Bandwidth requirements continue to drive the need for low-power, high speed interconnects. Harnessing the mature CMOS technology for high volume manufacturing, Silicon Photonics is a top candidate for providing a viable solution for high bandwidth, low cost, low power, and high packing density, optical interconnects. The major drawback of silicon, however, is that it is an indirect bandgap material, and thus cannot produce coherent light. Consequently, different integration schemes of III/V materials on silicon are being explored. An integrated CMOS tunable laser is demonstrated as part of a composite-CMOS integration platform that enables high bandwidth optical interconnects. The integration platform embeds III-V into silicon chips using a metal bonding technique that provides low thermal resistance and avoids lattice mismatch problems. The performance of the laser including side mode suppression ratio, relative intensity noise, and linewidth is summarized.
Whispering-Gallery-Mode (WGM) resonators are emerging as an excellent platform to study optical phenomena resulting from enhanced light-matter interactions due to their superior capability to confine photons for extended periods of time. The monolithic fabrication process to achieve ultra-high-Q WGM resonators without the need to align multiple optical components, as needed in traditional design of resonators based on precise arrangement of mirrors, is especially attractive. Here we explain how to process a layer of thin film doped with optical gain medium, which is prepared by wet chemical synthesis, into WGM structures on silicon wafer to achieve arrays of ultra-low threshold on-chip microlasers. We can adjust the dopant species and concentration easily by tailoring the chemical compositions in the precursor solution. Lasing in different spectral windows from visible to infrared was observed in the experiments. In particular, we investigated nanoparticle sensing applications of the on-chip WGM microlasers by taking advantages of the narrow linewidths and the splitting of lasing modes arising from their interactions with nano-scale structures. It has been found that a nanoparticle as small as ten nanometers in radius could split a lasing mode in a WGM resonator into two spectrally separated lasing lines. Subsequently, when these lasing lines are photo-mixed at a photodetector a heterodyne beat note is generated which can be processed to signal the detection of individual nanoparticles. We have demonstrated detection of virions, dielectric and metallic nanoparticles by monitoring the changes in this self-heterodyning beat note of the split lasing modes. The built-in self-heterodyne method achieved in this monolithic WGM microlaser provides an ultrasensitive scheme for detecting and measuring nanoparticles at single particle resolution, with a theoretical detection limit of one nanometer.
Whispering-Gallery-Mode (WGM) microresonators have shown great promise for ultra-sensitive and label-free chemical
and biological sensing. The linewidth of a resonant mode determines the smallest resolvable changes in the WGM
spectrum, which, in turn, affects the detection limit. The fundamental limit is set by the linewidth of the resonant mode
due to material absorption induced photon loss. We report a real-time detection method with single nanoparticle
resolution that surpasses the detection limit of most passive micro/nano photonic resonant devices. This is achieved by
using an on-chip WGM microcavity laser as the sensing element, whose linewidth is much narrower than its passive
counterpart due to optical gain in the resonant lasing mode. In this microlaser based sensing platform, the first binding
nanoparticle induces splitting of the lasing line, and the subsequent particles alter the amount of splitting, which can be
monitored by measuring the beat frequency of the split modes. We demonstrate detection of polystyrene and gold
nanoparticles as small as 15 nm and 10 nm in radius, respectively, and Influenza A virions. The built-in self-heterodyne
interferometric method achieved in the monolithic microlaser provides a self-referencing scheme with extraordinary
sensitivity, and paves the way for detection and spectroscopy of nano-scale objects using micro/nano lasers.
Ultra-sensitive and label-free chemical and biological sensing devices are of great importance to biomedical research,
clinical diagnostics, environmental monitoring, and homeland security applications. Optical sensors based on ultra-highquality
Whispering-Gallery-Mode (WGM) micro-resonators, in which light-matter interactions are significantly
enhanced, have shown great promise in achieving compact sensors with high sensitivity and reliability. However,
traditional sensing mechanisms based on monitoring the frequency shift of a single resonance faces challenges since the
resonant frequency is sensitive not only to the sensing targets but also to many types of disturbances in the environment,
such as temperature variation and mechanical instability of the system. The analysis of the signals is also affected by the
positions of sensing targets on the resonator. Thus, it is difficult to distinguish signals coming from different sources,
which introduces 'false positive' detection. We report a novel self-reference sensing mechanism based on mode splitting,
a phenomenon in which a high-quality optical mode in a WGM resonator splits into two modes due to intra-cavity
Rayleigh scattering. In particular, we demonstrated that the two split modes that can be induced by a single nanoparticle
reside in the same resonator and serve as a reference to each other. As a result, a self-reference sensing scheme is
formed. This allows us to develop a position-independent sensing scheme to accurately estimate the sizes of
nanoparticles. So far we have achieved position-independent detecting and sizing of single nanoparticles down to 20 nm
in radius with a single-shot measurement using an on-chip high-quality WGM microtoroid resonator.
Optical microcavities with high quality factors (Q factor) and small mode volumes have shown their potentials in various
sensing applications. Here we experimentally demonstrate the real-time detection of single nanoparticles down to 30 nm
in radius, using an ultra-high-Q microtoroid on a silicon chip. Mode splitting phenomenon of WGMs caused by their
strong interactions with a single nanoparticle is utilized as the sensing signal. Frequency and linewidth information of
the split modes is used to accurately derive the size of the particle detected. Theoretical calculations and finite element
simulations are in good agreement with the experimental results. The mode splitting technique provides a self-reference
scheme that is more immune to noise than the techniques based on the detection of changes of a single mode.
Whispering gallery mode (WGM) optical microcavities trap light in micro-scale volumes by continuous total internal
reflection which leads to enhancement of light intensity within a confined region and longer photon lifetime.
Consequently, light-matter interaction is enhanced making the WGM resonator an extremely sensitive platform for the
detection of perturbations in and around the resonator. Here, we report mode-splitting in monolithic ultra-high-Q WGM
microcavities for real-time and in-situ detection of single nanoparticles. We investigate experimentally and theoretically
particle detection and sizing at single nanoparticle resolution using the mode-splitting technique. Theoretical calculations
are in good agreement with the experimental results. The mode-splitting effect provides a 'self-reference sensing'
technique that can overcome the limitations of current resonator-based sensors and in the meantime keep the advantages
offered by resonant structures for high-performance sensing.
A remnant chromatic dispersion monitoring method based on spectral shift of a semiconductor optical amplifier is proposed for a high speed optical communication system with carrier suppressed return to zero format and single-channel speed of 40 Gbit/s. The monitoring performance can be optimized by carefully selecting the bandwidth and center wavelength of the optical filter. The dynamical monitoring range is ±60 ps/nm and the monitoring precision is about 5 ps/nm. This method is suitable for application in dynamical chromatic dispersion compensation of high speed optical communication systems.
A chirped, phase-shifted structure is demonstrated for compact multi-wavelength DFB fiber laser at room temperature for the first time. The chirped structure provides separated resonance cavities and then the stable multi-wavelength operation. The equivalent phase shift method is demonstrated to realize the desired chirp and phase shifts simply and flexibly. A 44pm-spaced, dual-wavelength DFB fiber laser is then achieved experimentally, which is the narrowest spacing ever reported for a compact multi-wavelength fiber laser.
We have developed a thermally tunable module to compensate polarization mode dispersion (PMD) and chromatic dispersion (CD) simultaneously. In this module, twins of linearly chirped fiber Bragg gratings (LCFBGs) are used to compensate PMD and one non-linearly chirped FBG (NLCFBG) is used to compensate CD in 40Gb/s optical fiber communication system. The fiber Bragg gratings are coated with uniform thin metal film, and by changing the applied current through the film, the tunable compensation for PMD and CD is achieved. The fabrications of the LCFBG and NLCFBG are both utilizing the linearly chirped phase mask, making the fiber Bragg gratings easy to obtain.
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