and a first receiver configured to receive the first modulated data stream from the first transmitter and to receive the second unmodulated signal of the selected pair of phase-synchronized coherence tone pairs as a local oscillator source. b(ii). System according to claim a(ii), wherein the optical frequency comb generator comprises an amplifier and an optical demultiplexer. c(ii). System according to claim a(ii), wherein the optical frequency comb generator is configured to implement a mode-locked laser, a gain-switched laser and an electro-optic modulation. d(ii). System according to claim a(ii), wherein the selected tone pair from the plurality of phase-synchronized coherence tone pairs can be controlled at a constant frequency interval to each other throughout the entire system. e(ii). System according to claim a(ii), wherein the system is configured to perform heterodyne or superposition detection. f(ii). System according to claim a(ii), wherein the first transmitter comprises a first laser-injected modulator and a first optical circulator. g(ii). System according to claim a(ii), wherein the first laser-injected modulator is configured to implement direct modulation. h(ii). System according to claim a(ii), wherein the first laser-injected modulator is configured to implement an external modulation. i(ii). System according to claim g(ii), wherein the input signal source comprises an external master laser. j(ii). System according to claim i(ii), wherein the first modulator comprises a first laser diode configured to activate the injection interlock for the external master laser. k(ii). System according to claim j(ii), wherein the first laser diode is configured to receive first data from a first external data source in order to append it to the output first modulated data stream. l(ii). System according to claim j(ii), wherein the first modulator further comprises a first polarization beam splitter and a first polarization beam combiner. m(ii). System according to claim l(ii), wherein the first laser diode comprises first and second slave lasers, wherein the first and second slave lasers are configured to receive first and second polarization components from the first polarization beam splitter. n(ii). System according to claim m(ii), wherein the first modulator is configured to implement quadrature amplitude modulation. o(ii). System according to claim n(ii), wherein the first slave laser comprises a first sub-laser and a second sub-laser, wherein the second slave laser comprises a third sub-laser and a fourth sub-laser, wherein the first and second sub-lasers are each configured to receive an I-signal and a Q-signal of the first polarization component, and wherein the third and fourth sub-lasers are each configured to receive an I-signal and a Q-signal of the second polarization component. p(ii). System according to claim a(ii), further comprising a second transmitter configured to receive the second unmodulated signal of one selected from the plurality of phase-synchronized coherence tone pairs as a seed source and to output a second modulated data stream. q(ii). System according to claim p(ii), wherein the second transmitter is configured to implement direct and external modulation. r(ii). System according to claim p(ii), wherein the second transmitter is configured to implement one or more polarization multiplexing and quadrature amplitude modulation. s(ii). System according to claim p(ii), further comprising a second receiver configured to receive the second modulated data stream from the second transmitter and to receive the first unmodulated signal of one selected from the plurality of phase-synchronized coherence tone pairs as a local oscillator source. a(iii) Optical network communication system comprising: an optical hub with an optical frequency comb generator configured to output at least one phase-synchronized coherence tone pair with a first unmodulated signal and a second unmodulated signal, and a downstream transmitter configured to receive the first unmodulated signal as a seed source and to output a downstream modulated data stream; a fiber node; and an end user with a downstream receiver configured to receive the downstream modulated data stream from the downstream transmitter and to receive the second unmodulated signal as a local oscillator source. b(iii). System according to claim a(iii), wherein one selected from the plurality of phase-synchronized coherence tone pairs is controllable in the entire system at a constant frequency distance to each other. c(iii). System according to claim a(iii), wherein the optical hub further comprises an amplifier, a first optical hub demultiplexer and an optical hub multiplexer. d(iii). System according to claim c(iii), wherein the fiber node comprises an optical node demultiplexer configured to demultiplex an output of the optical hub multiplexer. e(iii). System according to claim d(iii), wherein the optical hub multiplexer is configured to communicate with the optical node demultiplexer via a downstream fiber. f(iii). System according to claim d(iii), wherein the optical node demultiplexer is configured to communicate with the downstream transmitter via first optical fibers. g(iii). System according to claim a(iii), wherein the downstream receiver comprises a downstream integrated coherent receiver, a downstream analog-to-digital converter and a downstream digital signal processor. h(iii). System according to claim f(iii), wherein the end user further comprises an upstream transmitter, wherein the fiber node further comprises an optical node multiplexer, and wherein the optical hub further comprises a second optical hub demultiplexer and an upstream receiver. i(iii). System according to claim h(iii), wherein the upstream transmitter is configured to communicate with the optical node multiplexer via second optical fibers, and wherein the optical node multiplexer is configured to communicate with the second optical hub demultiplexer via an upstream fiber. j(iii). System according to claim i(iii), wherein the upstream transmitter is configured to receive the second unmodulated signal as a seed source and to output an upstream modulated data stream to the optical node multiplexer. k(iii). System according to claim i(iii), wherein the upstream receiver comprises an upstream integrated coherent receiver, an upstream analog-to-digital converter and an upstream digital signal processor. l(iii). System according to claim i(iii), wherein the upstream receiver is configured to receive the upstream modulated data stream from the optical node multiplexer as a data source and to receive the first unmodulated signal from the first optical hub demultiplexer as a local oscillator source. m(iii). System according to claim a(iii), wherein the at least one phase-synchronized coherence tone pair is controllable at a constant frequency distance to each other throughout the entire system. n(iii). System according to claim a(iii), wherein the end user comprises at least one customer device, customer premises, a business user and an optical network unit. o(iii). System according to claim a(iii), further configured to implement a coherent, dense, wavelength-division multiplexed passive optical network architecture. p(iii). System according to claim i(iii), wherein the downstream digital signal processor is configured to keep the difference in the frequency separation ω between the second unmodulated signal and the downstream modulated data stream constant when a digital downconversion compensation factor e^-jωt is calculated. q(iii). System according to claim k(iii), wherein the upstream digital signal processor is configured to keep the difference in the frequency separation ω between the first unmodulated signal and the upstream modulated data stream constant when the digital downconversion compensation factor e^-jωt is calculated. a(iv). A network processing method comprising the steps of: generating at least one pair of first and second unmodulated phase-synchronized coherence tones; transmitting the first unmodulated phase-synchronized coherence tone to a first sender as a seed signal; appending downstream data in the first sender to the first unmodulated phase-synchronized coherence tone to generate a first modulated data stream signal; optically multiplexing the first modulated data stream signal and the second unmodulated phase-synchronized coherence tone together within an optical hub multiplexer; and transmitting or communicating the multiplexed first modulated data stream signal and the second unmodulated phase-synchronized coherence tone to a first receiver via an optical fiber or fibers for downstream heterodyne or superposition detection. b(iv). Method according to claim a(iv), further comprising the step of polarization beam splitting of the first unmodulated phase-synchronized coherence tone prior to the step of adding downstream data. c(iv). Method according to claim b(iv), further comprising, after the step of adding downstream data and before the step of optical multiplexing, the step of combining polarization beams of split components from the step of polarization beam splitting of the first unmodulated phase-synchronized coherence tone. d(iv). Method according to claim a(iv), wherein the step of appending downstream data implements an injection interlock. e(iv). Method according to claim a(iv), further comprising the steps: optically splitting the second unmodulated phase-synchronized coherence tone prior to the communicating step; and receiving a portion of the optically split second unmodulated phase-synchronized coherence tone as a local oscillator for upstream detection by a second transmitter. f(iv). Method according to claim e(iv), further comprising a step of appending upstream data in the second transmitter to the second unmodulated phase-synchronized coherence tone to generate a second modulated data stream signal. g(iv). Method according to claim f(iv), wherein the step of appending upstream data comprises a step of injection locking of a slave laser to an external master laser. h(iv). Method according to claim f(iv), further comprising, prior to the step of adding upstream data, the step of polarization beam splitting of the second unmodulated phase-synchronized coherence tone. i(iv). Method according to claim h(iv), further comprising, after the step of adding upstream data, the step of combining polarization beams of split components from the step of splitting the polarization beam of the second unmodulated phase-synchronized coherence tone. j(iv). Method according to claim f(iv), further comprising a step of transmitting the second modulated data stream signal to a second receiver via an optical fiber or optical fibers for upstream heterodyne or superposition detection.

[0074] Some embodiments involve the use of one or more electronic or computer-based devices. Such devices typically include a processor or controller, such as a central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an application-specific integrated circuit (ASIC), a programmable logic circuit (PLC), a field-programmable gate array (FPGA), a digital signal processor (DSP), and / or any other circuit or processor capable of performing the functions described herein. The processes or procedures described herein may be encoded as executable instructions contained on a computer-readable medium, including, but not limited to, a storage device.storage device) and / or a memory device. Such instructions, when executed by a processor, cause the processor to perform at least some of the procedures described herein. The above examples are merely illustrative and are therefore not intended to limit the definition and / or meaning of the term "processor" in any way.

Claims

[1] Injection-locked transmitter for an optical communications network comprising: a master seed laser source input that is limited to a single longitudinal mode; an input data stream; and a laser-injected modulator comprising at least one slave laser with a resonator frequency locked to a frequency of the single longitudinal mode of the master-seed laser source, wherein the laser-injected modulator is configured to receive the master-seed laser source input and the input data stream and to output a laser-modulated data stream, characterized by , that the sender further includes: a first optical circulator in communication with the laser-injected modulator and the master-seed laser source input; a second optical circulator in one-way communication with the first optical circulator and in two-way communication with the at least one slave laser; and an external modulation element located between the first optical circulator and the second optical circulator, wherein the external modulation element is configured to receive the input data stream and an output from the second optical circulator, where the first optical circulator is in one-way communication with an output of the external modulation element. [2] Transmitter according to claim 1, wherein the laser-injected modulator is configured to implement direct modulation. [3] Transmitter according to claim 1, wherein the laser-injected modulator is configured to implement external modulation. [4] Transmitter according to one of the preceding claims, wherein the at least one slave laser comprises at least one LED, a Fabry-Perot laser diode and a surface-emitting laser with a vertical resonator. [5] Transmitter according to one of the preceding claims, wherein the laser-injected modulator is configured to implement one of polarization division multiplexing, space division multiplexing and mode division multiplexing. [6] Transmitter according to claim 5, wherein the laser-injected modulator is configured to multiplex the master seed laser source input at a 90-degree polarization, a 60-degree polarization, a 90-degree polarization, a spiral polarization, a circular polarization, a vortex polarization or an orbital angular momentum. [7] Transmitter according to claim 5 or 6, further comprising a polarization beam splitter and a polarization beam combiner arranged between the first optical circulator and the at least one slave laser. [8] Transmitter according to claim 7, wherein the at least one slave laser comprises a first laser diode and a second laser diode, wherein the first laser diode is configured to receive an x-component of the master seed laser source input, and the second laser diode is configured to receive a y-component of the master seed laser source input. [9] Transmitter according to claim 8, further comprising: a first optical splitter and optical combiner arranged between the polarization beam splitter and the first laser diode; and a second optical splitter and optical combiner arranged between the polarization beam splitter and the second laser diode, wherein the first laser diode comprises a first sublaser and a second sublaser, wherein the second laser diode comprises a third sublaser and a fourth sublaser, where the first sublaser is set up to receive an I-signal of the x-component, the second sublaser is configured to receive a Q signal of the x component, the third sublaser is configured to receive an I-signal from the Y-component, the fourth sublaser is set up to receive a Q signal of the y component. [10] Transmitter according to claim 9, further comprising: a first phase-shifting element located between the first optical splitter and the second sublaser; and a second phase-shifting element located between the second optical splitter and the fourth sublaser. [11] Optical network communication system, which includes: an input signal source; an optical frequency comb generator configured to receive the input signal source and output a plurality of phase-synchronized coherence tone pairs, each of the plurality of phase-synchronized coherence tone pairs comprising a first unmodulated signal and a second unmodulated signal, a first transmitter configured to receive the first unmodulated signal of a selected pair of phase-synchronized coherence tone pairs as a seed source and to output a first modulated data stream; and a first receiver configured to receive the first modulated data stream from the first transmitter and to receive the second unmodulated signal of one selected from the multitude of phase-synchronized coherence tone pairs as a local oscillator source, where one selected tone from the multitude of phase-synchronized coherence tone pairs can be controlled within the entire system at a constant frequency interval from each other. [12] System according to claim 11, wherein the optical frequency comb generator comprises an amplifier and an optical demultiplexer. [13] System according to claim 11 or 12, wherein the optical frequency comb generator is configured to implement a mode-locked laser, a gain-switched laser and an electro-optic modulation. [14] System according to any one of claims 11 to 13, wherein the system is configured to perform heterodyne detection. [15] System according to any one of claims 11 to 14, wherein the first transmitter comprises a first laser-injected modulator and a first optical circulator. [16] System according to any one of claims 11 to 15, wherein the first laser-injected modulator is configured to implement direct modulation. [17] System according to any one of claims 11 to 15, wherein the first laser-injected modulator is configured to implement an external modulation. [18] System according to one of claims 16 or 17, wherein the input signal source comprises an external master laser. [19] System according to claim 18, wherein the first modulator comprises a first laser diode configured to inject the external master laser. [20] System according to claim 19, wherein the first laser diode is configured to receive first data from a first external data source in order to append it to the output of the first modulated data stream. [21] System according to claim 19 or 20, wherein the first modulator further comprises a first polarization beam splitter and a first polarization beam combiner. [22] System according to claim 21, wherein the first laser diode comprises first and second slave lasers, wherein the first and second slave lasers are configured to receive first and second polarization components from the first polarization beam splitter. [23] System according to claim 22, wherein the first modulator is configured to implement quadrature amplitude modulation. [24] System according to claim 23, wherein the first slave laser comprises a first sub-laser and a second sub-laser, wherein the second slave laser comprises a third sub-laser and a fourth sub-laser, wherein the first and second sublasers are each configured to receive an I-signal or a Q-signal of the first polarization component, and the third and fourth sublasers are each configured to receive an I-signal or a Q-signal of the second polarization component. [25] System according to one of claims 11 to 24, further comprising a second transmitter configured to receive the second unmodulated signal of one selected from the plurality of phase-synchronized coherence tone pairs as a seed source and to output a second modulated data stream. [26] System according to claim 25, wherein the second transmitter is configured to implement one of direct and external modulation. [27] System according to claim 25 or 26, wherein the second transmitter is configured to implement one or more polarization division multiplexing and quadrature amplitude modulation(s). [28] System according to one of claims 25 to 27, further comprising a second receiver configured to receive the second modulated data stream from the second transmitter and to receive the first unmodulated signal of one selected from the plurality of phase-synchronized coherence tone pairs as a local oscillator source. [29] Optical network communication system, which includes: an optical hub with an optical frequency comb generator, with a downstream transmitter and an optical hub multiplexer, wherein the frequency comb generator is configured to output at least one phase-synchronized coherence tone pair with a first unmodulated signal and a second unmodulated signal, wherein the downstream transmitter is configured to receive the first unmodulated signal as a seed source and to output a downstream modulated data stream, wherein the downstream transmitter is further configured to perform a polarization beam split of the first unmodulated phase-synchronized coherence tone prior to appending downstream data and to append downstream data to the first unmodulated phase-synchronized coherence tone to generate the downstream modulated data stream, wherein the optical hub multiplexer is configured to optically multiplex the first modulated data stream signal and the second unmodulated phase-synchronized coherence tone together; a fiber knot; and an end user comprising a downstream receiver configured to receive the downstream modulated data stream from the downstream transmitter and to receive the second unmodulated signal as a local oscillator source. [30] System according to claim 29, wherein one selected from the plurality of phase-synchronized coherence tone pairs can be controlled in the entire system at a constant frequency interval to each other. [31] System according to claim 29 or 30, wherein the optical hub further comprises an amplifier and a first optical hub demultiplexer. [32] System according to claim 31, wherein the fiber node comprises an optical node demultiplexer configured to demultiplex an output of the optical hub multiplexer. [33] System according to claim 32, wherein the optical hub multiplexer is configured to communicate with the optical node demultiplexer via a downstream fiber. [34] System according to claim 32 or 33, wherein the optical node demultiplexer is configured to communicate with the downstream transmitter via first optical fibers. [35] System according to any one of claims 29 to 34, wherein the downstream receiver comprises a downstream integrated coherent receiver, a downstream analog-to-digital converter and a downstream digital signal processor. [36] System according to claim 34 or 35, where the end user further includes an upstream sender, wherein the fiber node further comprises an optical node multiplexer, and the optical hub further comprises a second optical hub demultiplexer and an upstream receiver. [37] System according to claim 36, wherein the upstream transmitter is configured to communicate with the optical node multiplexer via second optical fibers, and the optical node multiplexer is configured to communicate with the second optical hub demultiplexer via an upstream fiber. [38] System according to claim 37, wherein the upstream transmitter is configured to receive the second unmodulated signal as a seed source and to output an upstream modulated data stream to the optical node multiplexer. [39] System according to claim 37 or 38, wherein the upstream receiver comprises an upstream integrated coherent receiver, an upstream analog-to-digital converter and an upstream digital signal processor. [40] System according to one of claims 37 to 39, wherein the upstream receiver is configured to receive the upstream modulated data stream from the optical node multiplexer as a data source and to receive the first unmodulated signal from the first optical hub demultiplexer as a local oscillator source. [41] System according to one of claims 29 to 40, wherein the at least one phase-synchronized coherence tone pair is controllable at a constant frequency distance to each other throughout the entire system. [42] System according to any one of claims 29 to 41, wherein the end user comprises at least one customer device, customer premises, a business user and an optical network unit. [43] System according to any one of claims 29 to 42, further configured to implement a coherent, dense, wavelength-division multiplexed passive optical network architecture. [44] System according to any one of claims 37 to 43, wherein the downstream digital signal processor is configured to keep the difference in frequency separation ω between the second unmodulated signal and the downstream modulated data stream constant when a digital downconversion compensation factor e^-jωt is calculated. [45] System according to any one of claims 39 to 44, wherein the upstream digital signal processor is configured to keep the difference in frequency separation ω between the first unmodulated signal and the upstream modulated data stream constant when the digital downconversion compensation factor e^-jωt is calculated. [46] Methods for optical network processing, comprising the steps: Generating at least one pair of first and second unmodulated phase-synchronized coherence tones; Transmission of the first unmodulated phase-synchronized coherence tone to a first transmitter as a seed signal; Polarization beam splitting of the first unmodulated phase-synchronized coherence tone before the appending of downstream data; Appending downstream data in the first transmitter to the first unmodulated phase-synchronized coherence tone to generate a first modulated data stream signal; Optical multiplexing of the first modulated data stream signal and the second unmodulated phase-synchronized coherence tone together in an optical hub multiplexer; and Communicating the multiplexed first modulated data stream signal and the second unmodulated phase-synchronized coherence tone to a first receiver via fiber optic cable for downstream heterodyne detection. [47] The method of claim 46, further comprising, after the step of adding downstream data and before the step of optical multiplexing, the step of polarization beam combining split components from the polarization beam splitting step of the first unmodulated phase-synchronized coherence tone. [48] ​​Method according to claim 46 or 47, wherein the step of appending downstream data implements injection locking. [49] Method according to any one of claims 46 to 48, further comprising the steps: optical splitting of the second unmodulated phase-synchronized coherence tone prior to the communication step; and Receiving part of the optically split second unmodulated phase-synchronized coherence tone as a local oscillator for upstream detection by a second transmitter. [50] Method according to claim 49, further comprising a step of appending upstream data in the second transmitter to the second unmodulated phase-synchronized coherence tone to generate a second modulated data stream signal. [51] Method according to claim 50, wherein the step of adding upstream data comprises a step of injection locking of a slave laser to an external master laser. [52] Method according to claim 50 or 51, further comprising, prior to the step of adding upstream data, the step of polarization beam splitting of the second unmodulated phase-synchronized coherence tone. [53] The method of claim 52, further comprising, after the step of adding upstream data, the step of combining polarization beams of split components from the step of splitting the polarization beam of the second unmodulated phase-synchronized coherence tone. [54] Method according to one of claims 50 to 53, further comprising a step of transmitting the second modulated data stream signal to a second receiver by means of fiber optic cable for upstream heterodyne detection.

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