Surface plasmon resonance has established itself as an immensely acclaimed and influential optical sensing tool with quintessential applications in life sciences, environmental monitoring, clinical diagnostics, pharmaceutical developments and ensuring food safety. The implementation of sensing principle of surface plasmon resonance employing an optical fiber as a substrate has concomitantly resulted in the evolution of fiber optic surface plasmon resonance as an exceptionally lucrative scaffold for chemical and biosensing applications. This perspective article outlines the contemporary studies on fiber optic sensors founded on the sensing architecture of propagating as well as localized surface plasmon resonance. An in-depth review of the prevalent analytical and surface chemical tactics involved in configuring the sensing layer over an optical fiber for the detection of various chemical and biological entities is presented. The involvement of nanomaterials as a strategic approach to enhance the sensor sensitivity is furnished concurrently providing an insight into the diverse geometrical blueprints for designing fiber optic sensing probes. Representative examples from the literature are discussed to appreciate the latest advancements in this potentially valuable research avenue. The article concludes by identifying some of the key challenges and exploring the opportunities for expanding the scope and impact of surface plasmon resonance based fiber optic sensors.

[INVITED] Recent advances in surface plasmon resonance based fiber optic chemical and biosensors utilizing bulk and nanostructures

Time-delayed optoelectronic oscillators are at the center of a large body of scientific literature. The complex behavior of these nonlinear oscillators has been thoroughly explored both theoretically and experimentally, leading to a better understanding of their dynamical properties. Beyond fundamental research, these systems have also inspired a wide and diverse set of applications, such as optical chaos communications, pseudorandom number generation, optoelectronic machine learning based on reservoir computing, ultrapure microwave generation, optical pulse-train synthesis, and sensing. The aim of this review is to provide a comprehensive survey of this field, to outline the latest achievements, and discuss the main challenges ahead.

Optoelectronic oscillators with time-delayed feedback

With the rapid development of the modern communication systems, radar and wireless services, microwave signal with high-frequency, high-spectral-purity and frequency tunability as well as microwave generator with light weight, compact size, power-efficient and low cost are increasingly demanded. Integrated microwave photonics (IMWP) is regarded as a prospective way to meet these demands by hybridizing the microwave circuits and the photonics circuits on chip. In this article, we propose and experimentally demonstrate an integrated optoelectronic oscillator (IOEO). All of the devices needed in the optoelectronic oscillation loop circuit are monolithically integrated on chip within size of 5×6cm2. By tuning the injection current to 44 mA, the output frequency of the proposed IOEO is located at 7.30 GHz with phase noise value of −91 dBc/Hz@1MHz. When the injection current is increased to 65 mA, the output frequency can be changed to 8.87 GHz with phase noise value of −92 dBc/Hz@1MHz. Both of the oscillation frequency can be slightly tuned within 20 MHz around the center oscillation frequency by tuning the injection current. The method about improving the performance of IOEO is carefully discussed at the end of in this article.

Integrated optoelectronic oscillator.

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.

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

The optoelectronic oscillator (OEO) has attracted a great deal of attention in recent years as a high-performance microwave source. Thanks to the high quality-factor (Q-factor) provided by the optical delay line, the OEO can generate spectrally pure microwave signals with ultralow phase noise. Various approaches for realization of OEO architectures for the generation of single-frequency microwave signals have been demonstrated in the past two decades. Seeded by the microwave signal generated by OEO, the generation of complex microwave waveforms has been demonstrated, which can be used in applications such as radar and communication systems. OEO has also been demonstrated to perform other specific functionalities in different applications, including optical pulses and frequency comb generation, optical sensing, low-power microwave signal detection, and optical signal processing. This paper reviews the developments of OEO over the past two decades. An integrated OEO with monolithically integrated photonic parts and radio frequency subsections is reported as a promising example toward the monolithic integration of OEO. Key features of OEO and prospects for future development of the integration of OEO are also described.

Toward Monolithic Integration of OEOs: From Systems to Chips

A novel scheme to realize a low-cost and wideband frequency tunable optoelectronic oscillator based on a directly modulated distributed feedback (DFB) semiconductor laser is proposed and experimentally demonstrated. In the proposed scheme, neither an external modulator nor an electrical filter is used, and no more than 25 dB of the electrical loop gain is required due to the high modulation efficiency of the relaxation oscillation frequency of the DFB laser. Microwave signals with frequency coarsely tuned from 3.77 to 8.75 GHz are generated by changing the bias current and operation temperature of the DFB laser. The single sideband phase noise of the generated 6.97 GHz microwave signal is measured to be −103.6  dBc/Hz at 10 kHz offset.

Low-cost and wideband frequency tunable optoelectronic oscillator based on a directly modulated distributed feedback semiconductor laser.

A frequency tunable optoelectronic oscillator based on a directly modulated distributed-feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. Through optical injection, the relaxation oscillation frequency of the DFB laser is enhanced and its high modulation efficiency can enable the loop oscillation with a RF threshold gain of less than 20 dB. The DFB laser is a commercial semiconductor laser with a package of 10 GHz, and its packaging limitation can be overcome by optical injection. In our scheme, neither a high-speed external modulator nor an electrical bandpass filter is required, making the system simple and low-cost. Microwave signals with a frequency tuning range from 5.98 to 15.22 GHz are generated by adjusting the injection ratio and frequency detuning between the master and slave lasers. The phase noise of the generated 9.75 GHz microwave signal is measured to be -104.8 dBc/Hz @ 10 kHz frequency offset.

Frequency tunable optoelectronic oscillator based on a directly modulated DFB semiconductor laser under optical injection.

In this paper, a novel approach to realize a single passband microwave photonic filter (MPF) with wideband tunability based on an optical-injected distributed feedback (DFB) semiconductor laser is proposed and experimentally demonstrated The fundamental principle is based on the wavelength-selective amplification of the DFB laser under optical injection The frequency tunability, insertion loss, and out-of-band suppression ratio of the proposed MPF are investigated in the experiment By varying the injection locking parameters, MPFs with the frequency tuned from 11 to 41 GHz are achieved, and the insertion losses and out-of-band suppression ratios are around 20 dB They are useful in applications where high frequency and wideband tunability are required

A Novel Approach to Realizing a Widely Tunable Single Passband Microwave Photonic Filter Based on Optical Injection

A novel approach to realizing single sideband (SSB) modulation with optical carrier to sideband ratio (OCSR) of 0 dB, which is optimum for maximizing the transmission performance of a radio-over-fiber system, is proposed and experimentally demonstrated based on a strong optical injection-locked distributed feedback (DFB) laser. Tunable OCSR with optimum value of 0 dB is achieved by tuning the injection ratio and the detuning frequency precisely. A simulation is carried out to confirm the optimum OCSR. Gain properties of the DFB laser under strong optical injection are also measured for the first time to our knowledge. Doubled frequency of the LO signal is obtained without any filter. The generated optical SSB signal of 20 GHz is transmitted over 60-km single-mode fiber experimentally; results show it is almost not affected by the fiber chromatic dispersion.

A Novel Approach to Realizing SSB Modulation With Optimum Optical Carrier to Sideband Ratio

A wideband frequency-tunable optoelectronic oscillator using four-wave mixing nonlinear dynamics of an optical-injected distributed feedback (DFB) semiconductor laser is proposed and experimentally demonstrated. Utilizing the wavelength-selective optical gain of the DFB laser under optical injection, a frequency-tunable microwave photonic filter is realized, which is used as the desired oscillation frequency selector. Therefore, the electrical bandpass filter is not required in the proposed scheme. An optoelectronic oscillating signal with a frequency tuned from 9.63 to 19.11 GHz is obtained by changing the injection parameters. The single sideband phase noise of the generated 13.74-GHz microwave signal is measured to be −103.19 dBc/Hz at 10-kHz offset.

Jintian Xiong

Papers

Low-cost and wideband frequency tunable optoelectronic oscillator based on a directly modulated distributed feedback semiconductor laser.

Frequency tunable optoelectronic oscillator based on a directly modulated DFB semiconductor laser under optical injection.

A Novel Approach to Realizing a Widely Tunable Single Passband Microwave Photonic Filter Based on Optical Injection

A Novel Approach to Realizing SSB Modulation With Optimum Optical Carrier to Sideband Ratio

Tunable Optoelectronic Oscillator Using FWM Dynamics of an Optical-Injected DFB Laser