Recirculating Delay Line Research Articles

Stable and Widely Tunable Optoelectronic Oscillator Using a Cascade Microwave Photonic Filter

A widely tunable optoelectronic oscillator (OEO) with stable output based on a cascade microwave photonic filter (MPF) is proposed and demonstrated. The cascade MPF is implemented by a combination of a finite impulse response (FIR) filter based on shifted dispersion-induced power fading and an infinite impulse response (IIR) filter based on a double-parallel recirculating delay lines (DP-RDLs). Through adjusting the time delay difference between the upper and lower connecting arms of the dual-input Mach-Zehnder modulator within FIR filter, the center frequency of cascade MPF is changed and the oscillation frequency of the OEO can be tuned. The theoretical analysis and verified experiment of the proposed OEO is performed. Tunable oscillation signals from 6.1 to 11.98 GHz with an average step size of 490 MHz are generated. Due to the introduce of the IIR filter, the stable performance of the OEO is obtained, where the maximum frequency drift at 7.48 GHz is observed to be 1.817 kHz over 1 hour. The phase noise of the structure is also investigated

Suppression of Phase Induced Intensity Noise in Recirculating Delay Line Microwave Photonic Filters

High-Q microwave photonic filters may be realised with infinite impulse response (IIR) transfer functions, which are implemented typically with all-optical recirculating delay lines (RDL) operating in the incoherent regime. A key problem with these structures is phase-induced intensity noise (PIIN), which results in SNR degradation. Here we show that by using a hybrid optoelectronic loop instead of an all-optical loop for the RDL, it is possible to reduce the PIIN by up to 28 dB and to also achieve a higher finesse by letting the loop gain approach unity. The significance of the PIIN reduction is shown with the comparison of optoelectronic oscillators implemented with the all-optical RDL and the hybrid optoelectronic RDL, with the latter leading to a reduction in phase noise of 14 dB at 10 kHz frequency offset.

Wideband tunable optoelectronic oscillator based on a single-bandpass microwave photonic filter and a recirculating delay line

A wideband tunable optoelectronic oscillator (OEO) based on a tunable single-bandpass microwave photonic filter (MPF) and a recirculating delay line is proposed and experimentally demonstrated. The MPF is formed by cascading a finite impulse response filter and an infinite impulse response filter, which can enhance the quality factor of the MPF and suppress the side modes of the OEO. The frequency response of the tunable MPF is theoretically analyzed. By placing the MPF into the OEO, tunable microwave signals from 10.3 GHz to 26.7 GHz and a 100 MHz step tunability are experimentally demonstrated. The phase noise is −113 dBc/Hz@10 kHz. The results agree well with the theory.

Frequency-multiplying optoelectronic oscillator with a tunable frequency multiplication technique

An optoelectronic oscillator (OEO) for the generation of a frequency-doubled or -quadrupled microwave signal with a tunable frequency multiplication technique is proposed and demonstrated. In the proposed OEO, a modulated signal is generated by a Mach–Zehnder modulator (MZM). The modulated signal is then divided into two parts. One part is sent to a photodetector (PD1) via an optical domain dual-loop composite cavity and then fed back to the MZM to form the OEO loop that can generate an oscillation signal with the frequency determined by the center frequency of an electrical bandpass filter used in the loop and the length difference of the dual-loop composite cavity. The other part is sent to a fiber-optic recirculating delay line (RDL) structure and then applied to another PD (PD2) for the formation of a microwave photonic (MWP) notch filter. Through using the cascade characteristics of the RDL loop in the fiber-optic RDL structure and the notch response of the MWP notch filter, a frequency-doubled or -quadrupled microwave signal is generated. A detailed theoretical analysis is provided and the results are verified by an experiment. A fundamental oscillation signal at 5.592 GHz is generated in the OEO loop, which is multiplied to generate a frequency-doubled microwave signal at 11.184 GHz or a frequency-quadrupled microwave signal at 22.368 GHz, respectively. The performance of the generated microwave signals is also investigated.

High- $Q$ Optoelectronic Oscillator Based on Active Recirculating Delay Line and Dual-Loop Topology

A high Q-factor optoelectronic oscillator (OEO) based on an active recirculating delay line and a dual-loop topology is proposed and demonstrated experimentally. The implemented OEO provides a very stable oscillation at 5.4 GHz with a sub-Hz 3-dB bandwidth and a $Q$ -factor in excess of $10^{10}$ . A single side-band phase noise of −74 dBc/Hz is measured at 10 kHz offset, while side modes are significantly suppressed for offset values in the range of 100 kHz–1 MHz.

All-Optical Virtual Private Network in OFDM-PON Using Microwave Photonic Filter

We propose and demonstrate a novel all-optical virtual private network (VPN) using a microwave photonic filter, which enables inter-communications among optical network units in a passive optical network system. In our scheme, an optical coupler based recirculating delay line is used at optical line terminal as an optical subsystem to implement a microwave photonic-bandpass filter (MP-BPF). The periodic passbands of an MP-BPF are used to transmit VPN signal, whereas stopbands are used for conventional upstream transmission. The proposed system has two critical issues, optical phase-induced intensity noise in the MP-BPF and Rayleigh back-scattering interference by a single-fiber loop back link. To overcome the issues, an RF clipping tone based spectrum-broadening technique is applied to uplink transmitter. The proposed all-optical VPN system is tolerant to wavelength of VPN optical carrier, and enables multi-VPN data transmission using multi-passbands of MP-BPF.

Reconfigurable optoelectronic oscillator incorporating a double-coupling recirculating delay line

A reconfigurable optoelectronic oscillator (OEO) based on a double-coupling recirculating delay line (DC-RDL) is analyzed and experimentally demonstrated. In the proposed OEO, an incoherent two-tap microwave photonic filter is formed by an amplified spontaneous emission (ASE) source, a Mach–Zehnder modulator, a DC-RDL, and a polarization beam splitter (PBS) to realize selection of the oscillation mode. Specifically, the incoherence is implemented using an ASE broadband laser source and a DC-RDL, and the high sidemode suppression performance can be achieved by employing the dual-loops system between the dual output of the DC-RDL and the PBS. A detailed theoretical analysis is provided and is verified by the experiment. The single-sideband phase noise, the frequency tunability, and the long-term stability of the generated microwave signal are investigated. In addition, the frequency independent of the phase noise is also experimentally observed.

A Novel Optoelectronic Oscillator with Series-Coupled Double Recirculating Delay Lines

An optoelectronic oscillator (OEO) based on series-coupled double recirculating delay lines (SC-DRDLs) is analyzed and experimentally demonstrated. The SC-DRDLs composed by the coupling cascade of two RDLs, which the free spectral range (FSR) is least common multiple of the two RDLs’ FSR, and then the large FSR can be obtained by properly setting the loop lengths of two RDLs. By consociation with the dual loops system between the dual output of the SC-DRDLs and PBS, the high sidemode suppression performance can be achieved. Meantime, the incoherence of the SC-DRDLs can be performed by using an amplified spontaneous emission (ASE) broadband laser source. An experiment is carried out. A microwave signal with high spectral purity, long-term stability, low single-sideband (SSB) phase noise is generated.

Instantaneous high-resolution multiple-frequency measurement system based on frequency-to-time mapping technique

A new microwave photonic instantaneous frequency measurement system that can simultaneously measure multiple-frequency signals while achieving very high resolution and wide frequency measurement range is presented. It is based on the frequency-to-time mapping technique implemented using a frequency shifting recirculating delay line loop and a narrowband optical filter realized by the in-fiber stimulated Brillouin scattering effect. Experimental results demonstrate the realization of a multiple-frequency measurement capability over a frequency range of 0.1-20GHz that can be extended to 90GHz, and with a measurement resolution of 250MHz.

Photonic Radio Frequency Memory Using Frequency Shifting Recirculating Delay Line Structure

A new structure for storing a radio frequency (RF) signal utilising a fibre-optic delay line is presented. It is based on a frequency shifting recirculating delay line loop for the RF pulse storage, which prevents lasing and enables multiple recirculations and long storage time to be realised. The new photonic RF memory (PRFM) can realise a long reconfigurable storage time, wide instantaneous bandwidth and high dynamic range. Experimental demonstration of the frequency shifting loop based PRFM has been carried out for the first time, showing a long and reconfigurable storage time of more than 300 μs with high signal fidelity.

Switchable and tunable microwave photonic filter based on reflective semiconductor optical amplifier

ABSTRACTA microwave photonic filter, which can be switched between a high‐Q bandpass filter and a notch filter, is proposed and experimentally demonstrated. It is based on a recirculating delay line loop with a reflective semiconductor optical amplifier, and negative taps are generated employing wavelength conversion. The filter can be also tuned by adjusting an optical variable delay line. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:198–201, 2014

A new technique for 100-fold increase in the FSR of optical recirculating delay line filters using a time compression unit

A new technique that increases the free spectral range (FSR) of a recirculating delay line filter, is presented. The concept is based on a time-compression unit, which is used in conjunction with a frequency-shifting recirculating loop that generates multi-spectral characteristics, and the idea exploits the optical wavelength domain by wavelength-to-time mapping of the taps using an oppositely time-oriented dispersive element so that the taps travel different lengths, to time compress the tap separation. This technique solves, for the first time, the long-standing problem of the small FSR limitation in recirculating microwave photonic delay line filters, opening the way to realize the main functionalities required in microwave photonic filters. Experimental results are presented which demonstrate a large 100-fold increase in the FSR of the bandpass filter response.

Single sideband suppressed carrier modulator based frequency shifting recirculating delay line microwave photonic filter

A high-resolution low-noise single-laser photonic filter that can operate to high frequencies is presented. It is based on the single-sideband suppressed carrier electro-optic modulator frequency shifter that enables high frequency shifts to be realised in a frequency shifting amplified recirculating delay line loop structure. Designs to minimise the unwanted spurious harmonic frequencies generated by the single-sideband suppressed carrier modulator are presented. Simulations are presented to investigate the gain spectrum limitations that arise from the bandwidth narrowing of the erbium-doped fibre amplifier due to the important self-filtering effects that occur when the signals circulate inside the frequency shifting amplified recirculating delay line loop, and new techniques to counter this effect and to realise a large number of taps is presented. Experimental results demonstrate a high-resolution microwave photonic filter with a Q of 107 and with low-noise performance.

A reconfigurable optoelectronic oscillator based on cascaded coherence-controllable recirculating delay lines

A novel optoelectronic oscillator (OEO) using cascaded recirculating delay lines (RDLs) is proposed and experimentally demonstrated. In the proposed OEO, instead of the use of an electronic microwave ðlter, two infinite impulse response (IIR) photonic microwave ðlters (PMFs) formed by two RDLs are employed to select oscillation frequencies. Specifically, an amplified spontaneous emission (ASE) source is adopted to avoid self-interference of each RDL, and two approximately equal gain RDLs are employed to reduce the influence of mutual interference between the two RDLs. Therefore, a stable microwave signal can be generated from the OEO loop. In the experiment, by tuning the lengths of RDLs, microwave signals at different frequencies, such as 194.1MHz, 648.5MHz and 2.99GHz, have been generated. The phase noise performance of the generated microwave signal is also investigated. The proposed approach has the potential for the generation of microwave signals up to tens of GHz with the use of integrated micro-ring devices.

High-Resolution Tunable RF/Microwave Photonic Notch Filter With Low-Noise Performance

A new high-resolution tunable RF/microwave photonic notch filter with low-noise performance is presented. It is based on using a dual-input electro-optic intensity modulator together with a frequency-shifting amplified recirculating delay line loop. It can realize a very narrow notch, and also a wide and flat passband to simultaneously excise interference with minimal impact on the wanted signal. The notch filter can be integrated into optical fibre microwave transmission systems. Experimental results are presented which demonstrate a notch filter response with a very narrow notch width of 0.55% of the filter free spectral range, a wide and flat passband, and a high signal-to-noise ratio of 114 dB/Hz. The ability to tune the notch frequency of the filter is also demonstrated.

All-Optical Microwave Photonic Filter Based on Electrooptic Phase Modulator and Detuned Wavelength Division De-Multiplexer

We theoretically and experimentally investigate a microwave photonic filter with an electrooptic phase modulator and an array waveguide grating, which acts as a detuned two-channel wavelength division de-multiplexer. In the experiment, a microwave notch filter with a QN factor of 236 and a rejection ratio of 31 dB is obtained by introducing microwave subtraction directly in optical domain. The parameter QN factor is defined to measure the rejection selectivity of a microwave notch filter and corresponding to the Q factor in a microwave bandpass filter. A microwave bandpass filter with a Q factor of 245 and a rejection ratio of 38 dB is also obtained. The relationship between the Q factor of the microwave bandpass filter and the QN factor of the microwave notch filter is measured. The variations of Q and QN versus the detuning of the tunable optical bandpass filter (TOBF), which is incorporated in the recirculating delay line loop, is also measured and discussed. Simulation results about the influences of the wavelength division de-multiplexer and TOBF on the microwave frequency response are also presented and analyzed.

Coherence-free cascade IIR microwave photonic filter with high Q factor

A new high- Q infinite impulse response (IIR) microwave photonic filter is demonstrated, in which two active recirculating delay line loops based on a semiconductor optical amplifier (SOA) are cascaded. Due to cross-gain modulation in the SOA, interferences between light beams travelling along different paths are removed, ensuring stable operation and linearity of the electrical transfer function. The whole transfer function comprises a term representing a cascade response of two IIR filters, which significantly increases the free spectral range and the Q factor. The filter exhibits a Q factor of 1870 with a rejection ratio of 25 dB.

Cascaded Multiple Infinite Impulse Response Optical Delay Line Signal Processor Without Coherent Interference

A technique that enables two or more infinite impulse response optical delay lines to be connected in series without the coherent interference problem is presented. It is based on inserting an optical frequency shifter into the infinite impulse response optical delay line structure. Signal processors based on the cascaded optical delay line structure have a higher frequency response performance than the single optical delay line structure. Experimental results are presented, which demonstrate a dual series frequency shifting amplified recirculating delay line can realise a high-resolution, high skirt selectivity, high stopband rejection level bandpass filter response, and a narrow-passband, flat-top bandpass filter response using a non-commensurate delay line approach.

High-Q frequency shifting recirculating delay line bandpass photonic filter

An all-optical photonic bandpass filter which achieves a very high-Q performance while simultaneously exhibiting low noise operation, is presented. It can generate a large number of taps without the problem of lasing thus enabling the realisation of high-resolution bandpass filtering. Experimental results for a photonic filter demonstrate a Q factor of 407, together with low noise and a stopband rejection of 50 dB. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1284–1286, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26011

All-Optical Microwave Filter With High Frequency Selectivity Based on Semiconductor Optical Amplifier and Optical Filter

We propose and experimentally demonstrate a novel all-optical microwave filter with high frequency selectivity. It is based on a recirculating delay line (RDL) loop in which a semiconductor optical amplifier (SOA) is followed by a tunable narrowband optical filter and a 1 × 2 10:90 optical coupler. Converted signal used as a negative tap is generated through wavelength conversion employing the cross-gain modulation (XGM) of the amplified spontaneous emission (ASE) spectrum of the SOA. The converted signal circulating in the RDL loop can realize a high quality factor (Q) response after photo-detection. The 1 × 2 10:90 coupler is employed to extract 10% optical power from the loop as output. A frequency response with a high Q factor of 543, a rejection ratio of 40 dB and a shape factor of 15.4 is experimentally demonstrated.