Tunable Distributed Bragg Reflector Research Articles

Tunable distributed Bragg reflector developed by magnetron sputtering to improve the power conversion efficiency of transparent IR cells for solar energy harvesting applications

Transparent organic photovoltaic (TOPV) cells integrated into windows are key to reducing the carbon dioxide emissions associated with the building sector. However, TOPV cells that reach a compromise between efficiency and transparency must still be developed. In addition, to implement this technology in glass production companies, the materials and processes used in TOPV cell development must be compatible with producing these devices on an industrial scale. Here, an infrared (IR) cell combining a PC60BM-based active material, ITO/ZnO as the back transparent electrode, PEDOT:PSS and ITO or Ag as the top transparent electrode, and a DBR as an antireflective coating was developed and applied on 625 mm2 glass samples. The structure of the DBR based on titanium dioxide (TiO2) and silicon dioxide (SiO2) monolayers was adjusted to the IR cell absorption spectra to reach a power conversion efficiency (PCE) of 5 and 4.3, and an average visible transmission (AVT) of 41 % and 51 % for ITO and Ag top electrodes, respectively. The manufacturing route of these devices involved commercial polymers and coatings that can be deposited by technologies already applied in the glass industry, such as magnetron sputtering or thermal evaporation. Therefore, the IR cells developed here showed a good compromise between efficiency, transparency, and large-scale production manufacturability.

Fiber Bragg gratings fabricated in fibers with different geometries by femtosecond laser written through the coating and their applications in strain sensing and fiber laser

Applications of the type-I fiber Bragg gratings (FBGs) written through the coating (TTC) in strain sensing and tunable distributed Bragg reflector (DBR) fiber lasers were demonstrated. We reported the principle of selecting the distance between the fiber and the phase mask when writing type-I TTC FBGs. Type-I TTC FBGs written in commercially available acrylate-coated fibers with various geometries and their strain responses were demonstrated. Results showed that the strain sensitivity of FBGs increases as the core-diameter decreases, probably due to the waveguide effect. In addition, a continuously tunable DBR fiber laser based on TTC FBGs was achieved with a wavelength tuning range of 19.934 nm around 1080 nm, by applying a strain of 0-21265.8 µɛ to the laser resonant cavity. The wavelength tuning range was limited by the splice point between the gain fiber and the passive fiber for transmitting pump and signal lasers. When the pump power was 100 mW, the relative intensity noises were −97.334 dB/Hz at the relaxation oscillation peak of 880 kHz and −128 dB/Hz at frequencies greater than 3 MHz. The results open a potential scheme to design and implement continuously tunable fiber lasers and fiber laser sensors for strain sensing with a higher resolution.

Monolithically Integrated Tunable Three- Section All-Active DBR Laser Diodes With 30 nm Tuning Range

We present a monolithically integrated three-section all-active AlGaInAs/InP tunable distributed Bragg reflector (DBR) ridge waveguide laser diode that uses thermal tuning mechanism and mode-hopping tuning principle to achieve wide-range wavelength tuning. It is similar to the traditional three-section DBR laser structure, including a gain section, a phase section, and a DBR grating section. The difference is that the phase section and the DBR section incorporate the same active quantum well structure as the gain section. In this case, weak effective refractive index changes of the three active sections affected by the current injection will occur since the carrier density is clamped by the threshold gain condition of the DBR laser diode. Despite this limitation, a noncontinuous tuning up to ∼30 nm (1564–1594 nm) can be observed using only current injection at a constant temperature of 25 °C. Significant thermal effects occurred during the tuning process. In addition, a discontinuity is introduced in the tuning because it does not contain a passive region for phase adjustment. However, the device still provides a stable single longitudinal mode output with nine channels, a wavelength spacing of about 4 nm, and a side mode suppression ratio (SMSR) of more than 30 dB. Furthermore, the DBR laser diode can be easily fabricated utilizing the conventional distributed feedback laser diode fabrication process without secondary epitaxy and heater metal. The all-active DBR laser diode will be expected to be applied in the coarse wavelength division multiplexing (CWDM) systems with the advantage of low cost.

Optofluidic tunable broadband distributed Bragg reflector based on liquid crystal polymer composites.

A dynamically reconfigurable liquid crystal (LC) photonic device is an important research field in modern LC photonics. We present a type of continuously tunable distributed Bragg reflector (DBR) based on LC polymer composites modulated via a novel optofluidic method. LC-templated DBR films are fabricated by photopolymerization under visible standing wave interference. The influences of the incident angle, incident light intensity, and content of ethanol as a pore-forming additive on the reflection behavior are discussed in detail. Then, the LC-templated DBR films are integrated into microfluidic channels and reversibly refilled by different organic solvents. The reconfigurable characteristics of optofluidic DBRs were demonstrated by changing the average refractive index (RI) of the mixed liquids and adjusting the flow rates, resulting in the dynamic and continuous variation of the reflection band within a specific visible light band. It is anticipated that the prototype optofluidic LC device will hopefully be applied to some specific scenarios where conventional means of regulation, such as electric, optical, and temperature fields, are unsuitable and possibly boost the development of microfluidic analysis techniques based on structural color.

Enhanced direct modulation bandwidth in a tunable DBR laser with an equivalent phase shift grating

A high speed directly modulated and tunable distributed Bragg reflector laser is proposed based on an equivalent phase shift Bragg grating. By inserting a uniform waveguide in the middle of Bragg grating section, a notch is formed on reflectivity spectrum of the grating, and the photon-photon resonance (PPR) effect could then be introduced to extend modulation bandwidth. An independent electrode is also added for controlling the equivalent phase shift, which plays a key role in the design to introduce the PPR effects, and ensure compatibility with wavelength tuning. Stability, tunability and small signal response of the laser are numerically investigated, 40 GHz direct modulation bandwidth and 7 nm tuning range are obtained, indicating that the laser designed could achieve a large modulation bandwidth within a certain wavelength tuning range.

Influence of Losses on the Laser Voltage Drop of the Active Section

We present a model of a tunable distributed Bragg reflector (DBR) laser describing the effect of cavity losses on the gain voltage. Theoretical and experimental results are in good agreement. Measurements show the gain voltage trace for Bragg grating and phase section tuning. The model is also valid for lasers with optical feedback from an external reflection.

A 1.6-[formula omitted]m widely tunable distributed Bragg reflector laser diode based on InGaAs/InGaAsP quantum-wells material

We demonstrate a widely tunable InGaAs quantum-wells (QWs) distributed Bragg reflector (DBR) laser, in which the DBR section was realized by using butt-jointed InGaAsP (λ=1.46μm) material. In the device process, we explored an optimal chemical etchant applied in the butt-jointed active–passive integration technology. A wide tuning range of 10.7 nm with 19 consecutive channels is obtained with a single tuning current at room temperature (RT). With the help of the heat sink temperature, the tuning range is expanded to 16 nm. A side mode suppression ratio (SMSR) of higher than 34 dB is obtained for all channels at 5 °C to 45 °C. A six-wavelength laser array that can cover a wavelength tuning range of 41.6 nm at 20 °C with a side mode suppression ratio higher than 37 dB in all channels is demonstrated by varying the grating periods. It is a promising light source for methane or multispecies gas detection.

A Widely Tunable Three-Section DBR Lasers for Multi-Species Gas Detection

We demonstrate a widely tunable distributed Bragg reflector (DBR) laser operating at 1.8-µm, in which the DBR section was butt-jointed InGaAsP (λ = 1.45 μm) material. Through current and temperature tuning, a widely tuning range of over 11 nm with a side mode suppression ratio (SMSR) higher than 30 dB is obtained. Utilizing this DBR laser, the water and methane detection experiment has been successfully implemented, which illustrates the potential capacity of such DBR laser as the light source used for multispecies gas sensing. The work also illustrates that the butt-joint active-passive integration technology developed for the InGaAsP quantum-wells (QWs) can be successfully applied in the InGaAs QWs.

Up to 50 Gb/s modulation of an EAM integrated widely tunable DBR laser

An electro-absorption modulator (EAM) integrated widely tunable distributed Bragg reflector (DBR) laser working at 1.5 µm is reported. By utilizing the RF resonance between the bonding wire and the EAM, a 28 GHz modulation bandwidth is obtained. The device is modulated with up to 50 Gb/s NRZ data. At 28 Gb/s, the power penalty to obtain a 10-10 bit error rate (BER) after a 5 Km standard single mode fiber transmission is less than 0.7 dB. Because the DBR material has a long bandgap wavelength, the wavelength tuning range of the laser is larger than 12 nm. The DBR laser is a promising low cost tunable light source for future high capacity wavelength division multiplexing (WDM) optical communication systems.

A10 Gb/s 1.5 μm Widely Tunable Directly Modulated InGaAsP/InP DBR Laser**Supported by the National Key Research and Development Program of China (Grant Nos. 2017YFF0206103, 2016YFB0402301, and 2018YFB2200801) and the National Natural Science Foundation of China (Grant Nos. 61635010, 61320106013, 61474112, and 61574137).

We report 10 Gb/s data transmissions using a packaged two-section InGaAsP/InP distributed Bragg reflector (DBR) laser. The tunable DBR laser has a wavelength tuning range of 12.12 nm. The DBR laser has greater than 10.84 GHz 3-dB direct modulation bandwidth within the wavelength tuning range. The 10 Gb/s data transmissions are performed at up to a distance of 30-km.

Effect of Optical Feedback on the Wavelength Tuning in DBR Lasers

Optical feedback has an impact on the tunability of lasers. We created a model of a tunable distributed Bragg reflector (DBR) laser describing the effect of optical feedback from a constant reflector distance on the wavelength tuning. Theoretical and experimental results are in good agreement. A further discussion of the model sheds light on design rules to reduce the effect of optical feedback on the tuning behavior. We introduced a new parameter called mode loss difference (MLD) as a metric for the feedback tolerance of the tuning behavior. A large MLD indicates higher tolerance of the laser to cavity length variations.

Continuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser

We analyse the use of a tunable dual wavelength Y-branch DBR laser diode for THz applications. The laser generates electrically tunable THz difference frequencies in the range between 100 and 300 GHz. The optical beats are tuned via current injection into a micro-resistor heater integrated on top of one of the distributed Bragg reflector (DBR) section of the diode. The laser is integrated in a homodyne THz system employing fiber coupled ion-implanted LT-GaAs log spiral antennas. The applicability of the developed system in THz spectroscopy is demonstrated by evaluating the spectral resonances of a THz filter as well as in THz metrology in thickness determination of a polyethylene sample.

1.3-µm and 10-Gbps tunable DBR-LD for low-cost application of WDM-based mobile front haul networks.

We report a 1.3-µm and 10-Gbps tunable distributed Bragg reflector laser diode (DBR-LD) for the low-cost application of a wavelength division multiplex based mobile front-haul network. The device consists of gain, phase control, and DBR sections, implemented using a butt-coupling method through a monolithic integration and through the introduction of an etched mesa planar buried hetero-structure in a waveguide structure. From the work, a 560-µm long DBR-LD with a 220-µm long micro-heater DBR section has a threshold current of 10 mA ± 1 mA and a tuning range of more than 15 nm within a heater injection current of ∼100 mA. Spectral and dynamic tests for this LD show 16 channels spaced a wavelength grid of 0.8 nm with a side mode suppression ratio of greater 40 dB and clear eye openings with a dynamic extinction ratio of over 5.4 dB at an operating current of 60 mA.

High-Resolution Optical Frequency Synthesis Using an Integrated Electro-Optical Phase-Locked Loop

Optical frequency synthesizers have widespread applications in optical communication, sensing, and ranging systems. These synthesizers typically consist of an electro-optical phase-locked loop (EOPLL) that phase locks a widely tunable laser (TL) to the teeth of a highly stable optical frequency comb. In this paper, a partially integrated optical frequency synthesizer is reported, where a stable and low-noise frequency comb is used as the optical reference. In the proposed architecture, frequency synthesis is done in two phases. In a coarse tuning phase, a widely tunable distributed Bragg reflector laser is continuously tuned by adjusting its mirrors and phase section currents. While the laser is being tuned, an indexing system detects and counts the number of passing comb teeth. Coarse tuning is concluded when the TL reaches the target comb tooth. Following the coarse tuning phase, a heterodyne integrated EOPLL phase locks the TL to the selected comb tooth. Under the phase lock condition, fine frequency tuning is performed by adjusting the frequency of an RF local oscillator. The proposed synthesizer has the capability of synthesizing optical frequencies over a 5-THz range with a coarse tuning speed of 0.5 THz/s and coarse and fine tuning resolutions of 20 MHz and less than 1 Hz, respectively.

10 Gb/s Data Transmissions Using a Widely Tunable Directly Modulated InGaAlAs/InGaAsP DBR Laser

We report data transmissions using a packaged two-section distributed Bragg reflector (DBR) laser, which has InGaAlAs multi-quantum wells as the gain material. The tunable DBR laser has a wavelength tuning range of 11.44 nm. The DBR laser has uniform 3-dB direct modulation bandwidth (over 12 GHz) within the over 11-nm wavelength tuning range; 10-Gb/s data transmissions are performed at up to 25-km distance and different wavelength emissions at 25 °C and 50 °C.

Data Transmission Using a Directly Modulated Widely Tunable DBR Laser With an Integrated Ti Thin Film Heater

We present data transmission using a directly modulated distributed Bragg reflector (DBR) laser having an integrated Ti thin film heater in the DBR section and butt-jointed InGaAsP as DBR material. By combining DBR current tuning and thermal tuning effects, an over 16 nm wavelength tuning range is obtained. 5 Gb/s data transmissions are conducted at up to 25 km distance and different wavelengths. In the fabricated device, the butt-jointed InGaAsP material is also used for the formation of an integrated photodiode for monitoring the light power of the device.

Research on the influence of laser-tuning characteristics on all-fiber distributed Bragg reflector self-mixing rangefinder

We proposed an all-fiber tunable distributed Bragg reflector (DBR) laser rangefinder, which realized high-accuracy measurement of the absolute distance in the range of 1.88 to 3.33 m based on the self-mixing effect. The theoretical analysis of the all-fiber tunable DBR laser shows that wavelength tuning range and frequency of the laser can influence the measurement range and resolution. In addition, the experimental results indicate that the influence factors of measurement accuracy and sensitivity in absolute distance measurement are modulation response linearity, experimental equipment, and circuit bandwidth, which is in good agreement with theory analysis. Moreover, increasing the linear wavelength tuning range of the tunable DBR laser is an essential method to improve the measurement accuracy and sensitivity of the absolute distance measurement system.

Transmission of 20 Gb/s PAM-4 signal over 20 km optical fiber using a directly modulated tunable DBR laser

We report 20 Gb/s transmission of four-level pulse amplitude modulation (PAM) signal using a directly modulated tunable distributed Bragg reflector (DBR) laser. Transmission distance over 20 km was achieved without using optical amplifiers and optical dispersion compensation modules. A wavelength tuning range of 11.5 nm and a 3 dB bandwidth greater than 10 GHz over the entire wavelength tuning range were obtained.

Widely Tunable Two-Section Directly Modulated DBR Lasers for TWDM-PON System**Supported by the National Key Project under Grant No 2016YFB0402301, the National High Technology Research and Development Program of China under Grant No 2013AA014502, and the National Natural Science Foundation of China under Grant Nos 61635010, 61320106013, 61474112, 61321063 and 61274071.

Wavelength tunable and directly modulated distributed Bragg reflector (DBR) lasers with butt-joint technology are designed, fabricated and characterized. The DBR laser consists of a gain section and a DBR section. To increase the electrical isolation between the gain section and the DBR section, parts of a p-doped material in the isolation region are etched off selectively. Over 2 kΩ isolation resistance is realized ultimately without the need of ion implantation, which simplifies the fabrication process. The laser exhibits high speed modulation with a large tunable range. The 3 dB direct modulation bandwidth of the device is over 8 GHz in a 12 nm tunable range. This widely tunable DBR laser with the simple structure is promising as a colorless light source for the next-generation time and wavelength division multiplexed passive optical network (TWDM-PON) systems.

High-speed directly modulated widely tunable two-section InGaAlAs DBR lasers.

We report widely tunable two-section distributed Bragg reflector (DBR) lasers, which have InGaAlAs multiple quantum wells (MQWs) as the gain material. By butt-jointing InGaAsP, which has a photoluminescence wavelength of 1.4 μm as the material of the DBR section, a wavelength tuning range of 12 nm can be obtained by current injection into the DBR section. The direct modulation bandwidth of the lasers is greater than 10 GHz over the entire wavelength tuning range up to 40°C. Compared with InGaAsP DBR lasers having the same structure, the InGaAlAs lasers have smaller variations in both the threshold current and slope efficiency with the temperature because of the better electron confinement in the InGaAlAs MQWs. Moreover, the DBR-current-induced decreases in the modulation bandwidth and side mode suppression ratio (SMSR) of the optical spectra are notably smaller for the InGaAlAs lasers than for the InGaAsP lasers.