Colorless Optical Network Unit Research Articles

Scheme for a WDM-PON with colorless optical network units based on a flat optical frequency comb.

A new, to the best of our knowledge, scheme for a wavelength division multiplexing passive optical network (WDM-PON) based on a flat optical frequency comb (OFC) is proposed. Using an OFC as the optical source of the system can realize the colorlessness of optical network units (ONUs), and the direct detection of the downlink data further simplifies the ONU structure. The coherent demodulation of the uplink data improves the system performance due to the coherence of the comb lines. In this research, the proposed system is studied for its performance and power budgeting. The results show the flexibility, effectiveness, and practicability of the proposed scheme, which can be applied to future high-capacity optical access networks.

Design of Broadband Passive Optical Network Incorporating Different Modulation Formats and Colorless ONUs

In this work, a bidirectional broadband passive optical network (BPON) is proposed at 622.08 Mbps by incorporating colorless optical network units and different pulse shapes such as Duo-binary return to zero (DRZ), return to zero (RZ) and non-return to zero (NRZ). For varied link lengths, launching powers in terms of log BER, and Quality factor for downstream and upstream, the design of BPON is examined. The duo-binary advanced pulse shape outperformed the others in bidirectional BPON, achieving a symmetrical distance of 25 kilometres.

Heterogeneous Optical Access Networks: Enabling Low-Latency 5G Services With a Silicon Photonic Smart Edge

In the 5G era, optical fronthaul is a major challenge in meeting growing demand. Edge computation and coordinated multipoint for 5G have stringent requirements for high throughput and low latency, either in single-wavelength or wavelength-division-multiplexing fronthaul. We propose a new silicon photonic solution to deliver 5G services on existing optical access networks with colorless optical network units, such as passive optical networks. The newly added 5G services form a heterogeneous optical access network. Using the existing fiber infrastructure, broadband services coexist with new 5G signals that can densify 5G coverage. The proposed scheme is both wavelength-selective (in the distribution network) and colorless (at the end user site). We use silicon microring modulators to create subcarriers slaved from the broadband service distributed carrier; additional microring modulators generate 5G signals exploiting those subcarriers. We experimentally validated the successful coexistence of 5G signals (various formats) with a broadband signal (various formats).

Horn-Waveguide RSOA-EAM as a Colorless Emitting Source With Reduced Crosstalk

We proposed, designed, and fabricated a monolithically integrated horn-waveguide asymmetric reflective semiconductor optical amplifier electro-absorption modulator (RSOA-EAM) to discriminately process down- and up-stream signals for colorless optical network units in the wavelength-division multiplexing passive optical network (PON). It is demonstrated that the horn-waveguide RSOA-EAM can effectively saturate the downstream signal and linearly amplify the upstream signal, an indispensable feature that is required by the RSOA-EAM to simultaneously erase the downstream signal for a clean seed and to amplify the reloaded upstream signal in its return path. The measurement shows that our fabricated device can reduce the extinction ratio of the 10-Gb/s downstream signal from 5 to 1.2 dB, and a 5-Gb/s upstream signal can be reloaded onto the “clean” carrier, with a clear eye-opening after the linear amplification of its power to over 1 dBm. The measured bandwidth of the device is 25 nm (from 1571 to 1596 nm), far beyond the required 5-nm (from 1575 to 1580 nm) colorless operating range for downstream signals in the 10-Gb/s Ethernet PON and X Gb/s PON.

100 Gb/s SDM-PON Using Polarization-Diversity Silicon Micro-Ring Resonator Enhanced DML

We experimentally demonstrate a bidirectional space-division multiplexing passive optical network system by using a commercial directly modulated laser modulated by a 25 Gb/s NRZ-OOK signal, and followed by a polarization-diversity silicon micro-ring resonator (PolD-MRR) for enhancing the modulation extinction ratio. A multi-core fiber with negligible inter-core crosstalk is used for bidirectional transmission, not only increasing the aggregated capacity but also simplifying the splitting of upstream and downstream and enabling colorless optical network units. The capacity of 100 Gb/s for downstream and 75 Gb/s for upstream has been achieved, respectively. In addition, transmission capacity could be further increased by wavelength-division multiplexing according to PolD-MRR periodical feature, which might be beneficial for future large-capacity optical access networks.

300 Gb/s IM/DD based SDM-WDM-PON with laserless ONUs.

A low-cost, high-speed SDM-WDM-PON architecture is proposed by using a multi-core fiber (MCF) and intensity modulation/directly detection (IM/DD). One of the MCF cores is used for sending laser sources from optical line terminal (OLT) to optical network unit (ONU), thus facilitating laserless and colorless ONUs, and providing ease of network management and maintenance. In addition, the wavelengths of the ONUs are controlled on the OLT side, which also enables flexible optical networks. Thanks to the low inter-core crosstalk of a MCF, downstream (DS) and upstream (US) signals are transmitted independently in different cores of the MCF, not only increasing the aggregated capacity but also avoiding the Rayleigh backscattering noise. Finally, a proof-of-principle experiment is performed by using a 7-core fiber, achieving 300 /120 Gb/s aggregated capacity for DS and US (3 × cores, 4 × wavelengths, 25/10 Gb/s per wavelength), respectively.

Flattened Optical Multicarrier Generation Technique for Optical Line Terminal Side in Next Generation WDM-PON Supporting High Data Rate Transmission

A novel and cost effective optical multicarrier (OMC) generator is introduced in this article. OMC is generated by connecting three modulators in cascade with laser source, where laser is connected with one amplitude modulator and two Mach-Zehnder modulators (MZMs) in cascade. The amplitude modulator is used for the first time in cascade configurations for the generation of OMC signal. All the modulators are driven by RF signal of 30 GHz where specially tailored or fiber-Bragg gratings are not required. The generated OMC is very flat due to the proper DC biasing of MZMs and being related to the optimum ratio of DC bias and half wave voltage of MZMs. OMC offers 61 comb lines with minimum excursions in its comb lines, having tone-to-noise ratio greater than 40 dB, frequency spacing equal to 30 GHz, and high side mode suppression ratio over 35 dB. In this configuration, no optical phase shifter, amplifier, or attenuator is used. Second, optical line terminal (OLT) costs of conventional wavelength division multiplexed passive optical network (WDM-PON) system are reduced by introducing the proposed OMC source at OLT side of WDM-PON system for large capacity WDM-PON that supports numerous users. At OLT side, each out of 61 carriers is capable of supporting 10 Gb/s differential phase shift keying based data in downlink transmission. In the uplink transmission, half power splitters are deployed at optical network unit (ONU) side, where half power of the downlink signal is utilized for uplink transmission based on intensity-modulated on-offkeying resulting in colorless ONUs. The detailed power budget is discussed for the validity of results. Bit error rate (BER), eye patterns, and power penalties lie in the metrics encountered for the analysis in full duplex PON’s transmission. Minimum power penalties at specific BERs of different channels show the applicability of the proposed model.

Wavelength Reuse for Short-Reach Optical Access Network Utilizing MDM

Wavelength reuse has been proposed as an effective solution to realize colorless optical network units (ONUs) for next-generation passive optical network with simplified maintenance and reduced cost. In this paper, we propose a wavelength reused mode-division-multiplexing (MDM) scheme for bidirectional short-reach optical access network with low mode-crosstalk multiplexer/demultiplexer (MUX/DEMUX) and few-mode fiber (FMF). In downstream (DS) transmission, one of the spatial modes in FMF is used to transmit optical carriers, while the others are used as DS signal channels. In upstream (US) transmission, the carrier is split to all the ONUs for US remodulation. By utilizing low mode-crosstalk mode MUX/DEMUX and FMF, the carrier and each signal channel can be effectively separated. Compared with other wavelength reused schemes in which the DS and US transmission are modulated in orthogonal dimension, the signal qualities on two transmission directions are independent in the proposed scheme, and symmetrical bidirectional transmission without residual remodulation crosstalk can be achieved. What is more, to reduce bidirectional Rayleigh backscattering noise, we propose to use different optical sidebands for DS and US transmission. With the proposed scheme, we experimentally demonstrate symmetrical bidirectional 2 × 12.5-Gb/s quadrature phase-shift keying (QPSK) orthogonal-frequency-division-multiplexing (OFDM) intensity-modulation and direct-detection transmission over 11.5-km four-mode FMF. With Rayleigh backscattering noise mitigation, a Q-factor improvement of 2 dB is achieved for the US signal at the DS signal-to-carrier power ratio of −27 dB.

Reconfigurable intensity modulation and direct detection optical transceivers for variable-rate wavelength-division-multiplexing passive optical networks utilizing digital signal processing-based symbol mapper

Variable-rate intensity modulation and direct detection-based optical transceivers with software-controllable reconfigurability and transmission performance adaptability are experimentally demonstrated, utilizing M-QAM symbol mapping implemented in MATLAB® programs. A frequency division multiplexing-based symbol demapping and wavelength management method is proposed for the symbol demapper and tunable laser management used in colorless optical network unit.

10-Gbps optical duobinary signal generated by bandwidth-limited reflective semiconductor optical amplifier in colorless optical network units and compensated by fiber Bragg grating-based equalizer in optical line terminal

We propose a scheme of optical duobinary-modulated upstream transmission system for reflective semiconductor optical amplifier-based colorless optical network units in 10-Gbps wavelength-division multiplexed passive optical network (WDM-PON), where a fiber Bragg grating (FBG) is adopted as an optical equalizer for better performance. The demodulation module is extremely simple, only needing a binary intensity modulation direct detection receiver. A better received sensitivity of −16.98 dBm at bit rate error ( BER)=1.0×10 −4 can be achieved at 120 km without FBG, and the BER at the sensitivity of −18.49 dBm can be up to 2.1×10 −5 at the transmission distance of 160 km with FBG, which demonstrates the feasibility of our proposed scheme. Moreover, it could be a high cost-effectiveness scheme for WDM-PON in the future.

Bidirectional 50 Gb/s/λ WDM-PON based on optical intensity modulation and direct detection

We experimentally demonstrate an optical intensity modulation transmitter with a half-cycle 32 QAM Nyquist subcarrier modulation and direct detection receiver-based channel-reuse wavelength-division-multiplexing passive optical network. Chromatic dispersion-induced power fading in the direct detection system is avoided with fiber Bragg grating filter-based vestigial-sideband filtering. The inter-symbol interference is mitigated with a digital signal processing-based overlap frequency-domain equalizer and iterative distortion-cancellation technique. A frequency division multiplexing-based wavelength management method is employed for the tunable laser used in a colorless optical network unit to achieve a bidirectional 50 Gb/s/λ transmission over a 40 km-long standard single-mode-fiber on a 100 GHz WDM grid. The transmission performance is also measured with different central wavelength shifts between upstream and downstream in the channel-reuse system.

Flexible tunable optical transceiver based on field-programmable gate array for time and wavelength-division multiplexed passive optical network systems

Time- and wavelength-division multiplexed passive optical networks (TWDM-PONs) have been selected by the full services access network community as the most suitable technology for next-generation optical access networks. A key technology in TWDM-PON is the colorless optical network unit transceiver. This paper proposes a flexible, tunable optical transceiver that uses directly modulated tunable lasers. Using a field-programmable gate array (FPGA), programmable reconfigurations and testing capabilities can be embedded into the transceiver in order to implement wavelength control, signal generation, pre-emphasis for upstream, and a bit error rate (BER) test for the downstream. To ensure high-quality signal generation at different bitrates, impedance matching between the laser driver circuit and the laser diodes is optimized. Using the proposed transceiver, three-section-distributed Bragg reflector tunable lasers at or below 2.5 Gb/s direct modulation through a 40-km standard mode fiber transmission were successfully implemented.

Symmetric 10 Gb/s wavelength reused bidirectional RSOA based WDM-PON with DPSK modulated downstream and OFDM modulated upstream signals

A 10Gb/s bidirectional wavelength division multiplexing passive optical network (WDM-PON) with reflective semiconductor optical amplifier (RSOA) based colorless optical network unit (ONU) is proposed and analyzed for next generation gigabit class optical access network. Differential phase shift keying (DPSK) modulated signal is used in downstream and further reused as a seeding wavelength for upstream data modulation. By exploiting the constant envelope property of DPSK seed signal, the re-modulation noise in upstream receiver is effectively minimized without employing any constraint on extinction ratio of downstream signal. Orthogonal frequency division multiplexing (OFDM) signal is used in upstream transmission to overcome the limited bandwidth (∼1GHz) response of RSOA remodulation. The results show that the proposed 10Gb/s symmetric WDM-PON can achieve good performance over 25km fiber transmission with error free operation in downstream and bit error rate (BER) lower than forward error correction (FEC) limit in upstream.

IMDD-based bidirectional 20 Gb/s/λ WDM-PON with Nyquist 4 PAM employing Rayleigh backscattering noise detection-based self wavelength management

We experimentally demonstrate an optical intensity modulation transmitter with a Nyquist 4 level pulse amplitude modulation and direct detection (DD) receiver-based channel-reuse wavelength-division-multiplexing passive optical network (WDM-PON). A Rayleigh backscattering noise detection-based wavelength management method is employed for the tunable optical transmitter used in colorless optical network unit to achieve bidirectional 20 Gb/s/λ transmission over 45-km standard single-mode-fiber on a 100-GHz WDM grid. Chromatic dispersion induced power fading in the DD system is avoided with fiber Bragg grating filter-based vestigial-sideband filtering. The inter-symbol interference is cancelled with digital signal processing-based overlap frequency-domain equalizer. The transmission performance is also measured with different optical signal to Rayleigh backscattering noise ratio and different central wavelength shift between upstream and downstream in the channel-reuse system.

100-km-reach, 40 Gb/s/λ downstream and 10 Gb/s/λ upstream, channel-reuse WDM-PON employing tunable laser with back-reflection optical signal detection-based self wavelength management

We experimentally demonstrate a 100-km-reach, channel-reuse wavelength-division-multiplexing passive optical network (WDM-PON) with 40 Gb/s/λ downstream and 10 Gb/s/λ upstream transmission and a back-reflection optical signal detection-based automatic wavelength control method for a tunable laser used in a colorless optical network unit. Channel-reuse, full-duplex, 40 Gb/s/λ downstream and 10 Gb/s/λ upstream transmission on a 100 GHz WDM grid with 100 km reach was achieved. The transmission performance was measured using different optical signal to back-reflection optical signal ratios, optical signal to Rayleigh backscattering noise ratios, and different central wavelength shifts between the upstream and downstream signals in the channel-reuse system.

Centrally controlled self-healing wavelength division multiplexing passive optical network based on optical carrier suppression technique

We proposed and demonstrated a centrally controlled and self-healing wavelength division multiplexing passive optical network with colorless optical network units (ONUs) based on optical carrier suppression technique. By switching the affected data in the OCS signal sideband to an alternate protection path, only one optical switch is provisioned at the optical line terminal, which is controlled by a logic control circuit upon monitoring of power outage on the working path. The proposed scheme can reliably protect against both distribution and feeder fiber failures. Moreover, gain-saturated reflective semiconductor optical amplifiers are used as colorless transmitters in ONUs. The protection scheme feasibility and system performances are experimentally verified with 10 Gb/s downstream and 1.25 Gb/s upstream data in both working and protection modes. The protection switching time was measured to be around 1 ms.

Bidirectional 40 Gb/s/λ, 100 km-reach, channel-reuse WDM-PON employing tunable optical transceiver with optical intensity detection-based wavelength management

We experimentally demonstrate a channel-reuse, bidirectional 40Gb/s/λ, long-reach wavelength-division-multiplexing passive optical network (WDM-PON) and an optical intensity detection-based wavelength management method for tunable optical transceiver used in colorless optical network unit. A 100km reach, channel-reuse, 40Gb/s/λ transmission on a 100GHz WDM grid is achieved. Transmission performance is also measured with different optical-signal-to-Rayleigh-backscattering-noise ratios (OSRBNRs) and different central wavelength shifts (WSs) between upstream signal and downstream signal in the channel-reuse system. Optimal operating wavelength for the uplink optical signal and effective OSRBNR configurations taking into account AWG pass-band, wavelength instability of the bidirectional optical transmitters are proposed.

Multisignal OFDM-Based Hybrid Optical-Wireless WDM LR-PON With Colorless ONU

We experimentally demonstrate bidirectional transmission in a multisignal orthogonal frequency division multiplexing hybrid optical-wireless long reach passive optical network with a colorless optical network unit (ONU), and the optical seed generated at remote node (RN) 75 km away from optical line termination. The main impairments are quantified and the most limiting is shown to be Rayleigh backscattering beating noise. To overcome it, the ONU optical gain is increased and a transmission reach exceeding 25 km beyond the RN is achieved.

System performance analysis of time-division-multiplexing passive optical network using directly modulated lasers or colorless optical network units

As a promising technology for broadband communication, passive optical network (PON) has been deployed to support the last-mile broadband access network. In particular, time-division-multiplexing PON (TDM-PON) has been widely used owing to its mature technology and low cost. To practically implement TDM-PONs, the combination of intensity modulation and direct detection is a very promising technique because it achieves cost reduction in system installation and maintenance. However, the current intensity-modulation and direct-detection TDM-PON still suffers from some problems, which mainly include a high-power penalty, detrimental Brillouin backscattering (BB), and so on. Thus, using directly modulated lasers (DMLs) and colorless optical network units (ONUs), respectively, two intensity-modulation and direct-detection TDM-PON architectures are proposed. Using VPI (an optical simulation software developed by VPIphotonics company) simulators, we first analyze the influences on DML-based intensity-modulation and direct-detection TDM-PON (system 1) performances, which mainly include bit error rate (BER) and power penalty. Next, the BB effect on the BER of the intensity-modulation and direct-detection TDM-PON that uses colorless ONUs (system 2) is also investigated. The simulation results show that: (1) a low-power penalty is achieved without degrading the BER of system 1, and (2) the BB can be effectively reduced using phase modulation of the optical carrier in system 2.

Bidirectional 10 Gb/s/λ, channel-reuse, long-reach DWDM-PON employing tunable optical transceiver with optical intensity detection-based wavelength management

We experimentally demonstrate a channel-reuse, bidirectional 10 Gb/s/λ, long-reach dense wavelength-division-multiplexing passive optical network (DWDM-PON) and an optical intensity detection-based wavelength management method for tunable optical transceiver used in colorless optical network unit. A channel-reuse, full-duplex, 42 km/87 km reach without/with optical amplification, 10 Gb/s transmission on a 50 GHz DWDM grid is achieved. Transmission performance is also measured with different optical-signal-to-Rayleigh-backscattering-noise ratios (OSRBNRs) and different central wavelength shifts between upstream signal and downstream signal in the channel-reuse system. Optimal operating wavelength for the uplink optical signal and effective OSRBNR configurations taking into account AWG pass-band, wavelength instability of the downlink optical transmitter and the distance of the feeder fiber are proposed.