Yongchi Xu

Wideband tunable optoelectronic oscillator based on the deamplification of stimulated Brillouin scattering

A wideband tunable optoelectronic oscillator (OEO) based on the deamplification of stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. A tunable single passband microwave photonic filter (MPF) utilizing phase modulation and SBS deamplification is used to realize the tunability of the OEO. Theoretical analysis of the MPF and phase noise performance of the OEO are presented. The frequency response of the MPF is determined by the + 1st sideband attenuation due to SBS deamplification and phase shift difference between the two sidebands due to chromatic dispersion and SBS. The close-in (< 1 MHz) phase noise of the proposed OEO is shown to be dominated by the laser frequency noise via phase shift of SBS. The conversion of the laser frequency noise to the close-in phase noise of the proposed OEO is effectively reduced compared with the OEO based on amplification by SBS. Tunable 7 to 40 GHz signals are experimentally obtained. The single-sideband (SSB) phase noise at 10 kHz offset is -128 dBc/Hz for 10.30 GHz signal. Compared with the OEO based on SBS amplification, the proposed OEO can achieve a phase noise performance improvement beyond 20 dB at 10 kHz offset. The maximum frequency and power drifts at 10.69 GHz are within 1 ppm and 1.4 dB during 1000 seconds, respectively. To achieve better close-in phase noise performance, lower frequency noise laser and higher pump power are preferred. The experimental results agree well with the theoretical models.

Cost effective wavelength reused MDM system for bidirectional mobile fronthaul.

In this paper, we propose a cost-effective wavelength-reused mode-division-multiplexing (MDM) system for high speed symmetrical bidirectional mobile fronthaul application. At the base band unit (BBU) pool, one of the spatial modes is used to transmit signal carrier while the others are used for downstream (DS) signal channels. At the remote radio unit (RRU) side, the signal carrier is split and reused as modulation carrier for all the upstream (US) signal channels after mode demultiplexing. Thanks to the low mode crosstalk characteristic of the mode multiplexer/demultiplexer (MUX/DEMUX) and few-mode fiber (FMF), the signal carrier and each signal channel can be effectively separated. The spectral efficiency (SE) is significantly enhanced when multiple spatial channels are used. Compared with other wavelength reused scheme in which the downstream and upstream be modulated in orthogonal dimension, the modulation format of both directions are independent in the proposed wavelength reused MDM system. Therefore, it can easily achieve symmetrical bidirectional transmission without residual re-modulation crosstalk. The proposed scheme is scalable to multi-wavelength application when wavelength MUX/DEMUX is utilized. With the proposed scheme, we demonstrate a proof of concept intensity modulated 4 × 25-Gb/s 16-QAM orthogonal frequency division multiplexing (OFDM) transmission over 10-km FMF using low modal-crosstalk two-mode FMF and MUX/DEMUX with error free operation. The downstream receiver sensitivity is -21 dBm while the upstream receiver sensitivity is -18 dBm for bidirectional transmission. Due to the Rayleigh backscattering and other spurious reflections, the upstream suffers 2 dB power penalty compared with unidirectional transmission without downstream. To mitigate bidirectional transmission impairments, we propose a simple and effective method to suppress Rayleigh backscattering by shifting the downstream subcarrier frequency. A receiver sensitivity improvement of up to 2.5 dB is achieved for upstream with different downstream power.

Influence of Slow Light on Optoelectronic Oscillators based on Stimulated Brillouin Scattering

48.9-ns delay via slow light in optoelectronic oscillators based on stimulated Brillouin scattering is experimentally measured by side-modes shifting in the phase noise curve. The result demonstrates a potential fine tuning approach in optoelectronic oscillators

Sensitivity improvement of phase noise measurement system using photonic-delay based frequency discriminator

By suppressing the additive phase noise induced by light scattering in the optical fiber and optical interference due to the optical reflection in a microwave phase noise measurement system using photonic-delay based frequency discriminator, the sensitivity improvement of 10 dB is experimentally achieved. Using the proposed measurement scheme, a single sideband phase noise is measured to be −145 dBc/Hz at 10 kHz offset for a 10-GHz OEO.

10 GHz low timing-jitter and broadband optical comb generation based on an optoelectronic oscillator

10 GHz repetition rate, low timing-jitter and broadband optical comb generation based on a low phase noise optoelectronic oscillator is experimentally demonstrated. 10 GHz repetition rate optical comb and 10 GHz RF signal are obtained, simultaneously. A timing-jitter of 52.8 fs (integral range from 100 Hz to 1 MHz) for the optical comb and a phase noise of −132 dBc/Hz at 10 kHz offset for the RF signal are experimentally achieved. The influence of laser frequency noise on the timing-jitter of the optical comb is also investigated.

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.

Experimental Demonstration of Flexible Multicasting and Aggregation Functionality for TWDM PON

Flexible multicasting and aggregation functionality are proposed for TWDM PON utilizing multiple-pump FWM and cyclic AWG. A proof-of-concept 10-Gb/s OOK and QPSK-OFDM signal multicasting and aggregation to seven PON links are experimentally demonstrated.

Widely tunable optoelectronic oscillator utilizing an optical notch filter based on the deamplification of stimulated Brillouin scattering

A novel tunable optoelectronic oscillator utilizing an optical notch filter based on stimulated Brillouin scattering is demonstrated. Tunable 3.36 to 31.4 GHz signals with phase noise of -120 dBc/Hz at 10 kHz offset are obtained.