We experimentally investigate the synchronous response of two fiber-optic coupled optoelectronic circuit oscillators based on resonant tunneling diodes (RTDs). The fiber-optic synchronization link employs injection of a periodic oscillating optical modulated signal generated by a master RTD-laser diode (LD) oscillator to a slave RTD-photodetector (PD) oscillator. The synchronous regimes were evaluated as a function of frequency detuning and optical injection strength. The results show the slave RTD-PD oscillator follows the frequency and noise characteristics of the master RTD-LD oscillator resulting in two oscillators with similar phase noise characteristics exhibiting single side band phase noise levels below -100 dBc/Hz at 1 MHz offset from the carrier frequency. Optical synchronization of RTD-based optoelectronic circuit oscillators have many applications spanning from sensing, to microwave generation, and data transmission.
With non-invasive properties and high sensitivities, portable optical biosensors are extremely desirable for point-of-care (POC) applications. Lab-on-a-chip technology such as microfluidics has been treated as an ideal approach to integrate complex sample processing and analysis units with optical detection elements. The work in this paper has developed an integrated dispersive component in combination with a microfluidic chip, providing a portable and inexpensive platform for on-chip spectroscopic sensing. We demonstrate an integrated microfluidic spectroscopic sensor by using an arrayed waveguide grating (AWG) device. In particular, a visible AWG device (λc=680nm) with chip size of 12.1mm by 1.5mm was designed and fabricated by employing flamed hydrolysis deposited (FHD) silica as the waveguide material. A straight input waveguide is used to perform device characterization while a perpendicular curved waveguide is employed to introduce laser excitation light. A polymer microfluidic chip is integrated with the AWG device by oxygen plasma bonding. To prove effectiveness of the integrated spectroscopic sensor, fluorescence spectrum of an organic fluorophore (Cy5) was tested. Reconstructed spectrum by using the AWG device is compared with the outcome from a conventional spectrometer and a good consistency is presented.
Presently, among the most demanding applications for highly sensitive magnetometers are Magnetocardiography (MCG) and Magnetoencephalography (MEG), where sensitivities of around 1pT.Hz-1/2 and 1fT.Hz-1/2 are required. Cryogenic Superconducting Quantum Interference Devices (SQUIDs) are currently used as the magnetometers. However, there has been some recent work on replacing these devices with magnetometers based on atomic spectroscopy and operating at room temperature. There are demonstrations of MCG and MEG signals measured using atomic spectroscopy These atomic magnetometers are based on chip-scale microfabricated components. In this paper we discuss the prospects of using photonic crystal optical fibres or hollow core fibres (HCFs) loaded with Rb vapour in atomic magnetometer systems. We also consider new components for magnetometers based on mode-locked semiconductor lasers for measuring magnetic field via coherent population trapping (CPT) in Rb loaded HCFs.
We investigate optoelectronic oscillator (OEO) configurations based on a laser diode driven by resonant tunnelling diode
(RTD) optical waveguide photo-detector (PD) oscillators, with an optical fiber feedback loop carrying a fraction of the
laser diode optical output that is re-injected into the OEO through the optical waveguide of the RTD-PD. In the
configurations reported here, we take advantage of the RTD negative differential resistance to provide electrical highbandwidth.
The optical fiber loop acts as a high quality optical energy storage element with low transmission loss. The
RTD based OEO can produces stable and low-phase noise microwave signals with attractive applications in photonics
and communication systems, mainly in fiber-optic based communication links since the RTD-OEO can be accessed both
optically and electrically.
Optoelectronic oscillators can provide low noise oscillators at radio frequencies in the 0.5-40 GHz range and in this
paper we review two recently introduced approaches to optoelectronic oscillators. Both approaches use an optical fibre
feedback loop. One approach is based on passively modelocked laser diodes and in a 40 GHz oscillator achieves up to 30
dB noise reduction. The other approach is based on resonant tunneling diode optoelectronic devices and in a 1.4 GHz
oscillator can achieve up to 30 dB noise reduction.
We present a review of Resonant Tunneling Diode (RTD) OptoElectronic Integrated Circuits (OEICs). Resonant
tunneling diodes (RTDs) can be relatively easily integrated on the same chip as optoelectronic components and in this
paper we discuss the integration of RTDs with laser diodes, electroabsorption modulators and photodiodes. The RTD
provides the OEIC with negative differential resistance over a wide bandwidth. RTDs are highly nonlinear devices and
by applying nonlinear dynamics we have recently gained considerable insight into the operation of the RTD OEICS and
that has allowed us to design, fabricate and characterize OEICs for wireless/photonic interfaces.
Recent work on an OptoElectronic Integrated Circuit (OEIC), the resonant tunneling diode-laser diode (RTD-LD) has
shown that it can act as an optoelectronic voltage controlled oscillator (OVCO). The RTD-LD oscillates because of the
negative differential resistance of the RTD and simply providing the RTD-LD with a dc voltage will cause it to oscillate
at frequencies determined by both the external components of the circuit and the value of the dc voltage. It has been
observed to oscillate at frequencies as high as 2.2GHz and be tunable from 1.8-2.2GHz as the dc voltage is tuned by
0.5V. Both monolithic and hybrid (separate RTD and LD chips) have been investigated. The hybrid RTD-LD has been
accurately modeled as a Liénard's oscillator - closely related to the Van der Pol oscillator. The model is a classic of
nonlinear systems theory and explains all of the observed operating features that include synchronization and chaotic
output. Applications include wireless to optical signal conversion where phase synchronization has been demonstrated to
transfer phase modulated signals from the wireless to the optical domain by modulating the RTD-LD OVCO to produce
a phase modulated optical sub-carrier.
Photonic devices that exploit photonic crystal (PhC) principles in a planar environment continue to provide a fertile field of research. 2D PhC based channel waveguides can provide both strong confinement and controlled dispersion behaviour. In conjunction with, for instance, various electro-optic, thermo-optic and other effects, a range of device functionality is accessible in very compact PhC channel-guide devices that offer the potential for high-density integration. Low enough propagation losses are now being obtained with photonic crystal channel-guide structures that their use in real applications has become plausible. Photonic wires (PhWs) can also provide strong confinement and low propagation losses. Bragg-gratings imposed on photonic wires can provide dispersion and frequency selection in device structures that are intrinsically simpler than 2D PhC channel guides--and can compete with them under realistic conditions.
Semiconductors and in particular AlGaAs operated at photon energies below half the band gap have proven over the last few years to be optimum materials for studying nonlinear guided phenomena, including ultrafast all-optical switching. Here we report experimental results on a range of characterization measurements and implementations of all-optical switching devices.
Recent progress in guided-wave lasers and quasi-phase-matched (QPM) second harmonic generation (SHG) devices fabricated in lithium niobate and lithium tantalate will be reviewed. Significant new results from research carried out by us will also be presented. Relevant aspects of the proton exchange waveguide formation process will be examined. Because of the major limitations encountered so far with lithium niobate and tantalate, alternative materials with potentially superior properties should be considered and these are touched on at the end of the paper.