We demonstrate an effective approach to compensate fabrication imperfections in an integrated coherent receiver for PONs. This approach, based on adjusting the local oscillator state of polarization, compensates the non-ideal polarization separation in the integrated Polarization Beam Splitter (PBS), resulting in a polarization-independent receiver. (c) 2025 The Authors.

En este trabajo presentamos un nuevo método basado en el ajuste del estado de polarización del oscilador local de un receptor coherente integrado para compensar los errores de fabricación y hacerlo insensible a la polarización de la señal de entrada.

Traditional Intensity Modulation/Direct Detection (IM/DD) based Passive Optical Networks (PONs) face limitations, including poor sensitivity and chromatic dispersion issues, as well as frequency fading for high data bit rates, which make coherent receivers a promising alternative for PONs. Coherent receivers improve optical power budgets, enhance spectral efficiency, and mitigate chromatic dispersion issues. However, their deployment in access networks remains challenging due to the cost associated with additional components such as local oscillator (LO) lasers, high frequency electronics and polarization management devices. In this paper, we discuss these constraints and present our approaches to achieve low-cost coherent heterodyne polarization independent receivers for 50/100 Gb/s PONs. Starting with a simplified polarization-insensitive heterodyne coherent receiver for 50 Gb/s, we analyze the roadmap to a DSP-enabled PolMux heterodyne coherent receiver for up to 100 Gb/s. All these approaches rely on low-cost 10G optoelectronics and can be easily integrated into miniatured Photonic Integrated Circuits (PICs).

In this work, we experimentally demonstrate a ${100}\;{\rm Gb/s/}\lambda$ downstream transmission link for coherent passive optical networks (PONs) up to 50 km, achieving an optical power budget of 29 dB through polarization multiplexing (PolMux) of two 50 Gb/s channels using multiband carrierless amplitude phase modulation (multiCAP) and optical single side band (OSSB) modulation. Additionally, we introduce a separate PolMux 50 Gb/s link that presents an optical power budget of 38.7 dB. Both links have been achieved using a simplified polarization-demultiplexing heterodyne coherent receiver. The robustness of the system is experimentally evaluated by analyzing its response to various input states of polarization. The transmission has been accomplished using 10 GHz electrical bandwidth devices at both the transmission and receiving ends, thereby paving the way for low-cost 100G links suitable for applications such as PONs.

Intradyne coherent receivers, capable of detecting an individual wavelength-division multiplexed channel just by tuning the local oscillator frequency, is of great interest for the development of high-capacity flexible optical networks. Nevertheless, the unavoidable amplitude imbalances inherent to any realistic coherent receiver induce an interference contribution from the self-beating of the coincident channels present at its input. The characterization of this degraded colorless reception operation is of fundamental importance, but it usually requires the use of rather complex experimental setups, especially when the effects of tens of interference channels should be evaluated. In this work we propose a novel experimental setup that only requires the use of a single intense interferer to emulate those coincident channels, thus drastically simplifying the characterization process. In addition, we develop a general expression for the signal-to-noise ratio of the system that theoretically justifies the intended setup and demonstrate by massive numerical simulations its accuracy in different scenarios. We believe that the proposed approach may contribute to facilitate the experimental characterization of high-performance colorless coherent receivers.

Nowadays, 25 Gbps to 100 Gbps single-wavelength Passive Optical Network (PON) links are expected to become the next generation optical access networks and coherent PONs represent an interesting option to overcome the poor sensitivities of traditional direct detection (DD) at these high data rates. However, coherent schemes need complex Digital Signal processing (DSP) and are polarization sensitive. Different solutions have been proposed to make coherent receivers insensitive to polarization but, in this work, we propose a different approach using a Glance heterodyne polarization insensitive receiver [1], [2] as a PolMux receiver to double the bit rate. Although digital recovery of the PolMux data has been widely studied for intradyne schemes, it has been completely redesigned and implemented for our heterodyne scheme including a four independent complex coefficients rotation matrix, instead of the classical two coefficients commonly used in intradyne schemes, and an autonomous and automatic training of the matrix.

We present a 100Gb/s downstream PON link based on a PolMux, multi-CAP OSSB modulation signal received by a coherent receiver. 50km transmission is achieved using 10G electronic and photonic devices with a sensitivity of -20dBm.

We present a 50Gb/s downstream PON link based on a PolMux 32QAM-MultiCAP modulation and a heterodyne choherent receiver with DSP based PolDemux. 25km transmission is achieved using 10G electronic and photonic devices with a sensitivity of -25dBm for the worst band and polarization.

Optical access networks are already installed throughout the world, being the cornerstone for home and office high bandwidth communications. 50 Gb/s and 100 Gb/s single-wavelength PON links are being studied as they are expected to be the next step towards the future optical access networks [1] . Many works have explored different techniques to achieve 50 Gb/s links using 25 GHz or 10 GHz bandwidth components and IM/DD schemes. While 25G based solutions are usually based on PAM4, which provides a simple solution by doubling the bit count [2] , 10G based solutions need to increase even more the bit count per Hz, so most of the proposals use OFDM or Multi-CAP modulation schemes [3] – [4] . However, all these non-coherent solutions present poor sensitivities at the receiver, needing to increase the signal power at transmission to achieve adequate optical power budgets. Moreover, these schemes suffer from power fading at some frequencies when propagating through the optical fiber. In this work, we use Multi-CAP modulation as well as an optical Hilbert transformed OSSB scheme [5] for the transmission of spectrally efficient signals. This allows using power and bit loading capabilities and flexibility of the Multi-CAP modulation to transmit a 50 Gb/s bitrate while maintaining a narrow electrical and optical spectral bandwidth of 11.25 GHz, allowing the use of 10G electronics at both, transmitter and receiver side and avoiding the power fading issue without any additional digital processing. At the receiver side, we use a well-known polarization-insensitive heterodyne coherent scheme that will boost the sensitivity of the receiver and eliminate the use of tunable optical filters in a WDM system. Moreover, we use it as a PolMux receiver to double the data rate by inserting two 50 Gb/s orthogonal polarizations for an aggregated 100 Gb/s downstream link. This receiver presents a sensitivity of -22 dBm BTB and ~2dB penalty over 50 km transmission link. The obtained optical power budget is about 21 dB for the worst Multi-CAP band and PolMux channel.

In this paper, a spectrally efficient version of multiband Carrierless Amplitude Phase modulation (MultiCAP) based on Optical Single-Sideband (OSSB) techniques is proposed for its use in high capacity access links. The proposed system consists of four 2.5 GBd OSSB-MultiCAP bands with quadrature amplitude modulation and uses an insensitive polarization receiver to avoid optical polarization issues and adjustments at the receiver side. This scheme has been experimentally evaluated and can provide an aggregated transmission rate of 50 Gb/s over 50 km of standard single mode optical fiber using only 10G electronic and photonic devices in C-band with a sensitivity of -23.2 dBm and a measured optical power budget of 25.2 dB. 40 Gb/s transmission over 50 km with a sensitivity of -27.5 dBm and a measured power budget of 32.5 dB is also demonstrated.

A combined non-orthogonal multiple access (NOMA) and multiband carrierless amplitude and phase modulation (multiCAP) scheme is proposed for flexible resource provisioning in coherent passive optical networks (PONs). While the proposed combination increases the data-rate and the number of users through the inclusion of NOMA and multiCAP, the coherent reception increases the range and splitting factor of the network through optical power budget enhancement. The proposed system is experimentally evaluated providing a 20 Gb/s aggregated data-rate per wavelength with 10G optoelectronics and applied in two main PON scenarios with four spectral configurations from full-band CAP to four-band multiCAP. The first PON scenario consists of an existing PON that the network operator requires to increase the number of users; NOMA with full-band CAP or multiCAP can be introduced replacing one or more users of the existing PON by one or several new sub-networks and multiplexing the sub-networks by NOMA. In the other PON scenario, several PONs can be nested sharing an initial splitter and achieving a larger number of users by the combination of NOMA and multiCAP. The proposed techniques are fully compatible with other multiplexing techniques such as dense wavelength division multiplexing, which should be considered to achieve higher numbers of users.

The performance of an integrated InP 120° coherent receiver has been experimentally analyzed using 50 Gbps 16-QAM signals. IQ components are obtained through a set of coefficients applied to the three output photocurrents of the device. It is demonstrated that the calibration of these coefficients can compensate, without extra computational cost, fabrication hardware impairments and allows a wide optical bandwidth (up to 80 nm range) with a high interfering rejection capability. It has been experimentally verified colorless operation in the complete C-band for a received interfering power close to 11 dB above the signal level. This confirms a remarkable colorless behavior of our proposal.

Quasi-coherent receivers have been demonstrated as a powerful technology for addressing the requirements of the current optical networks based on 10 Gbps line rate. The quasi-coherent technology also has a promising future in the next generation of optical networks where the line rate scales up to 25 Gbps or 50 Gbps. In this paper, the current 10 Gbps quasi-coherent technology has been summarized, together with the first results at 25 Gbps. In addition, this paper shows the roadmap of the future updates of the quasi-coherent technology addressing the necessities of the future optical networks.

The constant growth of traffic demand caused by IoT, cloud computing, and streaming services on personal devices, requires changes in architecture and more sophisticated schemes by pushing forward 5G optical fronthaul applications. An experimental assessment of NOMA-CAP modulation is performed for future fronthauling in beyond 5G scenarios with IM-DD systems for a cost-effective implementation. Two transmitters are compared: an intensity modulated VCSEL as cheapest implementation; versus a tuneable laser source externally modulated by a MZM as reference of best quality. In addition, the sensitivity at 7% overhead FEC limit for two alternative receivers are analysed for a data rate of 14Gbps over 50km of SSMF in 4GHz electrical bandwidth, providing values of -13dBm (PIN) and -25dBm (APD). Moreover, a practical approach for APD is validated by comparison of a PIN with a filtered EDFA pre-amplifier, and an APD based SFP transceiver showing a small sensitivity difference of 0.1dB to 0.5dB.

Non-Orthogonal Multiple Access (NOMA) technique and Carrierless Amplitude Phase (CAP) modulation have been used to demonstrate pay-as-you-grow coherent Passive Optical Networks (PON) and providing a 10 Gbps aggregate data rate.

Coherent technologies are exhibiting the flexibility and performance required to address the next generation of optical access networks, where the residential, business and mobile backhaul will converge. The use of these technologies for access networks is approached from several angles, including affordable photonic integrated circuits (PICs) and cost-effective transceivers are met. In this work, we will present different technologies we have been working on lately, as a low cost 2x3 coherent PIC receiver, which allows an increment of the overall capacity of the network. We will also show cost-effective coherent transceiver components, e.g. directly-phase modulated VCSELs transmitters and/or quasi-coherent receivers, which can play an important role in reducing cost while still fulfilling the future capacity. New advanced modulation formats may also contribute to this goal, by allowing the introduction of new concepts as pay-as-you-grow upgrades through the employment of non-orthogonal multiple access (NOMA) technique combined with e.g. carrierless amplitude phase modulation (CAP). Finally, we will also study the use of intensity modulated spectrally efficient formats as OFDM, FBMC, UFMC and GFDM in an optical access network architecture.

Este articulo presenta un receptor cuasicoherente de 25Gbps con un DSP sencillo para redes de acceso futuras. Este receptor cuasicoherente de 25Gbps con decodificación duobinaria presenta una sensibilidad de ‑24.7dBm tras la transmisión a través de 20km de fibra y provee un balance de potencia de 25.7dB.

Performance of an integrated 120° coherent receiver has been experimentally analysed using 10Gb/s 16-QAM signals. The calibration of the coefficients for the IQ components recovery allows a 100nm colorless behaviour and high interfering rejection capability without extra computational cost.