Distributed Feedback Resonator Research Articles

Four‐Dimensional Design Space of High‐Q Second‐Order Distributed Feedback Perovskite Lasers

AbstractSecond‐order distributed feedback (DFB) resonators are widely used for thin‐film lasers as they combine low lasing thresholds with ease of manufacturing. Here, the grating design parameters are varied to map the lasing characteristics of lead halide perovskite films deposited on a single substrate that contains hundreds of high‐quality silicon nitride surface gratings. The lowest lasing threshold (≈130 µJ cm−2) is identified through the aid of near‐field and far‐field imaging spectroscopy in a four‐dimensional design space composed of grating period, duty cycle, active layer thickness, and cavity length. Moreover, it is shown that antisymmetric modes support high‐quality lasing (Q up to ≈10800) in the second‐order DFBs. The multi‐dimensional experimental analysis is accompanied by a thorough theoretical study with a semi‐empirical model based on coupled wave equations, which is used to investigate the lasing characteristics beyond the manufacturing range. The results can be applied to a broad range of thin‐film DFB resonators, enabling the design of more complex laser stack configurations including light‐emitting devices for current‐injection lasing.

Continuous-Wave Lasing in Perovskite LEDs with an Integrated Distributed Feedback Resonator.

Realization of electrically pumped laser diodes based on solution-processed semiconductors is a long-standing challenge. Metal halide perovskites have shown great potential toward this goal due to theirexcellent optoelectronic properties. Continuous-wave (CW) optically pumped lasing in a real electroluminescent device represents a key step to current-injection laser diodes, but it has not yet been realized. This is mainly due to the challenge of incorporating a resonant cavity into an efficient light-emitting diode (LED) able to sustain intensive carrier injection. Here, CW lasing is reported in an efficient perovskite LED with an integrated distributed feedback resonator, which shows a low lasing threshold of 220Wcm-2 at 110K. Importantly, the LED works well at a current density of 330Acm-2 , indicating the carrier injection rate already exceeds the threshold of optically pumping. The results suggest that electrically pumped perovskite laser diodes can be achieved once the Joule heating issue is overcome.

Lasing by Template‐Assisted Self‐Assembled Quantum Dots

AbstractMiniaturized laser sources with low threshold power are required for integrated photonic devices. Photostable core/shell nanocrystals are well suited as gain material and their laser properties can be exploited by direct patterning as distributed feedback (DFB) lasers. Here, the 2nd‐order DFB resonators tuned to the photoluminescence wavelength of the QDs are used. Soft lithography based on template‐assisted colloidal self‐assembly enables pattern resolution in the subwavelength range. Combined with the directional Langmuir–Blodgett arrangement, control of the waveguide layer thickness is further achieved. It is shown that a lasing threshold of 5.5 mJ cm−2 is reached by a direct printing method, which can be further reduced by a factor of ten (0.6 mJ cm−2) at an optimal waveguide thickness. Moreover, it is discussed how one can adjust the DFB geometries to any working wavelength. This colloidal approach offers prospects for applications in bioimaging, biomedical sensing, anti‐counterfeiting, or displays.

Control of emission diffraction angles and laser threshold in mixed-order sampled distributed feedback laser with organic gain media

The control of laser emission angles in laser devices is essential for many optoelectronic and photonic applications such as optical sensing and displays. In this context, we studied the light diffraction pattern of laser beams in a one-dimensional sampled distributed feedback resonator having organic gain media. The gratings consist of the repetition of supercells having a mixed-order sampled grating in which 1st-order gratings surround a 2nd-order grating. The experimental results showed that the diffraction angles of the laser beams are quite diverse depending on the supercell structures. We demonstrate that the interval of the diffraction angle (θ) of the laser beams is inversely proportional to the length of the supercell experimentally and theoretically. By tuning the length of supercells as well as the length of 1st-order and 2nd-order regions, the interval θ was tuned from 0.1° to 43° with the different arc emission patterns. With the reduction of θ, i.e., the longer 1st-order region, a significant decrease in the laser threshold was obtained, resulting in the lowest lasing threshold of 2.5 ± 0.1 μJ/cm2 with ∼3.5 ns of a long pulse width excitation source.

Reconfigurable Low Phase Noise RF Carrier Generation up to W-Band in Silicon Photonics Technology

Reconfigurable radiofrequency (RF) signal generation in the 30–300 GHz range is attractive for many applications. W-band (75–110 GHz) is currently targeted by both wireless and satellite communications and similar frequency ranges are employed for on-board automotive radar systems. Distribution of high-precision and high-frequency synchronization signals in modern centralized radio access networks might be addressed by radio-over-fiber solutions, but the stringent phase noise (PN) requirements in case of broadband signals with high subcarriers density are not easily attainable through conventional electric-domain solutions. This article reports on the performance of a monolithically integrated silicon photonics (SiP) circuit employed for RF carrier synthesis. Up to sixfold frequency multiplication of an 18.5 GHz reference clock is demonstrated with low additional phase noise. The circuit includes a high-speed electro-optic phase modulator employed for optical frequency comb (OFC) generation and a tunable distributed feedback resonator (DFBR) filter for selecting the desired OFC harmonic. The beating of the OFC tone with the input laser mode in an off-chip photodiode generates the target RF carrier wave. By tuning the reference clock and the DFBR filter, reconfigurable frequency generation up to W-band and beyond is achieved. PN and time jitter (TJ) of the generated RF carriers are experimentally measured, demonstrating a similar performance as of an ideal frequency multiplier. The effect of the noise of DC sources employed for filter tuning is assessed and a counteracting solution is implemented. TJ robustness versus laser drifting is analyzed and the potential for up to elevenfold frequency multiplication (203.5 GHz) is shown.

Silicon-on-Insulator Microwave Photonic Filter With Widely Tunable and Reconfigurable Flat-Top Bandpass Functionality

We report of a silicon photonics (SiP) flat-top bandpass microwave photonic (MWP) filter with large out-of-band power rejection (OBPR) of up to more than 40 dB and exhibiting central frequency tunability over a range as large as 70 GHz, while still guaranteeing a minimum full-span OBPR larger than 25 dB. Furthermore, the RF bandpass transfer function can be widely configured without sacrificing the filter performance. In the present realization, a continuous bandwidth tuning from 5 to 10 GHz (corresponding to a 100% of bandwidth variation) is demonstrated. The operation is based on optical-to-RF mapping the response of a tunable and bandwidth reconfigurable photonic integrated optical filter, realized with a high-order distributed feedback resonator (DFBR) waveguide Bragg grating structure. A high level of functional integration is provided in a compact footprint of less than 2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> by embedding within the circuit a SiP phase modulator generating the modulation sideband scanning the DFBR filter, and a tunable optical splitter optimizing the MWP filter performance. Possibility of further extending system integration for monolithic on-chip operation is also investigated.

Towards facile fabrication of photonics components from inorganic and hybrid sol-gel films. Preparation and optical properties characterization

New trends towards development of integrated optics and miniaturization of photonic devices require fabrication of miniaturized photonic components. Fabrication of waveguiding films with designed optical properties is a fundamental process for production of planar integrated devices.We report here preparation of thin layers based on TiO2 precursor (TET – titanium(IV) ethoxide) and SiO2 precursors, namely inorganic (TEOS – tetraethyl orthosilicate) or organically modified (GLYMO − 3-glycidoxypropyltrimethoxysilane) as candidates for potential application in the planar integrated circuits.The thin layers were deposited on soda-lime glass substrates using the sol-gel method and dip-coating technique and processed at relatively low temperature (up to 300 °C). Several parameters e.g. a) the type of SiO2 precursor, b) the presence of complexing agent for TET and c) heat treatment temperature were tested for their influence on thickness and refractive index of the obtained films.Furthermore, a few series of sol-gel films activated with luminescent dye (Rhodamine B) was fabricated. The influence of the above-listed parameters on luminescent properties of the films was characterized because of lack of systematic study in the literature in this aspect. Moreover, a spectrum of the light at the output of a chosen luminescent dye-doped waveguiding film excited by laser source was investigated.In addition, the subject of our investigations were films prepared at 200 °C with various amounts of TET and organically modified SiO2 precursor in concentration range not presented before. Their optical properties such as homogeneity and values of optical band gap of TiO2 clusters were explored. For selected samples the waveguide properties including the optical losses were evaluated. For the first time, hybrid films with presented composition and refractive index in range of 1.59–1.71 were used for patterning by nanoimprint technique allowing for reproduction of periodic structures, which may serve for example as grating couplers or DFB (distributed feedback) resonators.

Lasing Spaser in Photonic Crystals.

Plasmonic nanolasers (spasers) are of intense interest, attributable to their ability to generate a high-intensity coherent radiation. We infiltrated a three-dimensional silica-based photonic crystal (PhC) film with spasers, composed of spherical gold cores, surrounded by silica shells with dye molecules. In spasers, the gold nanospheres supported the surface plasmons and the dye molecules transferred incoming optical energy to the surface plasmons. Our experiments show that such a structure, consisting of a PhC, which acts as an external distributed feedback resonator, and spasers, can serve as a coherent source of electromagnetic radiation. Spasers were locked in phase by the common radiation causing a phenomenon called the lasing spaser: the emission of spatially and temporarily coherent light normal to the surface of the PhC film. The far-field radiation patterns appeared in the shape of the Star-of-David, which is due to the dispersion along the Brillouin zone boundary. The infiltration of the spasers into the PhC led to drastic narrowing of the emission peak and an 80-fold decrease in the spaser generation threshold with respect to the same spasers in a suspension at room temperature.

Blue and Deep‐Blue‐Emitting Organic Lasers with Top‐Layer Distributed Feedback Resonators

AbstractAll‐solution processed surface‐emitting organic distributed feedback lasers are attractive devices for low‐cost applications. Here, lasers emitting in the spectral region between 375 and 475 nm, in which both active material and resonator (1D relief gratings) are based on solution‐processable polymer films, are reported. Ten different organic compounds dispersed in polystyrene are used as active layers of the prepared devices. They include various carbon‐bridged oligo(p‐phenylenevinylene) (COPVn, with n = 1,2) derivatives and two terfluorene compounds. The synthesis and complete optical and amplified spontaneous emission properties of one of the COPV1 compounds, COPV1(Me)‐t‐Bu, designed for deep‐blue emission, are also included. The feasibility of the resonator fabrication, performed by holographic lithography with a dichromated gelatine photoresist over the active film, is successfully demonstrated for all devices. Remarkably, no resolution limitations are found even for the lowest grating period (235 nm) required for the fabrication of the laser based on COPV1(Me)‐t‐Bu. It is also demonstrated that the rectangular grating profile with duty cycle 0.75:0.25 (hill:valley) is very convenient to optimize the resonator efficacy.

The Leap from Organic Light-Emitting Diodes to Organic Semiconductor Laser Diodes

In recent years, organic light-emitting device technology has expanded from organic light-emitting diodes (OLEDs) to organic semiconductor laser diodes (OSLDs) with the progress of sophisticated mo...

Optically pumped colloidal-quantum-dot lasing in LED-like devices with an integrated optical cavity

Realization of electrically pumped lasing with solution processable materials will have a revolutionary impact on many disciplines including photonics, chemical sensing, and medical diagnostics. Due to readily tunable, size-controlled emission wavelengths, colloidal semiconductor quantum dots (QDs) are attractive materials for attaining this goal. Here we use specially engineered QDs to demonstrate devices that operate as both a light emitting diode (LED) and an optically pumped laser. These structures feature a distributed feedback resonator integrated into a bottom LED electrode. By carefully engineering a refractive-index profile across the device, we are able to obtain good confinement of a waveguided mode within the QD medium, which allows for demonstrating low-threshold lasing even with an ultrathin (about three QD monolayers) active layer. These devices also exhibit strong electroluminescence (EL) under electrical pumping. The conducted studies suggest that the demonstrated dual-function (lasing/EL) structures represent a promising device platform for realizing colloidal QD laser diodes.

Silicon Photonics High-Order Distributed Feedback Resonators Filters

High-order distributed feedback resonators realized in silicon-on-insulator technology for the implementation of high-performance integrated optical filters are reported. This approach combines design simplicity and flexibility in a compact footprint with filter transfer functions featuring a flat-top response, large out-of-band rejection of more than 40 dB, ultra-steep roll-off up to 1000 dB/nm, and unprecedented stopband-to-passband ratios up to 600 for high-index-contrast technology. Active control of the coupled cavities through local micro heaters is employed for optimizing the filter response and passband tuning. Exemplary implementations of a box-like transfer function filter with a bandwidth of 25 GHz and of a narrow linewidth 2 GHz filter realized with 6 th - and 3 rd -order filter designs, respectively, are presented.

Solution-processed nanographene distributed feedback lasers

The chemical synthesis of nanographene molecules constitutes the bottom-up approach toward graphene, simultaneously providing rational chemical design, structure-property control and exploitation of their semiconducting and luminescence properties. Here, we report nanographene-based lasers from three zigzag-edged polycyclic aromatics. The devices consist of a passive polymer film hosting the nanographenes and a top-layer polymeric distributed feedback resonator. Both the active material and the laser resonator are processed from solution, key for the purpose of obtaining low-cost devices with mechanical flexibility. The prepared lasers show narrow linewidth ( < 0.13 nm) emission at different spectral regions covering a large segment of the visible spectrum, and up to the vicinity of the near-infrared. They show outstandingly long operational lifetimes (above 105 pump pulses) and very low thresholds. These results represent a significant step forward in the field of graphene and broaden its versatility in low-cost devices implying light emission, such as lasers.

Accumulation of Distributed Phase Shift in Distributed-Feedback Resonators

Distributed-feedback waveguide lasers based on Bragg-grating resonators generate ultranarrow-linewidth emission. Oscillation at the center of the reflection band ensures maximum reflectivity, hence minimum linewidth. The required π/2 phase shift is often introduced by a distributed change in effective refractive index, e.g., by widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates from the designed wavelength. Even when thermally induced chirp or fabrication errors are negligible, this deviation is still present. Here, we show theoretically and experimentally that this deviation is of fundamental nature. The decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to reflection by the periodic grating and the refractive index change causes an incomplete accumulation of designed phase shift, thereby systematically shifting the resonance to a shorter wavelength. Considering the overlap integral between the distributed phase shift and light intensity in the design provides the desired performance.

Femtosecond tuning dynamics of organic amplifiers based on injection into DFB resonators of slant gratings

We report regenerative amplification of femtosecond laser pulses locked by injection of supercontinuum spectrum into a distributed feedback (DFB) microcavity constructed by slant gratings. Destroying the symmetry of the DFB resonance modes about the normal injection, the slant grating not only enabled concentration of the energy amplification on single modes, but also facilitate continuously tuning of the amplification in a broad band. The injection has locked efficiently the amplification spectrum, the transverse mode and the direction of the output beam, as well as the pulse length. In-plane amplification using a thin-film DFB device and injection locking supplies an important approach to produce high-quality ultrashort-pulsed laser beam from organic semiconductors. Advantages of injection-locked amplification techniques are also largely extended.

Optically pumped rare-earth-doped Al2O3 distributed-feedback lasers on silicon [Invited

This paper reviews recent progress in the field of optically pumped rare-earth-doped channel waveguide lasers, with a focus on operation utilizing distributed-feedback resonators on silicon wafers. Rare-earth-doped amorphous aluminum oxide thin films have been deposited onto silicon wafers by RF reactive co-sputtering from metallic Al and rare-earth targets, the spectroscopy and optical gain of Er3+, Yb3+, Nd3+, and Tm3+ ions has been investigated, and the near-infrared laser transitions near 1 μm in Yb3+, 1.5 μm in Er3+, and 2 μm in Tm3+ and Ho3+ have been demonstrated. Output power between a few μW and hundreds of mW have been achieved in different waveguide geometries, and ultranarrow-linewidth laser operation has been demonstrated.

Temperature dependence of the spectral characteristics of distributed-feedback resonators.

We characterize the spectral response of a distributed-feedback resonator when subject to a thermal chirp. An Al2O3 rib waveguide with a corrugated surface Bragg grating inscribed into its SiO2 top cladding is experimentally investigated. We induce a near-to-linear temperature gradient along the resonator, leading to a similar variation of the grating period, and characterize its spectral response in terms of wavelength and linewidth of the resonance peak. Simulations are carried out, showing good agreement with the experimental results and indicating that the wavelength of the resonance peak is a result only of the total accumulated phase shift. For any chirp profile we are able to calculate the reflectivities at the resonance wavelength, and this information largely explains how the linewidth of the resonance changes. This result shows that the increase in linewidth is governed by the increase of the resonator outcoupling losses.

An Efficient All‐Plastic Organic Waveguide Solid‐State Laser Devices with Distributed Bragg Reflector

Organic dye or polymer waveguide laser is a promising next‐generation solid‐state laser device, because they are not only easily and inexpensively fabricated as laser sources, but also have high potential for bio‐sensing for hazardous materials and environments. The active layer and the effective resonator consist of all‐organic materials, which can be processed by solution‐casting or spin‐coating. Here, laser performances of all‐plastic organic waveguide solid‐state laser devices are reported with Bragg mirror and micro‐cavity, both being fabricated by the relief gratings. Waveguide consists of a high quantum yield organic dye of pyrromethene 567 as a lasing emitter and a cellulose acetate (CA) film as a waveguide matrix. The distributed Bragg reflector (DBR) region and the distributed feedback (DFB) resonator as a micro‐cavity are fabricated in the waveguide devices using a negative photoresist SU‐8 by an interference technique. The performances of lasing threshold and slope efficiency for both organic waveguide devices with DBR region and DFB resonator are evaluated. The slope efficiency of 2.01% and the lasing threshold of 45 µJ cm−2 are measured for the waveguide device with DBR region, whereas the waveguide device with DFB resonator gives the slope efficiency of 0.72% and the lasing threshold of 140 µJ cm−2.

Single transverse mode protein laser

Here, we report a single transverse mode distributed feedback (DFB) protein laser. The gain medium that is composed of enhanced green fluorescent protein in a silk fibroin matrix yields a waveguiding gain layer on a DFB resonator. The thin TiO2 layer on the quartz grating improves optical feedback due to the increased effective refractive index. The protein laser shows a single transverse mode lasing at the wavelength of 520 nm with the threshold level of 92.1 μJ/mm2.

All-inorganic perovskite-based distributed feedback resonator.

Halide perovskite materials have rapidly emerged as outstanding optoelectronic materials for solar cells, light-emitting diodes (LEDs), and lasers. Compared to hybrid organic-inorganic perovskites, all-inorganic perovskites have shown unique merits that may contribute to the ultimate goal of developing electrically-pumped lasers. In this paper, we demonstrate a distributed feedback (DFB) resonator using an all-inorganic perovskite thin film as the gain medium. The film has a gain coefficient of 161.1 cm-1 and a loss coefficient of 30.9 cm-1. Excited by picosecond pulses, the microstructured all-inorganic perovskite film exhibits a single-mode emission at 654 nm with a threshold of 33 μJ/cm2. The facile fabrication process provides a promising route towards low-cost single-mode visible lasers for many practical applications.