Active Demultiplexing Research Articles

Integrated Comb Laser With Active De-Multiplexer for Spectrally Sliced Coherent Receiver

Integrated Comb Laser With Active De-Multiplexer for Spectrally Sliced Coherent Receiver

Resource-efficient low-loss four-channel active demultiplexer for single photons

We report a design and implementation of a resource-efficient spatial demultiplexer which produces four indistinguishable photons with efficiency of 39.7% per channel. Our scheme is based on a free-space storage/delay line which accumulates four photons and releases them by a controlled polarization rotation using a single Pockels cell.

Resource-efficient low-loss four-channel active demultiplexer for single photons

We report a design and implementation of a resource-efficient spatial demultiplexer which produces four indistinguishable photons with efficiency of 39.7% per channel. Our scheme is based on a free-space storage/delay line which accumulates four photons and releases them by a controlled polarization rotation using a single Pockels cell.

Generation of a Wideband OFC by the Correlation of Multiple Modes of a Gain-Switched Fabry Pérot Laser

We experimentally demonstrate two novel photonically integrable architectures of a wideband gain-switched optical frequency comb (OFC). The proposed method is based on correlating multiple modes of gain-switched Fabry-Pérot (GS-FP) laser. This is achieved by injection locking a GS-FP with an optimised signal generated by an source OFC and a dual-stage active demultiplexer. By employing such a configuration, we demonstrate the generation of two 6.25 GHz OFCs, spanning over 337.5 GHz and 875 GHz with expansion factors of 4 and 10, respectively. The optimisation of the OFC expansion for flatness and/or wide span, as required is also shown. Furthermore, a detailed comb line characterisation is reported, to highlight the spectral purity of the expanded comb portraying low linewidth (∼85 kHz), a low relative intensity noise (RIN better than -130 dB/Hz), and a high degree of phase correlation between lines (13 Hz beat tone width). Finally, active demultiplexing of the comb lines with various separations across the expanded OFC is reported, demonstrating its suitability for use in a superchannel-based flexible optical networks, mmW/THz generation and spectroscopy applications.

Fast and efficient demultiplexing of single photons from a quantum dot with resonantly enhanced electro-optic modulators

We report on a multi-photon source based on active demultiplexing of single photons emitted from a resonantly excited GaAs quantum dot. Active temporal-to-spatial mode demultiplexing is implemented via resonantly enhanced free-space electro-optic modulators, making it possible to route individual photons at high switching rates of 38 MHz. We demonstrate routing into four spatial modes with a high end-to-end efficiency of ≈ 79% and measure a four-photon coincidence rate of 0.17 Hz mostly limited by the single-photon source brightness and not by the efficiency of the demultiplexer itself. We use the demultiplexer to characterize the pairwise indistinguishability of consecutively emitted photons from the quantum dot with variable delay time.

Optical Linewidth Tolerant mmW Generation Employing a Dual-Stage Active Demultiplexer

In this letter, we propose a novel linewidth tolerant millimetre-wave (mmW) generation scheme employing a dual-stage active demultiplexer and an optical frequency comb (OFC). A unique feature of this architecture is that the two heterodyned tones travel the same path, alleviating the challenges associated with mismatches in the path lengths. We analyse the influence of the path length difference and source linewidth on the purity of the generated mmW signal and verify the tolerance, of the proposed scheme, to the optical linewidth. In addition, an experimental investigation of the performance of a 64 QAM discrete multitone (DMT) analog-radio over fibre (A-RoF) distribution system operating at 37.5 GHz using the proposed architecture, is presented. A BER below the HD-FEC limit is achieved, after 25 km fibre transmission, when employing an OFC with linewidth of ~30 kHz and ~3.1 MHz. Moreover, no significant performance penalty (at the HD-FEC limit) is observed due to an increase in the OFC linewidth, highlighting the linewidth tolerance of the proposed system.

Tunable Mm-Wave A-RoF Transmission Scheme Employing an Optical Frequency Comb and Dual-Stage Active Demultiplexer

Anovel dual-stage optical frequency comb (OFC) demultiplexer, for use in a photonic millimeter-wave (mmW) generator, is demonstrated. Unlike other demultiplexing techniques, the proposed method features a single optical path for both tones used for the mmW generation, thus eliminating the challenges related to the mismatch of path lengths. In addition, the use of active demultiplexing provides filtering, amplification and data modulation of the comb tones, all in a single device. In this article, we demonstrate the operational principle of the dual-stage active demultiplexer-enabled mmW generation, verify the quality (beat tone width ∼13 Hz) and stability (power fluctuation ∼0.26 dB) of the generated mmW signal and validate the performance of an A-RoF system employing the proposed device. For the system demonstration, 64-QAM UF-OFDM signals, at frequencies of 29.5 and 38 GHz, are generated and transmitted over 25 km of single-mode fiber. A BER of 3.2e-4 for 29.5 GHz and 1.6e-4 for 38 GHz is achieved without the use of optical amplifiers, showing the great potential of the proposed technique. Finally, a case study of an A- RoF distribution system, employing three different demultiplexing techniques, is presented. We demonstrate that the proposed transmitter, in comparison to other demultiplexing techniques, provides a larger power budget (> 6 dB) that can be used to extend the reach of the system and/or increase the number of remote radio units served using a single OFC.

Active Demultiplexer-enabled Directly Modulated DMT Transmission Using Optical Frequency Combs for Data Center Interconnects

In this paper, we experimentally demonstrate an optical frequency comb (OFC) based transmitter, employing directly modulated active demultiplexers, for data center interconnects. The results validate that the proposed transmitter has the potential to achieve aggregate data rates of 100 Gb/s (8 × 12.5 Gb/s) and 200 Gb/s (8 × 25 Gb/s) for systems employing 4- and 16- quadrature amplitude modulated (QAM) discrete multi-tone (DMT) modulation. An OFC based on an externally injected gain switched laser (EI-GSL) is used, providing excellent stability and flexibility in free spectral range (FSR). The OFC is followed by an injection locked active demultiplexer, which not only filters, but also amplifies individual comb tones, thus alleviating the need for an external optical amplifier to boost the low powered comb tones. Using the proposed configuration, we experimentally demonstrate a successful transmission of 12.5 Gb/s/λ 4-QAM DMT and 25 Gb/s/λ 16-QAM DMT signals over 40 km and 25 km of SSMF, respectively. In addition, we show that it is possible to filter and modulate comb lines that are 20 dB below the spectral peak, whilst achieving a BER below the hard decision (HD-) FEC limit of 3.8e-3. This gain flattening or comb expansion feature leads to a significant increase in the channel count, which in turn provides a reduction in the energy consumption and the footprint of the transmitter.

Characterization of a multifunctional active demultiplexer for optical frequency combs

We report on a multifunctional active demultiplexer for optical frequency combs. The proposed technique, based on injection locking, combines the functionality of a tunable demultiplexer, gain equalizer and an optical amplifier, all in one device. Validation of the concept is experimentally demonstrated through simultaneous demultiplexing and amplification of combs with various free spectral ranges (2.5 to 15 GHz), achieving an adjacent channel suppression ratio > 35 dB and an output power of 7.5 dBm. The functionality of the demultiplexer is extended to that of a gain equalizer, by filtering comb tones with powers 10 dB below the spectral peak, whilst maintaining a suppression ratio > 30 dB and a constant output power. This feature increases the number of comb lines suited for data modulation (i.e. usable lines), by a factor of ~1.7. Finally, we test the stability of such a demultiplexer, by measuring the frequency drift, beat tone power variations and phase correlation between demultiplexed tones.

Active demultiplexer enabled mmW ARoF transmission of directly modulated 64-QAM UF-OFDM signals.

In this Letter, we experimentally demonstrate an unamplified analog RoF distribution of 60 GHz 5G signals. The system entails the heterodyning of two optical tones from an externally injected gain switched laser (EI-GSL) based optical frequency comb to generate a millimeter wave (mmW) signal. A fixed frequency separation and a high level of phase correlation, between the EI-GSL comb lines, results in the generation of a high-quality signal. An active demultiplexer is used to filter and amplify two comb tones, thus alleviating the need for an external optical amplifier to boost the low power comb tones. Furthermore, the same demultiplexer is also used to modulate one of the tones with a 64-QAM UF-OFDM signal. Such an approach enables the remote generation of a mmW downlink data signal as well as an unmodulated RF carrier that could be used to downconvert the mmW signals to an intermediate frequency. Using the abovementioned scheme, we demonstrate the distribution of the downlink signal over 25 km of fiber, achieving a BER of 2.4e-3 (below the HD-FEC limit of 3.8e-3) and only a 0.5 dB penalty at the FEC limit in comparison to the BtB case.

Efficient demultiplexed single-photon source with a quantum dot coupled to a nanophotonic waveguide

Planar nanostructures allow near-ideal extraction of emission from a quantum emitter embedded within, thereby realizing deterministic single-photon sources. Such a source can be transformed into M single-photon sources by implementing active temporal-to-spatial mode demultiplexing. We report on the realization of such a demultiplexed source based on a quantum dot embedded in a nanophotonic waveguide. Efficient outcoupling (>60%) from the waveguide into a single mode optical fiber is obtained with high-efficiency grating couplers. As a proof-of-concept, active demultiplexing into M = 4 spatial channels is demonstrated by the use of electro-optic modulators with an end-to-end efficiency of >81% into single-mode fibers. Overall, we demonstrate four-photon coincidence rates of >1 Hz even under nonresonant excitation of the quantum dot. The main limitation of the current source is the residual population of other exciton transitions, which corresponds to a finite preparation efficiency of the desired transition. We quantitatively extract a preparation efficiency of 15% using the second-order correlation function measurements. The experiment highlights the applicability of planar nanostructures as efficient multiphoton sources through temporal-to-spatial demultiplexing and lays out a clear path way of how to scale up toward demonstrating quantum advantages with the quantum dot sources.

Active demultiplexing of single photons from a solid‐state source (Laser Photonics Rev. 11(3)/2017)

Single photons from a solid state source are deterministically routed into different output modes by a fully integrated active optical switch network. Using a state-of-the-art single photon source made of a single quantum dot in a micropillar cavity and an innovative integrated optical demultiplexer, this scheme is capable of creating manifold single photon states. Such states are a crucial resource for photonic quantum information applications including linear optics quantum computation and quantum communications. (Picture: Mirko Lobino, Ph.D. et al., article number 1600297, in this issue)

Active demultiplexing of single photons from a solid‐state source

AbstractA scheme for active temporal‐to‐spatial demultiplexing of single photons generated by a solid‐state source is introduced. The scheme scales quasi‐polynomially with photon number, providing a viable technological path for routing n photons in the one temporal stream from a single emitter to n different spatial modes. Active demultiplexing is demonstrated using a state‐of‐the‐art photon source—a quantum‐dot deterministically coupled to a micropillar cavity—and a custom‐built demultiplexer—a network of electro‐optically reconfigurable waveguides monolithically integrated in a lithium niobate chip. The measured demultiplexer performance can enable a six‐photon rate three orders of magnitude higher than the equivalent heralded SPDC source, providing a platform for intermediate quantum computation protocols. image

Migrating sockets-end system support for networking with quality of service guarantees

We present an end system architecture designed to support networking with quality of service (QoS) guarantees. The protocol processing component of the architecture, called migrating sockets, has been designed with minimal hidden scheduling which enables accurate determination of the rate requirement of a user application. The end system provides QoS guarantees using: 1) an adaptive rate-controlled scheduler; 2) rate-based flow control on the send side for access to reserved-rate network connections; and 3) a constant overhead active demultiplexing mechanism on the receive side which can be transparently enabled in wide-area TCP/IP internetworking (although it is not restricted to TCP/IP). To achieve efficiency, migrating sockets lets user applications manage network endpoints with minimal system intervention, provides user level protocols read-only access to routing information, and integrates kernel level support previously built for efficient data movement. Migrating sockets is backward compatible with Unix semantics and Berkeley sockets. It has been used to implement Internet protocols such as TCP, UDP, and IP (including IP multicast), and run existing applications such as vic. Migrating sockets has been implemented in Solaris 2.5.1. We discuss our implementation experience, and present performance results of our system running on Sun Sparc and Ultra workstations, as well as Pentium-II desktops.