Jintong Lin

Broadband Photonic RF Channelization Based on Coherent Optical Frequency Combs and I/Q Demodulators

In this paper, a novel photonic-assisted broadband and high-resolution radio-frequency (RF) channelization scheme based on dual coherent optical frequency combs (OFCs), regular optical de-muxes, and I/Q demodulators is analyzed and experimentally demonstrated. The use of two coherent combs avoids precise optical alignment, and a numerical filter in digital signal processor (DSP) enables an ideal rectangular frequency response in each channel without any ultranarrow optical filters. Besides, due to the use of I/Q demodulators, ambiguous frequency estimate in direct detection is avoided. By using two coherent OFCs with the free spectrum range (FSR) of about 40 GHz, we experimentally demonstrate the channelization scheme with seven channels, 500-MHz channel spacing, and frequency coverage from 3.75 to 7.25 GHz. The input RF tones are accurately downconverted to an intermediate frequency (IF) with a maximum frequency error of 125 kHz. Meanwhile, the channel frequency response and crosstalk of the scheme are also evaluated experimentally.

UWB Pulse Generation and Distribution Using a NOLM Based Optical Switch

An approach is proposed in this paper to generate ultra-wideband (UWB) pulses based on cross-phase modulation (XPM) effects in nonlinear optical loop mirror (NOLM). The NOLM can be considered as an optical switch which is controlled by pump to generate positive and negative Gaussian pulses, which are then delayed by SMF and combined to generate both Gaussian monocycle and doublet pulses. These two pulse shapes can be switched at a high speed by controlling the on-off of one of the probe. In addition, the SMF acting as a chromatic dispersion media in generating the UWB pulses can also be used to distribute the UWB signals from the central station (CS) to remote access points (AP). Different distance between CS and remote APs has no effects on the generated UWB pulses by adopting a wavelength tunable laser as probe.

Broadband Photonic Radio-Frequency Channelization Based on a 39-GHz Optical Frequency Comb

A novel photonic channelization scheme for a wideband radio-frequency (RF) signal based on an optical frequency comb (OFC), a comb filter, and an optical de-mux is proposed and demonstrated. In the proposed channelizer, the input broadband RF signal is multicast by the OFC, spectrally sliced by a Fabry-Perot filter (FPF) and then channelized by a regular optical de-mux. Compared to previous proposals, the OFC can provide uniform and low-noise channelization and simplify the spectral alignment to the FPF. We demonstrate our scheme experimentally based on a 39-GHz-spaced OFC. As an application, instantaneous multiple-frequency measurement is demonstrated by directly detecting the channelized RF signal.

Enhanced Spurious-Free Dynamic Range in Intensity-Modulated Analog Photonic Link Using Digital Postprocessing

In this paper, a post digital linearization technique is proposed and demonstrated for a conventional intensity-modulation direct-detection analog photonic link. Instead of precisely emulating the transfer function of the whole nonlinear system in the digital domain, the key distortion information is directly acquired from hardware. By low biasing the Mach-Zehnder modulator, linearization can be achieved through simply multiplying the distorted signal by the coreceived low-pass band. Theory analysis shows that only the bias angle should be known by the algorithm, whereas the simulation shows adequate tolerance. The low bias angle also results in an improved link gain. The experiment shows a well-suppressed third-order intermodulation distortion (IMD3). With the optical down conversion, we demonstrate a spurious-free dynamic range increasing from 103.2 to 123.3 dB in a 1-Hz bandwidth.

Overcoming Chromatic-Dispersion-Induced Power Fading in ROF Links Employing Parallel Modulators

This letter presents a chromatic dispersion (CD) compensation scheme using parallel electro-optic phase and intensity modulators suitable for long-reach radio-over-fiber links. By properly adjusting the optical power and the time delay between the two modulated signals, the power fading aroused by the CD is adequately compensated over a wide operating bandwidth of 0-18 GHz over a 34-km single-mode fiber (SMF). Compared with a double sideband (DSB) modulated link, an enhancement of up to 31 dB·Hz2/3 in the spur-free dynamic range for a 9.5-GHz signal is obtained. Furthermore, a bit-error rate of 10-10 is obtained when a 9.5-GHz carrier loading 2-Gb/s pseudorandom bit sequence is transmitted over the dispersive link, which is not achievable for the DSB modulated link.

A Simple Photonic-Assisted Microwave Frequency Measurement System Based on MZI With Tunable Measurement Range and High Resolution

A simple and practical photonic approach for microwave instantaneous frequency measurement has been proposed and experimentally demonstrated. The unknown microwave signal with its frequency to be measured is carrier-suppressed modulated on the lightwave by a Mach-Zehnder modulator biased at the minimum point. And thanks to the inherent complementary transmission responses of the Mach-Zehnder interferometer (MZI), the fixed relationship between the amplitude comparison function and microwave frequency to be measured is established. By monitoring and processing the optical powers of the two output ports of the MZI, the frequency of the microwave signal could be easily estimated. The proposed scheme is experimentally verified and has many advantages, such as simple structure, low cost, fast response, practical prospect, tunable measurement range, and high resolution.

Photonic Polarity-Switchable Ultra-Wideband Pulse Generation Using a Tunable Sagnac Interferometer Comb Filter

A photonic approach to polarity-switchable ultra-wideband (UWB) pulse generation is proposed. The proposed setup principally consists of an electrooptic phase modulator (EOPM) and a tunable optical comb filter constructed with another EOPM inside a Sagnac interferometer. The comb filter working at its linear region performs the phase-to-intensity conversion to generate UWB pulses with monocycle shape. By adjusting the bias voltage of the EOPM inside the Sagnac interferometer, a shift of the comb filter can be achieved, which is the key point for a pulse polarity switch. A pair of monocycle pulses with reversed polarities was experimentally obtained by applying the dc bias of 0 and 1.9 V, respectively. The convenience to electrically control the pulse polarity is favorable for biphase modulation in UWB impulse radio applications.

All-Optical Logic or Gate Exploiting Nonlinear Polarization Rotation in an SOA and Red-Shifted Sideband Filtering

An all-optical logic or gate is presented by exploiting nonlinear polarization rotation (NPR) in a semiconductor optical amplifier (SOA) and red-shifted sideband filtering (NPR-RF). The logic or gate is successfully experimentally demonstrated with a 27-1 return-to-zero pseudorandom binary sequence at 20 Gb/s. The logic or gate is also successfully simulated, and dependence of signal quality Q-factor and extinction ratio on input signal power for several detuning is also simulated and discussed. The simulation results show high Q-factor can be achieved in strong saturation of SOA. The logic gate has a simple configuration and allows photonic integration

Integrated Multifrequency Recognition and Downconversion Based on Photonics-Assisted Compressive Sampling

On the basis of photonics-assisted compressive sampling (CS), we demonstrate for the first time an integrated system with the capacity of multifrequency recognition and downconversion of intercepted radio frequency (RF) component. Using a single analog-to-digital converter (ADC) with sub-Nyquist analog bandwidth of 826.75 MHz, a multicomponent signal with unknown frequencies ranging from 15 to 20 GHz is precisely located with maximum detection error of 100 kHz. The systems ability of photonic downconversion of identified RF component is characterized in terms of spur-free dynamic range (SFDR) as well.

Enabling ROF Technologies and Integration Architectures for In-Building Optical–Wireless Access Networks

This work presents our recent progress on advanced radio-over-fiber (ROF) technologies for in-building optical-wireless access networks, including multiservice, full-duplex, and polarization diversity ROF system design, as well as the experimental delivery of uncompressed high-definition television (HDTV) signals. The novel polarization diversity technique is proposed to improve receiving sensitivity and increase the anti-interference capacity of the wireless transmission at the in-building environment. Furthermore, the integration architecture of ROF and Ethernet passive optical network (EPON) is investigated, mainly focusing on polar duplex antenna for non-line-of-sight (NLOS) transmission and home gateway for different network topologies. The hybrid system distributes the multimedia services (e.g., HDTV in EPON) and other wireless data services to the terminal rooms over ROF links and thus expands the superbroadband EPON services to the subscribers for the last meters in both wired and wireless ways.