Femtosecond laser processing of microcavity lasers

In this paper, we reviewed the fabrications of functional microcavity lasers in soft materials such as polymer and protein by femtosecond laser processing. High-quality （Q） microdisks with a laser dye （Rhodamine B, RhB） acting as gain medium were fabricated that produced whispering-gallery-mode （WGM） lasing output. We also obtained unidirectional lasing output with a low lasing threshold in a deformed spiral microcavity at room temperature. Photonic-molecule （PM） microlasers were prepared to investigate the interaction and coupling effects of different cavities, and it was found that the distance between the two disks plays an important role in the lasing behaviors. Single-mode lasing was realized from a stacked PM microlaser through Vernier effect. Furthermore we adopted the biocompatible materials, RhB-doped proteins as a host material and fabricated a three-dimensional （3D） WGM microlaser, which operated well both in air and aqueous environment. The sensing of the protein micro- lasers to Na2SO4 concentration was investigated. Our results of fabricating high-Q microlasers with different materials reveal the potential applications of femtosecond laser processing in the areas of integrated optoelectronic and ultrahigh sensitive bio-sensing devices.

Universal single-mode lasing in fully chaotic two-dimensional microcavity lasers under continuous-wave operation with large pumping power [Invited]

For a fully chaotic two-dimensional(2D) microcavity laser, we present a theory that guarantees both the existence of a stable single-mode lasing state and the nonexistence of a stable multimode lasing state, under the assumptions that the cavity size is much larger than the wavelength and the external pumping power is sufficiently large. It is theoretically shown that these universal spectral characteristics arise from the synergistic effect of two different kinds of nonlinearities: deformation of the cavity shape and mode interaction due to a lasing medium. Our theory is based on the linear stability analysis of stationary states for the Maxwell–Bloch equations and accounts for single-mode lasing phenomena observed in real and numerical experiments of fully chaotic 2D microcavitylasers.

Electrically pumped metallic and plasmonic nanolasers

In recent years, there have been a significant number of demonstrations of small metallic and plasmonic lasers. The vast majority of these demonstrations have been for optically pumped devices. Electrically pumped devices are advantageous for applications and could demonstrate concepts not amenable for optical pumping. However, there have been relatively few demonstrations of electrically pumped small metal cavity lasers. This lack of results is due to the following reasons： there are limited types of electrically pumped gain media available; there is a significantly greater level of complexity required in the fabrication of electrically pumped devices; finally, the required components for electrical pumping restrict cavity design options and furthermore make it intrinsically more difficult to achieve lasing. This review looks at the motivation for electrically pumped nanolasers, the key issues that need addressing for them to be realized, the results that have been achieved so far including devices where lasing has not been achieved, and potential new directions that could be pursued.

Sensitivity to external optical feedback of circular-side hexagonal resonator microcavity laser

The sensitivity to fault reflection is very important for larger dynamic range in fiber fault detection technique.Using time delay signature(TDS)of chaotic laser formed by optical feedback can solve the sensitivity limitation of photodetector in fiber fault detection.The TDS corresponds to the feedback position and the fault reflection can be detected by the laser diode.The sensitivity to feedback level of circular-side hexagonal resonator(CSHR)microcavity laser is numerically simulated and the feedback level boundaries of each output dynamic state are demonstrated.The peak level of TDS is utilized to analyze the sensitivity.The demonstration is presented in two aspects:the minimum feedback level when the TDS emerges and the variation degree of TDS level on feedback level changing.The results show that the CSHR microcavity laser can respond to the feedback level of 0.07%,corresponding to-63-dB feedback strength.Compared to conventional distributed feedback laser,the sensitivity improves almost 20 dB due to the shorter internal cavity length of CSHR microcavity laser.Moreover,1%feedback level changing will induce 1.001 variation on TDS level,and this variation degree can be influenced by other critical internal parameters(active region side length,damping rate,and linewidth enhancement factor).

Mode characteristics of VCSELs with different shape and size oxidation apertures

Vertical cavity surface emitting laser(VCSELs)as the ideal light source for rubidium(Rb)and cesium(Cs)atomic clocks is analyzed for its mode and polarization control.We fabricated three kinds of shapes:triangular,elliptic,and circular oxidation apertures which also have different sizes.We formed three different shape oxide apertures by wetoxidation with 36μm-39μm circular mesa.Our results show that triangular oxidized-VCSEL has the advantages of mode and polarization selection over elliptic and circular oxide apertures.When triangular oxide-confined VCSELs emit in single mode,the measured side mode suppression ratio(SMSR)is larger than 20 d B and orthogonal polarization suppression ratio achieves 10 d B.Resonant blueshift of VCSELs with triangular and elliptic apertures is observed with the decrease of aperture size.

400 Gb/s physical random number generation based on deformed square self-chaotic lasers

A circular-sided square microcavity laser etched a central hole has achieved chaos operation with a bandwidth of 20.8 GHz without external optical feedback or injection,in which the intensity probability distribution of a chaotic signal with a twopeak pattern was observed.Based on the self-chaotic microlaser,physical random numbers at 400 Gb/s were generated by extracting the four least significant bits without other complex post-processing methods.The solitary chaos laser and minimal post-processing have predicted a simpler and low-cost on-chip random number generator in the future.

Polymeric photonic molecule super-mode lasers on silicon

Optically coupled microcavities have emerged as photonic structures with promising properties for investigation of fundamental science as well as for applications.We report on the fabrication and spatially resolved spectroscopy of on-chip photonic molecule(PM)lasers consisting of two coupled,dye-doped polymeric microdisks on a silicon substrate.We investigate the fundamental lasing properties with focus on the spatial distribution of modes,the coupling dependent suppression of lasing modes,and in particular the application-oriented operation of these devices in aqueous environments.By depositing an additional polymer layer onto the lithographically structured cavities made of dye-doped poly(methyl methacrylate),coupling-gap widths below 150 nm with aspect ratios of the micro-/nanostructure exceeding 9:1 are achieved.This enables strong optical coupling at visible wavelengths despite relatively small resonator radii of 25 μm.The lasing properties of dye-doped PMs are investigated using spatially resolved micro-photoluminescence(μ-PL)spectroscopy.This technique allows for the direct imaging of whispering-gallery modes(WGMs)in the photonics molecules.For subwavelength coupling gaps,we observe lasing from delocalized eigenstates of the PMs(termed in the following as super-modes).Using size-mismatched cavities,the lasing mode suppression for different coupling-gap widths is investigated.We further demonstrate single-mode lasing operation in aqueous environments with PMs,which are realized on a low-cost,polymer-on-silicon platform.

Light gain amplification in microcavity organic semiconductor laser diodes under electrical pumping

Organic semiconductor is one of the most promising luminescent and lasing materials that can be chemically synthesized with a controllable performance and possess high cross-section of stimulated emission[1].Organic semiconductor laser diodes(OSLDs)can be prepared by simple processing technologies and integrated easily with other optoelectronic devices.As a result,OSLDs would

Nanoparticle mediated microcavity random laser

This paper reports a coherent random microcavity laser that consists of a disordered cladding(scattering) layer and a light-amplification core filled with dye solution. Cold cavity analysis indicates that the random resonance modes supported by the proposed cavity can be effectively excited. With introducing the gain material, random lasing by specific modes is observed to show typical features of coherent random lasers, such as spatially incoherent emission of random modes. By inserting a metal nanoparticle into the gain region, emission wavelength/intensity of the random lasers can be considerably tuned by changing the position of the inserted nanoparticle,opening up new avenues for controlling output of random lasers and sensing applications(e.g., small particleidentification, location, etc.).

Printable microlaser arrays with programmable modes for information encryption

Lasing emissions with multiple and tunable modes are promising in coding field as a novel cryptographic primitive.With the advantages of simple fabrication,full-color and high-quality-factor whispering gallery mode lasing inside a circular cross-section,polymer microfibers are attractive for photonic devices.However,polymer lasing microfibers for information encryption have never been reported.Herein,we propose a design of printable lasing microfiber encryption chip by in-situ tuning the effective refractive index of the microresonator arrays via a facile approach.Through inkjet printing high-refractive-index nanoparticles on the designated position of lasing microfiber arrays,the effective refractive index of the microcavities is regulated,and the ratio of wavenumber spacing between transverse electric and transverse magnetic mode to the free spectral range can be modulated,particularly with neglectable influence by the size factor.Thus,the programmable region selective encoding process can be conducted simply by a printing program within several minutes.Besides,the encoded microfiber arrays are encapsulated into polydimethylsiloxane to reduce the scattering loss and environmental interference,and a printable encryption chip is realized.This work is expected to provide a platform for the printable encrypted devices.