Grating Bragg Reflector Research Articles

Monolithically integrated multimode interference coupler-based master oscillator power amplifier with dual-wavelength emission around 830 nm

A monolithically integrated dual-wavelength multimode interference coupler-based master oscillator power amplifier is presented. It consists of two shallowly etched, laterally separated ridge waveguide laser cavities as master oscillators with individual distributed Bragg reflector gratings as cavity mirrors. A deeply etched coupling section containing S-bend shaped waveguides and a multimode interference coupler is used to couple the laser emission of the master oscillators into a shallowly etched single waveguide serving as power amplifier. Changing the etch depth for the coupling section enables a compact device layout. In addition, increased radiation angles of modes not coupled into the power amplifier help to suppress beam steering, otherwise indicated by laterally separated far-field intensity distributions. The device provides 0.5 W of dual-wavelength emission around 830 nm in individual and common operation. As designed, both emission wavelengths are separated by 0.5 nm with spectral widths below 20 pm, limited by the spectral resolution of the spectrometer. Both peak wavelengths remain within spectral windows of 50 pm within the available power range. This enables full flexibility selecting operating points for applications such as shifted excitation Raman difference spectroscopy and the generation of THz emission by photomixing. The emission wavelengths can additionally be non-continuously tuned by applying a heater current to resistors implemented next to the distributed Bragg reflector gratings. As an example, selected spectral distances of 0.5 nm, 1.0 nm, 1.5 nm, and 2.0 nm are demonstrated. Near field widths of 5 μm and far field angles of 17° result in beam propagation ratios of 1.4 (1/e2) in all operation modes and enable easy beam shaping or optical single-mode fiber coupling.

A 0.45 pm of linewidth, single-longitudinal-mode Tm:YLF laser based on reflecting Bragg gratings and Fabry-Perot etalons

Based on the reflecting Bragg gratings (RBG) combined with the Fabry-Perot (F–P) etalon mode selection technique, a diode-pumped single-longitudinal-mode (SLM) Tm:YLF laser output has been obtained. The optimal insertion angle of double F–P etalons is simulated and analyzed theoretically. Fine-tuning the insertion angle of the F–P etalon to match the central wavelength of the RBG. The out wavelength of the Tm:YLF laser is locked in 1907.8 nm. Finally, under the condition of a resonator length of 55 mm and a pump power of 10.15W, an SLM laser output with an output power of 250 mW and an output linewidth of 37.5 MHz (about 0.45pm) is obtained. The power instability is less than 2% within 300s.

High-Performance Grating Coupler Array on Silicon for a Perfectly-Vertically Mounted Multicore Fiber

High performance grating coupler array for coupling of a silicon photonic chip to a multi-core fiber mounted perfectly vertical to the chip surface is proposed and demonstrated. Experimental results show a low coupling loss of −0.8 dB with 1-dB bandwidth of 47 nm, a low back reflection of <−15.8 dB in about 40 nm wavelength range, a channel non-uniformity of 0.9 dB, and crosstalk of <−40 dB. These improved results attribute to the design of embedding the diffractive grating in a one-port cavity formed by partially and perfectly reflecting Bragg gratings on the silicon chip and a metal mirror on the chip surface.

Dual-wavelength operation of a tapered laser diode based on a composite DBR grating near 1.03 µm.

A novel monolithic dual-wavelength tapered laser diode based on a composite distributed Bragg reflection (DBR) grating is demonstrated. The composite DBR grating, composed of two sub-gratings with different effective refractive indices, is designed. With the aid of the lateral expansion effect of the optical field in the ridge waveguide, the dual-wavelength operation of tapered laser diode is realized by using the composite DBR grating as a narrow linewidth filter. At the ridge current of 190-300 mA and the heat sink temperature of 20℃, the tapered laser diode obtains dual-wavelength emission with wavelengths of 1025.4 nm and 1036.2 nm, respectively. The linewidths of both wavelengths are less than 36 pm, and the minimum power difference between the two wavelengths is 1.2 dB. The spectral distance between the two wavelengths can be modulated from 10.4 nm to 10.9 nm by adjusting the heat sink temperature of the tapered laser diode from 13.8℃ to 20.7℃.

A high-Q mid-infrared Tamm plasmon absorber using MgF2 and Ge aperiodic tandem films designed by the genetic algorithm

A high-Q mid-infrared Tamm plasmon (TP) absorber using MgF2 and Ge aperiodic tandem films is designed by the genetic algorithm and fabricated by electron beam evaporation and magnetron sputtering. Such a design circumvents the need for the distributed Bragg reflector grating, and the thickness of individual MgF2 films is much smaller than a quarter of wavelength in films (λ/4n). The fabricated TP absorber exhibits a high and sharp absorption peak at 2.73 μm with a quality factor (Q) of 144, while the simulated counterpart has the absorption peak at 2.72 μm with a Q of 155. The profiles of an electromagnetic field in the tandem films are also simulated to reveal the mechanism of narrow thermal emission. Such a high-Q TP absorber is very promising in the mid-infrared simulator and detection.

Spatial and spectral filtering of tapered lasers by using tapered distributed Bragg reflector grating

A 1040 nm tapered laser with tapered distributed Bragg reflector (DBR) grating is designed and fabricated. By designing the grating with tapered layout, the tapered DBR grating exhibits the scattering effect on side backward-traveling waves, thus achieving additional suppression of parasitic oscillation. Under the suppression of parasitic oscillation, the spatial and spectral characteristics of the tapered laser are improved. The experimental results show that a near-Gaussian far-field distribution and a kink-free P–I characteristics are achieved, and a single peak emission with a wavelength of 1046.84 nm and a linewidth of 56 pm is obtained.

Ten emitter dual-wavelength Y-branch DBR laser diode array emitting 1 W at 785 nm with a spectral emission width below 60 pm

We present a 5 mm wide ten emitter dual-wavelength Y-branch DBR laser diode array emitting at 785 nm with an output power of 1 W at both wavelengths. The two emission wavelengths are individually addressable. The emitters are spectrally stabilized by deeply etched 10th order Distributed Bragg Reflector (DBR) gratings, realized by e-beam lithography. The wavelengths at 1 W output power are 784.0 nm and 784.6 nm. The spectral width of the emission of the individual emitters is below 20 pm. The spectral width of the array at 1 W is less than 60 pm caused by a variation in emission wavelength of about 40 pm of the individual emitters operating at one wavelength. The ten individual emitters reach an optical output power of 100 mW with minor variation of only 5 mW.

High Power 980-nm Broad-Area Lasers with Distributed Bragg Reflection Grating

High-power and highly stable 980 nm semiconductor lasers are widely used in fiber laser pumping and instrumentation applications. We report on a distributed Bragg reflector (DBR) semiconductor laser manufactured on the waveguide structure of an asymmetric large optical cavity. Wavelength stabilization is achieved using a 500-µm-long DBR with a sixth-order Bragg grating, which is fabricated using a combination of electron beam lithography and inductively coupled plasma etching. When the device injection current is 22 A, the output power ranges up to 16 W, the slope efficiency is 0.73 W/A, and a spectral linewidth of 1.4 nm is achieved.

High-Power (&gt;300 mW) On-Chip Laser With Passively Aligned Silicon-Nitride Waveguide DBR Cavity

We demonstrate a high-power on-chip 1550-nm laser implemented by passive flip-chip integration of a curved-channel, double-pass InGaAsP/InP slab-coupled optical waveguide amplifier (SCOWA) onto a photonic integrated circuit (PIC) containing a silicon nitride (SiN) waveguide and distributed Bragg reflector (DBR) grating. The combined chip-scale SCOW external cavity laser (SCOWECL) has single mode emission with 312 mW of optical power at a drive current of 2.5 A, and exhibits a side mode suppression ratio (SMSR) of 55 dB, peak photon conversion efficiency (PCE) of 10%, low relative-intensity noise (RIN) of ~160 dB/Hz, and an integrated linewidth of 192 kHz. Additionally, we demonstrate a multi-wavelength SCOWECL array comprised of four SCOWAs coupled to SiN-waveguide DBR gratings. The four-element array generates 80 mW per channel when the SCOWAs are driven in parallel (1.25 A/channel) with ~1-nm wavelength spacing centered at 1533 nm. We describe the fabrication and hybrid integration processes. The measured SCOWA-to-waveguide coupling loss is estimated to be 1.6 +/-1.0 dB which agrees well with the simulation.

Holographic reflective Bragg gratings of gain and their role in the operation of high-power pulsed lasers

The influence of reflective Bragg gratings that are formed in an active medium due to the spatial periodic modulation of gain on the spectral properties of lasing are investigated by an example of a pulsed Nd : YAG laser. It is shown that, at a certain choice of the formation regime of reflective gratings of gain, the lasing bandwidth can be reduced by a factor of 3 – 5, with a corresponding increase in the pulse energy and significant improvement of spatial beam quality.

Dual-wavelength DBR laser integrated with high-speed EAM for THz communications.

We report a novel single-cavity dual-wavelength laser that has two distributed Bragg reflector (DBR) gratings at each side of a gain section for THz communication applications. By varying the inject current of one of the DBR gratings, the optical beat frequency of the laser can be widely tuned. In the device, a high-speed electro-absorption modulator (EAM) is also integrated and can be used for up to 25 Gb/s data modulation.

III–V/Si Hybrid Laser Array with DBR on Si Waveguide**Supported by the National Basic Research Program of China under Grant No 2013CB632105, the National High Technology Research and Development Program of China under Grant No 2012AA012203, and the National Natural Science Foundation of China under Grant Nos 61404003 and 11174018.

We report an eight-channel silicon evanescent laser array operating at continuous wave under room temperature conditions using the selective-area metal bonding technique. The laser array is realized by evanescently coupling the optical gain of InGaAsP multi-quantum wells to the silicon waveguides of varying widths and patterned with distributed Bragg reflector gratings. The lasers have emission peak wavelengths in a range of 1537–1543 nm with a wavelength spacing of about 1.0 nm. The thermal impedances ZT of these hybrid lasers are evidently lower than those DFB counterparts

Proposal for Slepian-States-Based DV- and CV-QKD Schemes Suitable for Implementation in Integrated Photonics Platforms

Quantum key distribution (QKD) leverages underlying principles of quantum mechanics to realize distribution of keys with verifiable security. Despite appealing features of QKD, there are some fundamental and technical challenges that need to be solved prior to its widespread applications. First, QKD secret-key rate (SKR) is fundamentally limited by channel loss, as dictated by the rate-loss tradeoff. Quantum repeaters would be an ultimate solution to overcome this problem; however, they are well beyond the reach. The second challenge lies in the scalability and cost. Future's QKD systems must be suitable for mass production with low cost, reliable realignment-free operations, and small power consumption. To solve for these problems in a simultaneous manner, we propose to encode information in the orthogonal Slepian sequences’ bases. Such an approach is highly robust against turbulence effects in free-space optical links and dispersion effects/fiber nonlinearities in fiber-optics channels, thereby improving QKD distance. Moreover, exploiting multidimensional encoding space enables high spectral efficiency QKD so that the SKR can be significantly improved. Critically, generation, processing, and detection of Slepian states can be reliably implemented in an integrated quantum photonics platform, based on both reflective and transmissive waveguide Bragg gratings (WBGs). Proposed reflective/transmissive WBG-based Slepian states are applicable to both discrete variable and continuous variable QKD systems.

Design of an augmented reality display based on polarization grating**Project supported by the National Natural Science Foundation of China (Grant No. 11574211).

A new optical system for an augmented reality (AR) display is proposed in this paper. The optical system mainly includes a ray deflector, coupling input grating, optical waveguide, and coupling output grating. Both the ray deflector and the coupling input grating are designed based on the diffraction characteristics of the polarization grating, and the coupling output grating is the Bragg reflection grating. Compared with other AR schemes, this AR optical system not only reduces the number of projections from two to one, but also improves the efficiency of light coupling into the optical waveguides. The energy loss is reduced by utilizing the single-order diffraction characteristics of the polarization grating in its coupling input structure. The light deflector uses the polarization selectivity of the polarization grating and the characteristics of the rotating light of the twisted nematic liquid crystal layer to realize beam deflection. The working principle of the optical system is experimentally and theoretically demonstrated.

Fabrication of high-precision reflective volume Bragg gratings.

Reflecting Bragg gratings (RBGs) recorded in photo-thermo-refractive (PTR) glasses have been widely used in narrowing and stabilization of the laser emission spectrum. As the center wavelength of RBGs determines the final output wavelength of lasers, it is necessary to carefully control the center wavelength of RBGs during the fabrication process. In this paper, the fabrication process of high-precision RBGs was investigated. We developed a two-step method and demonstrated both theoretically and experimentally that it is effective and can be used to guide the fabrication process of high-precision RBGs. The experimental results show that the center wavelength of the fabricated RBG deviates from the target center wavelength within ±10 pm.

Lab-on-Fiber Nanoprobe with Dual High-Q Rayleigh Anomaly-Surface Plasmon Polariton Resonances for Multiparameter Sensing

Surface plasmon resonance (SPR) based sensing is an attractive approach for realizing lab-on-fiber nanoprobes. However, simultaneous measurement of multiple parameters (e.g., refractive index and temperature) with SPR-based nanoprobes, although highly desirable, is challenging. We report a lab-on-fiber nanoprobe with dual high-Q Rayleigh anomaly (RA)-surface plasmon polariton (SPP) resonances for multiparameter sensing. To achieve high-Q RA-SPP resonance the nanoprobe employs a plasmonic crystal cavity enhanced by distributed Bragg reflector (DBR) gratings on the end-face of a single-mode optical fiber. By tailoring the grating periods of the plasmonic crystal cavity and DBRs, two spatially separated high-Q RA-SPP resonance modes are designed within a 50 nm spectral range in C + L band. The fabricated nanoprobe demonstrates two RA-SPP resonances near 1550 nm with high Q-factors up to 198. These two high-Q resonances are further showed to exhibit distinctive responses to the changes of refractive index and temperature, which enables simultaneous measurements of both parameters. The proposed lab-on-fiber nanoprobes will pave the way for realizing compact multiparameter sensing solutions compatible with optical communication infrastructures.

基于反射式布拉格光栅和Fabry-Perot标准具组合的Nd∶YVO4单频激光器

基于反射式布拉格光栅和Fabry-Perot标准具组合的Nd∶YVO₄单频激光器

Direct inscription and evaluation of fiber Bragg gratings in carbon-coated optical sensor glass fibers for harsh environment oil and gas applications.

In this research work, we show the successful inscription of fiber Bragg gratings into carbon-coated pure silica as well as germanium-doped glass fibers by applying the pulsed laser point-by-point manufacturing technique. First, the parameters used for the Ti:sapphire femtosecond laser process are demonstrated. Without removing the polymeric carbon coating, destruction-free formation of highly reflective Bragg gratings is performed with selected types of hermetically enclosed fibers. We demonstrate the advantage of the carbon coating by long-term exposure to a pure hydrogen atmosphere at an elevated temperature. Such harsh conditions exist in the oil and gas industry, which means there is high application potential for technologically advanced optical sensors. Compared to the also examined standard glass fibers with a distinct signal attenuation, carbon-coated fibers show no significant degradation. Finally, we analyze the mechanical stability of the processed fibers via standardized tensile tests. No substantial decrease in strength occurs among the sensor-integrated samples.

Rapid and adjustable shifted excitation Raman difference spectroscopy using a dual‐wavelength diode laser at 785 nm

AbstractIn this paper, we present rapid and adjustable shifted excitation Raman difference spectroscopy (SERDS). A dual‐wavelength diode laser emitting at 785 nm is used as the excitation light source. Two laser resonators are realized in a single chip, and two distributed Bragg reflector gratings provide two excitation lines at 785 nm. For each laser line, an optical power of 170 mW is achieved. Two separate heater elements are implemented and are used to realize a flexible spectral distance up to 36 cm−1. At selected spectral distances from 1 to 30 cm−1, an alternating operation with modulation frequencies up to 100 Hz is performed and shows stable spectral properties including a narrow linewidth of 11 pm. Raman experiments are carried out using ethanol as the target substance and Irish cream as the test sample. Raman and SERDS spectra at the selected spectral distances are presented and discussed with respect to the analytes under study. The described alternating operation for SERDS is demonstrated with integration times down to 50 ms for a single Raman spectrum. A carefully selected spectral distance of 15 cm−1 between both laser lines allows a discrimination of closely neighbored Raman bands of Irish cream and shows a 15‐fold improvement of the signal‐to‐background noise in the reconstructed SERDS spectra. The results demonstrate rapid and adjustable SERDS using a dual‐wavelength diode laser as a potential tool for Raman applications such as real‐time diagnostic during surgeries, in situ measurements, which require quick on‐site decisions, and Raman experiments with strong background interferences, for example, from laser‐induced fluorescence and ambient light.

Characterization of Low Loss Waveguides Using Bragg Gratings

A novel approach is developed for measuring small losses in highly transparent Si3N4/SiO 2 waveguides on a silicon chip. The approach is particularly applicable to waveguides written by high-resolution patterning techniques, such as e-beam lithography, whose lengths cannot be easily increased beyond several centimeters. This method is based on measuring the transmission of an optical cavity formed by two highly reflective ( R at least 0.999) simple Bragg gratings and a uniform waveguide between the two gratings whose length can be varied to increase the loss fitting accuracy. A theoretical model based on an ABCD matrix method is developed and used for the final loss value fitting. Experimentally, a cavity with extinction ratio over –70 dB and quality factor Q = 1.02×106 is realized. The fitting results show a waveguide loss of 0.24 ± 0.01 dB/cm and a grating loss of 0.31 ± 0.01 dB/cm. These results are obtained with relatively high index contrast ( Δn > 0.001) gratings with 0.1-pm wavelength scanning resolution. It is expected that with better design and wavelength scanning technique, this approach is applicable more generally to measure waveguide loss coefficients as low as 0.001 dB/cm.