Optical Sideband Filter Research Articles

Bidirectional wavelength-division-multiplexing fibre-free-space optical communications using polarisation multiplexing technique and tunable optical vestigial sideband filter

To address the growing demand from emerging applications, high transmission capacity is essential for both fibre backbones and last-mile communications. This can be achieved by integrating optical fibre with optical wireless technologies, facilitating the development of fibre-free-space optical communications. Here we report a bidirectional wavelength-division-multiplexing fibre-free-space optical communication employing polarisation multiplexing technique and tunable optical vestigial sideband filter. The transmission capacity is considerably increased by integrating the polarisation multiplexing technique with the wavelength-division-multiplexing scheme. The transmission performance is extensively enhanced by using a tunable optical vestigial sideband filter and vestigial sideband-four-level pulse amplitude modulation. Moreover, the optical wireless link is substantially extended through the operation of triplet lenses. Low bit error rates and clear vestigial sideband-four-level pulse amplitude modulation eye diagrams are attained with a high aggregate transmission capacity of 480 Gb/s for downstream/upstream transmission. This capability of bidirectional fibre-free-space optical communications holds substantial potential for enhancing advanced wired-wireless communications.

RF Self-Interference Cancellation Using Phase Modulation and Optical Sideband Filtering

A novel optical approach to implement RF self-interference cancellation for full-duplex communication using phase modulation and optical sideband filtering is proposed and demonstrated experimentally. Based on the inherent out-of-phase property between the left and right sidebands of phase-modulated signal and optical sideband filtering, the RF self-interference cancellation is achieved by tuning the delay time and amplitude in the optical domain. RF self-interference cancellation for single frequency and microwave with various bandwidths of 1, 5, and 10 MHz is experimentally demonstrated to verify the proposed technique.

A Tunable Si3N4 Integrated True Time Delay Circuit for Optically-Controlled K-Band Radio Beamformer in Satellite Communication

In this paper we present the design, realization, and experimental characterization of a photonic integrated true time delay circuit on a CMOS-compatible Si3N4 platform. The true time delay circuit consists of an optical side band filter for single side band modulation and an optical ring resonator for broadband time delay. Two methods of optical delay tuning are investigated: 1) optical wavelength and 2) thermo-optic delay tuning. The wavelength controlled tuning enables a large delay tuning range and can be done remotely from a distant location. The close to a linear phase measurements can be used for full beam-scanning of radio signals with frequencies in the 20 GHz band. The thermal control results in a 5 GHz RF delay bandwidth. A proof-of-concept 2 × 1 beamforming is demonstrated in the 20 GHz band. The design presented here can be employed to realize multi-beams for multi-users serviced by multiple satellites.

Simultaneous even- and third-order distortion suppression in a microwave photonic link based on orthogonal polarization modulation, balanced detection, and optical sideband filtering.

A microwave photonic link (MPL) with simultaneous suppression of the even-order and third-order distortions using a polarization modulator (PolM), an optical bandpass filter (OBPF), and a balanced photodetector (BPD) is proposed and experimentally demonstrated. The even-order distortions are suppressed by utilizing orthogonal polarization modulation based on the PolM and balanced differential detection based on the BPD. The third-order distortions (IMD3) are suppressed by optimizing the spectral response of the OBPF with an optimal power ratio between the optical carrier and the sidebands of the phase-modulated signals from the PolM. Since the suppression of the IMD3 is achieved when the MPL is optimized for even-order distortion suppression, the proposed MPL can operate with simultaneous suppression of the even-order and third-order distortions. The proposed MPL is analyzed theoretically and is verified by an experiment. For a two-tone RF signal of f1 = 10 GHz and f2 = 19.95 GHz, the spurious-free dynamic range (SFDR2) is enhanced by 23.4 dB for the second harmonic (2f1), and 29.1 and 27.6 dB for the second intermodulation (f2-f1 and f1 + f2), as compared with a conventional MPL. For a two-tone RF signal of f1 = 9.95 GHz and f2 = 10 GHz, the SFDR3 is increased by 13.1 dB as compared with a conventional MPL.

Long reach colorless WDM OFDM-PON using direct detection OFDM transmission for downstream and OOK for upstream

Here we have proposed a novel architecture of wavelength division multiplexed orthogonal frequency division multiplexing (OFDM)-passive optical network (WDM OFDM-PON) which is capable of transmitting 10 Gbps data both in downstream and upstream directions up to 50 km. Here direct detection OFDM is used for downstream unicast transmission and simple on–off keying data is used for upstream unicast transmission. OFDM eliminates inter-symbol interference through use of a cyclic prefix also provides good protection against co-channel interference and impulsive parasitic noise. Since delay interferometer (DI) acts as a optical equalizer and vestigial sideband filter hence a DI is used at central office for successful transmission of 10 Gbps upstream data up to 50 km using reflective semiconductor optical amplifier at optical network unit (ONU) having bandwidth of 1.5 GHz. Since no extra laser source is used at ONU and downstream data is further used for upstream data modulation so colorless scheme is implemented. Simulation is performed for all downstream and upstream channels having data rate of 10 Gbps with a transmission distance of 50 km having acceptable performance.

Integrated Photonic ${\rm K}_{\rm u}$-Band Beamformer Chip With Continuous Amplitude and Delay Control

We present the first demonstration of a broadband and continuously tunable integrated optical beamforming network (IOBFN) capable of providing continuously tunable true-time-delay up to 236 ps over the entire DVB-S band (10.7-12.75 GHz), realized with a CMOS compatible process. The tunable delays are based on reconfigurable optical ring resonators in conjunction with a single optical sideband filter integrated on the same optical chip. The delays and filter responses are software programmable. Four tunable delay lines are integrated on a single chip and configured to feed a 16-element linear antenna array. The broadband beam steering capability of the proposed IOBFN is demonstrated by the squint-free antenna pattern generated from the measured RF amplitude and phase responses of the optical delay line.

On-chip CMOS compatible reconfigurable optical delay line with separate carrier tuning for microwave photonic signal processing

We report, for the first time, an integrated photonic signal processor consisting of a reconfigurable optical delay line (ODL) with a separate carrier tuning (SCT) unit and an optical sideband filter on a single CMOS compatible photonic chip. The processing functionalities are carried out with optical ring resonators as building blocks. We show that the integrated approach together with the use of SCT technique allows the implementation of a wideband, fully-tunable ODL with reduced complexity. To highlight the functionalities of the processor, we demonstrate a reconfigurable microwave photonic filter where the ODL has been configured in a bandwidth over 1 GHz.

Novel Ring Resonator-Based Integrated Photonic Beamformer for Broadband Phased Array Receive Antennas—Part I: Design and Performance Analysis

A novel optical beamformer concept is introduced that can be used for seamless control of the reception angle in broadband wireless receivers employing a large phased array antenna (PAA). The core of this beamformer is an optical beamforming network (OBFN), using ring resonator-based broadband delays, and coherent optical combining. The electro-optical conversion is performed by means of single-sideband suppressed carrier modulation, employing a common laser, Mach-Zehnder modulators, and a common optical sideband filter after the OBFN. The unmodulated laser signal is then re-injected in order to perform balanced coherent optical detection, for the opto-electrical conversion. This scheme minimizes the requirements on the complexity of the OBFN, and has potential for compact realization by means of full integration on chip. The impact of the optical beamformer concept on the performance of the full receiver system is analyzed, by modeling the combination of the PAA and the beamformer as an equivalent two-port RF system. The results are illustrated by a numerical example of a PAA receiver for satellite TV reception, showing that - when properly designed - the beamformer hardly affects the sensitivity of the receiver.

Novel Ring Resonator-Based Integrated Photonic Beamformer for Broadband Phased Array Receive Antennas—Part II: Experimental Prototype

An experimental prototype is presented that illustrates the implementation aspects and feasibility of the novel ring resonator-based optical beamformer concept that has been developed and analyzed in Part I of this paper . This concept can be used for seamless control of the reception angle in broadband wireless receivers employing a large phased array antenna (PAA). The design, fabrication, and characterization of a dedicated chip are described, in which an 8 × 1 optical beamforming network, an optical sideband filter for single-sideband suppressed carrier modulation, and a carrier re-insertion coupler for balanced optical detection are integrated. The chip was designed for satellite television reception using a broadband PAA, and was realized in a low-loss, CMOS-compatible optical waveguide technology. Tuning is performed thermo-optically, with a switching time of 1 ms. Group delay response and power response measurements show the correct operation of the OBFN and OSBF, respectively. Measurements on a complete beamformer prototype (including the electro-optical and opto-electrical conversions) demonstrate an optical sideband suppression of 25 dB, RF-to-RF delay generation up to 0.63 ns with a phase accuracy better than ¿/10 radians, and coherent combining of four RF input signals, all in a frequency range of 1-2 GHz.

Spectrally efficient optical label insertion/extraction technique using an optical single sideband filter

A novel label insertion technique, using an adaptive optical single sideband (OSSB) filter, is experimentally shown. The OSSB filter is used to suppress one of the sidebands of the 40-Gb/s payload signal, and a 2.5-Gb/s intensity modulated signal is inserted as a label in the suppressed sideband. Lower label-payload crosstalk is observed using the OSSB filter compared to the absence of sideband suppression, allowing a reduction of 5 dB in the label power without additional penalty. The enhanced tolerance to group velocity dispersion (GVD) of the payload is experimentally assessed and a 5-dB penalty is observed for 136 ps/nm of accumulated dispersion. Additionally, simulation results show the efficient use of electrical dispersion compensation to improve the GVD tolerance, allowing the doubling of the dispersion tolerance

CATV/radio-on-fiber transport system based on direct modulation

A directly modulated CATV/radio-on-fiber (ROF) transport system based on external light injection technique, optical single sideband (SSB) filter, and RF amplifier predistorter is proposed and demonstrated. To the best of my knowledge, it is the first time to transmit CATV and ROF signals simultaneously in a directly modulated form. Good performances of carrier-to-noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) were obtained for CATV band; and low third order intermodulation distortion to carrier ratio (IMD3/C), and bit error rate (BER) values were achieved for ROF application.

A comparison between optical SSB transmitter/filter in a full-duplex radio-on-fiber transport system

We present the investigation of the fiber Bragg grating (FBG) filter as an optical single sideband (SSB) filter at the receiving site. A comparison is made with an alternative optical SSB generation technique using optical SSB transmitter. The function of the optical SSB filter is employed to replace the optical SSB transmitter, not only to select the appropriate wavelength but also to suppress the fiber dispersion effect. Using simple FBG filter as an optical SSB filter in full-duplex radio-on-fiber (ROF) transport systems is a very attractive option, as it is passive and potentially low cost.

CSO/CTB Performances Improvement by Using Optical SSB Filter at the Receiving Site

We propose and demonstrate an externally modulated national television system committee (NTSC) 77-channel erbium-doped fiber amplifier-repeated system employing an optical single sideband filter at the receiving site. In comparison with conventional externally modulated fiber-optical CATV systems, excellent performances of carrier-to-noise ratio /spl ges/50 dB, composite second order /spl ges/70 dB, and composite triple beat /spl ges/69 dB were achieved for the full channel band over a 100-km single-mode fiber transport. Our proposed system is suitable for the long-haul fiber-optical CATV system.

Adaptive optical single sideband filter based on a phase modulator

A novel optical single sideband filter based on a phase modulator and electrical processing is proposed. Complete sideband suppression is theoretically achieved for intensity modulated carrier-unsuppressed optical signals with pulse shape transparency. Sideband suppression power ratio exceeding 15 dB is achieved for an optical non-return to zero signal using common electrical components.

Employing split-band technique and optical SSB filter to Improve directly modulated fiber optical CATV system performances

A directly modulated AM-VSB CATV EDFA-repeated system that uses split-band technique and optical single sideband (SSB) filter at the receiving site is proposed and demonstrated. Good performances of CNR, CSO and CTB were achieved for the full channel band over a-120km single-mode fiber (SMF) transport. Our proposed system is suitable for the fiber optical CATV systems in long-haul transport.

Photonic mm-Wave Generation Using a Double Passband Fiber Bragg Grating Filter

We report a simplified version of a mm-wave generator employing the sideband filtering technique which uses a single optical sideband filter. Instead of using a Mach-Zehnder-like fiber network to select a pair of sidebands, we employ a single Fabry-Perot fiber Bragg grating with a pair of passbands separated by the mm-wave frequency. Using a single filter eliminated the need for polarization control and pathlength matching that was required by the former interferometer-like arrangement. We describe a 30 GHz generator design and present its mm-wave signal spectrum showing an instrument-limited linewidth of ~20 Hz. The generation of such an extremely narrow signal spectrum from a laser with a 1 MHz linewidth demonstrates the remarkable laser frequency noise cancellation property of the sideband filtering technique.

Lightwave single sideband wavelength self-tunable filter using an InP:Fe crystal for fiber-wireless systems

A new optical single sideband filter is presented to compensate for chromatic dispersion effects in fiber-wireless systems. The device is based on three dynamic Bragg gratings, which are generated in a photorefractive iron-doped indium phosphide (InP:Fe) crystal. This filter is controlled by the input optical double sideband signal itself, which makes it independent of the modulated optical carrier wavelength. In this paper, the principle of the device is presented and demonstrated. Experiments include a 14-km fiber transmission followed by a 3-m radio link carrying a 140-Mb/s binary phase-shift keyed data stream at 16 GHz.

Fiber-optic millimeter-wave downlink system using 60 GHz-band external modulation

In this paper, a fiber-optic millimeter-wave (mm-wave) downlink system using 60 GHz-band external modulation is investigated. We prepare the fiber-optic 60 GHz-band mm-wave downlink testbed. It consists of an optical modulation section with a mm-wave signal generator, an optical single sideband (SSB) filter, a standard single-mode fiber (SMF), an optical detection section with a 60 GHz-band radio transmitter and a 60 GHz-band radio receiver. To modulate the laser output with 60 GHz-band mm-wave signals directly, a specially designed electro-absorption modulator with high-efficiency at around 60 GHz is used. The use of this modulator makes the simpler system configuration possible. Using the downlink testbed, the 5 m-long free-space propagation of subcarrier multiplexed 156 Mb/s-DPSK 60 GHz-band mm-wave signals recovered by optical direct detection is successfully demonstrated. The transmission of the mm-wave signals over 85 km-long standard SMF is also successfully demonstrated, using an optical SSB filtering technique to overcome the fiber dispersion. The BER of 10/sup -9/ is achievable at the optical received power of -7.0 dBm.