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A novel high-speed directly modulated two-section distributed-feedback (TS-DFB) semiconductor laser based on the detuned-loading effect is proposed and simulated. A grating structure is designed by the reconstruction-equivalent-chirp (REC) technique. A π phase shift is introduced into the reflection grating, which can provide a narrow-band reflection region with a sharp falling slope on both sides of the reflection spectrum, thus enhancing the detuned-loading effect. Owing to its unique dual-falling-edges structure, the bandwidth can be improved even when the lasing wavelength shifts beyond the left falling edge due to a thermal effect in the actual test, in which condition the detuned-loading effect can be used twice, which greatly improves the yield. The modulation bandwidth is increased from 17.5 GHz for a single DFB laser to around 24 GHz when the lasing wavelength is located on the left falling edge of the TS-DFB laser based on the detuned-loading effect, and it can be increased to 22 GHz for the right side. An eight-channel laser array with precise wavelength spacing is investigated, with a side-mode suppression ratio (SMSR) >36 dB. In addition, TS-DFB lasers with uniform reflection gratings are studied, and simulated results show that the modulation characteristic is far inferior to the laser with a phase-shifted grating reflector. [ABSTRACT FROM AUTHOR]

The tunable laser based on distributed feedback (DFB) laser array has a good single-longitudinal-mode property, high wavelength stability, narrow spectrum linewidth, and feasibility for monolithic integration. The tunable in-series DFB laser array (TIDLA) was proposed to avoid the large extra power loss by the optical combiner. But in the TIDLA, a large laser count will cause a large chip length, which brings about low utilization ratio of material, poor mechanical strength, and large power consumption. In this paper, we demonstrated a 4-channel TIDLA with duplex DFB sections. The total chip length was greatly shortened owing the duplexing of DFB sections. A long linearly chirped Bragg grating is implemented in the laser cavity to reduce the grating interference among different lasers. Multiple π phase shifts and two reflector sections are introduced to improve the mode stability. The designed channel spacing is 100 GHz, and the reconstruction-equivalent-chirp technique is used to provide high precision control of the grating phase. Noted that a variation of 0.1 nm in grating period will cause that of 0.65 nm in wavelength. Output power of above 4 mW, SMSR of above 42 dB, and small wavelength deviation of within 0.15 nm was obtained. Besides, fast channel switches of less than 1 μs are obtained by laser on/off switching. The proposed TIDLA might be applied in the NG-PON2 network where the dense wavelength division multiplexing technique and fast channel switching are required. [ABSTRACT FROM AUTHOR]

We present a new configuration of narrow linewidth semiconductor lasers (NLSLs) based on a novel narrow-band reflector (NBR) with π phase-shifted anti-symmetric Bragg grating (π-ASBG). Based on this configuration, two specific laser structures are theoretically analyzed. The effective length of Bragg grating is highly increased due to the double hybrid-mode resonances between the fundamental transverse electric (TE0) mode and first-order transverse electric (TE1) mode in the π-ASBG with the aid of a uniform grating reflector. The narrowest linewidth of ∼2.4 kHz is obtained of the proposed NLSLs, which is much lower than the traditional NLSLs with external uniform Bragg grating in the case of the same grating length. [ABSTRACT FROM AUTHOR]

Multi-wavelength distributed feedback laser array (DFB-MLA) based tunable semiconductor lasers have been widely used owing to the high mode stability and simple wavelength tuning scheme. In this paper, we proposed and experimentally demonstrated a matrix-grating tunable DFB laser array. And the reconstruction-equivalent-chirp (REC) technique is utilized to simplify grating fabrication and realize precise control of the grating phase. Traditionally, the laser is tuned by thermal-electric cooler (TEC), with large power consumption, slow wavelength tuning capability, and added device. To improve the wavelength tuning speed of laser, we varied laser’s injection current instead of adjusting TEC’s temperature. In addition, we analyzed the thermal influence of submount on the laser and then chose the SiO2 as the submount material for its low thermal conductivity and poor heat dissipation, resulting in wide wavelength tuning range via injection current. The DFB-MLA chip achieves a better tunable effect as the lasers can be tuned at 3.5–3.7 nm per channel from 50 to 120 mA with stable output power of over 3 mw as contrasted with the laser on the AlN submount being tuned at 1.4–1.5 nm per channel. And the chip has a side-mode suppressing ratio (SMSR) of over 35 dB and strong stability of wavelength in the repeated experiments. The proposed method may give a new way to realize the wide tuning range tunable DFB laser with a simple wavelength tuning mechanism in the future, especially for the applications of uncooled low-cost tunable lasers. [ABSTRACT FROM AUTHOR]

We propose a new kind of distributed feedback (DFB) semiconductor laser based on the sampled Moiré grating (SMG) integrated with a grating reflector (GR). Coupling coefficient along the laser cavity can be controlled, and $\pi $ phase shift ($\pi $ -PS) can be introduced by SMG. The GR, which is a uniform sampled grating, can provide light reflection instead of high reflection (HR) facet coating. Thus, the front and rear facets are both coated with anti-reflection coatings (AR/AR) to avoid the influence of random grating phase at the HR facet. Therefore, more output power, better single longitudinal mode (SLM) operation, and higher wavelength precision can be simultaneously achieved, compared with traditional DFB lasers with AR/HR facet coatings. As an example, an 8-channel DFB laser array based on the proposed structure has been simulated. The proposed laser may benefit the applications requiring both high output power and wavelength precision, such as wavelength division multiplexing (WDM) transmission systems and gas sensors. [ABSTRACT FROM AUTHOR]

A dual-frequency Doppler Lidar (DFDL) with high precision utilizing a monolithic integrated two-section DFB laser as the dual-frequency light source is proposed and experimentally demonstrated. The DFDL can be realized with smaller size using the monolithic integrated two-section DFB laser which is fabricated by the reconstruction-equivalent-chirp (REC) technique with high precision and low fabrication cost. The range of the measured speed is from 13.62 μm /s to 1.56 m/s, which covers 6 orders of magnitude. The largest relative error of the DFDL system is 3.16%. The DFDL system has an excellent resolution of 1.95 μm/s, which is suitable to detect micro speed changes. [ABSTRACT FROM AUTHOR]

We designed and fabricated a π equivalent phase-shifted sampled Bragg grating (SBG) semiconductor laser with a controlled distributed phase shift. The phase shift is equivalently realized with reconstruction-equivalent-chirp (REC) technique. The laser is divided into three sections with the same length. By injecting different currents into the side and middle sections, a distributed phase shift can be introduced. The lasing wavelength can be continuously tuned by the injection currents. In our experiment, when the total current keeps 130 mA, the lasing wavelength can be continuously tuned by 1.2 nm. During the tuning, the side mode suppression ratio keeps above 40 dB and the output power varies only 1.3 dB. Therefore, the proposed method provides an alternative solution for the multiwavelength laser arrays in dense wavelength-division multiplexing (DWDM) systems. [ABSTRACT FROM AUTHOR]

In this mymargin letter, we experimentally demonstrated a 1550-nm high-power single-longitudinal-mode (SLM) distributed feedback (DFB) semiconductor laser based on sampled moiré grating (SMG). By designing the sampling structure with micrometer scale, moiré grating (MG) can be equivalently realized along the laser cavity. Then, we can reduce the coupling coefficient near laser facet so as to increase the output power. The cavity length and ridge width of the fabricated laser are 1.0 mm and $3.0~\mu \text{m}$ , respectively. The measured threshold current and the slope efficiency are 30.0 mA and 0.36 mW/mA at the heat-sink temperature of 25 °C, respectively. When the injection current is 800.0 mA, the maximum output power is about 183.0 mW. The saturation power is significantly improved compared with conventional DFB laser with uniform sampled grating (USG), which was fabricated on the same wafer. In addition, a four-channel DFB laser array based on SMG was also fabricated on the same wafer, showing good wavelength uniformity. [ABSTRACT FROM AUTHOR]

A compact cascaded tunable distributed feedback semiconductor laser is proposed and theoretically analyzed. Each laser section (LS) is formed by two adjacent grating sections (GSs) with slightly different Bragg wavelengths and a $\pi $ phase shift in the joint between them. A step-wise grating period profile is designed to realize multi-channel lasing. Since two LSs share a common GS, the total cavity length of the tunable laser is significantly reduced. As an example, a tunable laser with six GSs and five $\pi $ phase shifts was designed and analyzed, resulting in a continuous tuning range of 12 nm. The total length of the laser is reduced by 40% compared with the conventional structure. Furthermore, an improved structure with apodized grating in each GS is also proposed. The single mode stability and fabrication tolerance are significantly improved. Due to the compact structure, the cost of the proposed laser can be highly reduced. Therefore, we think the proposed structure would benefit the practical applications to the low cost tunable lasers in wavelength-division multiplexing systems. [ABSTRACT FROM AUTHOR]

A novel microwave photonic filter (MPF) based on carrier-suppressed single sideband (CS-SSB) injected distributed feedback (DFB) laser is proposed. The proposed MPF system exploits the frequency selective gain feature of optical injected DFB lasers, which can be tuned by adjusting the optical injection parameters or the working conditions of the laser. Therefore, the proposed MPF system can be tunable. The proposed system is verified by a proof-of-concept experiment, and the results show that the passband of the proposed MPF can be tuned by tuning the injection ratio and bias current of the slave laser, where the tuning range of 9–39 GHz is realized. At the same time, the out-of-band rejection of the proposed MPF can reach to 32 dB. Moreover, a dual-passband MPF response is also realized by the proposed system with a couple of master lasers, and the two passbands can be tuned independently from 10 to 39 GHz. [ABSTRACT FROM PUBLISHER]

Based on the reconstruction-equivalent-chirp technique and tuning only by the injection current, a multisection DFB tunable laser is demonstrated experimentally. At the temperature of 20 °C, each laser can be tuned at about 3.4–3.6 nm with a side-mode suppressing ratio (SMSR) of over 35 dB from 30 to 170 mA, and the tuning speed is about 10–30 ms, which is much faster than that by the thermoelectric cooler. The results may help to realize very low cost tunable lasers in the future. [ABSTRACT FROM PUBLISHER]

A wideband frequency-tunable optoelectronic oscillator using four-wave mixing nonlinear dynamics of an optical-injected distributed feedback (DFB) semiconductor laser is proposed and experimentally demonstrated. Utilizing the wavelength-selective optical gain of the DFB laser under optical injection, a frequency-tunable microwave photonic filter is realized, which is used as the desired oscillation frequency selector. Therefore, the electrical bandpass filter is not required in the proposed scheme. An optoelectronic oscillating signal with a frequency tuned from 9.63 to 19.11 GHz is obtained by changing the injection parameters. The single sideband phase noise of the generated 13.74-GHz microwave signal is measured to be −103.19 dBc/Hz at 10-kHz offset. [ABSTRACT FROM PUBLISHER]

An asymmetric π equivalent phase shift sampled Bragg grating (SBG) semiconductor, which is consisted of two section with the same length but different sampling duty cycle 0.4 and 0.6, is investigated experimentally. By increasing the two injected currents of the studied laser from 15 mA to 120 mA, the lasing wavelength can be tuned by 2.1 nm. Combining selecting appropriate sampling period, the lasing wavelength of the laser can be tuned to meet the ITU-T standard. Because of high yield and low cost, this type of SBG laser is very beneficial for designing and fabricating monolithically integrated wideband multiwavelength laser array for photonic integrated circuits in next generation fiber-optic system. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:692-696, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27357 [ABSTRACT FROM AUTHOR]

Based on reconstruction-equivalent-chirp technology, an equivalent \lambda/4 phase shift was introduced into the center of an asymmetric sampled Bragg grating semiconductor laser that had two sections of the same lengths but different effective refractive indices. This structure could suppress the zeroth-order channel lasing effectively and enable the laser to operate in a single longitudinal mode with high stability. Such a method can also be used to fabricate a high-quality multiwavelength laser array for enhancing the yield efficiently at reduced cost. [ABSTRACT FROM AUTHOR]

A distributed feedback (DFB) semiconductor laser with three phase shifts based on reconstruction equivalent chirp (REC) technology is proposed and investigated numerically. With the combination of multiple phase shifts and corrugation pitch modulated (CPM) structure, we also propose a novel and more complex structure named dual CPM, which has a flatter light power distribution along the laser cavity compared with the true double phase shifts DFB laser diode (LD), while the P-I curves are nearly the same. The proposed dual CPM structure is also designed and analyzed based on REC technology. The simulation results show that, the DFB semiconductor laser with complex structure such as phase shifts, or even arbitrary variation of the grating period can be achieved equivalently and easily by changing the sampling structure. But its external characteristics are almost the same as those DFB lasers with true phase shifts, or true arbitrary variation of the grating period. The key advantage of the REC technology is that it varies only the sampling structure and keeps the seed grating (actual grating in sampling structure) period constant. So its fabrication needs only low-cost and standard holographic exposure technology. Therefore we believe this method can achieve the high-end and low-cost DFB LD for mass production. [ABSTRACT FROM AUTHOR]

A wideband tunable single bandpass microwave photonic filter (MPF) based on the four‐wave mixing (FWM) nonlinear dynamics of a distributed feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. Utilising the wavelength‐selective optical gain of the optical‐injected DFB laser, phase‐modulation to intensity‐modulation conversion is obtained, leading to the realisation of a single bandpass MPF. By changing the injection parameters, an MPF with a frequency tuning range of 27.72 GHz has been achieved. The minimum 3 dB bandwidth and the out‐of‐band suppression ratio are measured to be 61.2 MHz and 25 dB, respectively. [ABSTRACT FROM AUTHOR]

A directly-modulated Fourier domain mode-locked optoelectronic oscillator (FDML_OEO) based on three-section mutual-injection integrated semiconductor laser (TS_MIISL) with dual-loop feedback structure is proposed and experimentally demonstrated in this paper. By driving the TS_MIISL to work under the period-one (P1) state and modulating the TS_MIISL with low-repetition-rate sawtooth drive signal, a linear frequency-modulated (LFM) signal can be generated. Through adjusting the delay time of the feedback loops to match with the time duration of drive signal, the LFM signal can be significantly optimized in terms of spectral purity. In such a proposed FDML_OEO, no external modulator, polarization controller (PC) and filter are utilized, leading to an outstanding advantage in terms of stable performance and compact structure. The high-purity LFM signal with center frequency and bandwidth of 14 GHz and 8 GHz is obtained. The maximum time-bandwidth product (TBWP) of generated LFM signal could reach up to 48800. Due to the introduction of dual feedback loop, the frequency comb contrast and linewidth could reach up to 45 dB and 5 kHz, respectively. The center frequency and bandwidth of the generated signals are both tunable. A demonstration is made to prove that the pre-compensation processing could improve the linearity of LFM signals. • We have also proposed an equivalent microwave photonics filter (MPF) and it can be observed when the TS_MIISL works at P1 state. • Because of the short distance of PS between the FL and RL, the TS_MIISL would go into the short-coupling regime. • When the delay matching is completed, the spectral purity of the obtained LFM signal is significantly optimized by the optoelectronic feedback loop. • When the delay matching is completed, the spectral purity of the obtained LFM signal is significantly optimized by the optoelectronic feedback loop. [ABSTRACT FROM AUTHOR]

The tunable distributed feedback (DFB) semiconductor lasers with cascaded configuration were designed and fabricated using equivalent phase shift (EPS) technique. 32-wavelength division multiplexing (WDM) channels with 50-GHz and 100-GHz wavelength spacing were experimentally demonstrated. In such a tunable laser, single mode operation can be ensured by introducing EPS and the wavelength tuning can be realized by cascaded sections with specific sampling periods combining with chip heating. The proposed approach has some advantages such as good single mode property, low fabrication cost and feasibility of monolithic integration. The experimental results show that the tuning range can be nearly up to 25 nm and the side mode suppression ratios (SMSRs) of most channels are above 40 dB. The proposed laser should be promising for cost-effective applications in WDM systems. [ABSTRACT FROM AUTHOR]

Abstract: The phase-shifted distributed feedback (DFB) semiconductor laser with linearly chirped grating based on reconstruction equivalent chirp (REC) technique is theoretically analyzed and experimentally demonstrated for the first time. The asymmetric property of the lasing spectrum is analyzed according to the normalized threshold gain, and the different spectra from each facet of the laser are compared. Due to the low cost and fabrication flexibility, REC technique provides a promising way for the future practical applications of DFB lasers with chirped gratings. [Copyright &y& Elsevier]

Abstract: Experimental results of corrugation-pitch-modulated (CPM) DFB lasers with distributed phase shift (DPS) based on reconstruction-equivalent-chirp (REC) technique are demonstrated. The DPS can flatten the light intensity distribution along the laser cavity and reduce the spatial hole burning (SHB). The lasers have good single longitudinal mode (SLM) property even under high injection current. Thanks to the sampling technique, the grating can be easily fabricated by holographic exposure and conventional lithograph. [Copyright &y& Elsevier]

Abstract: A λ/4 phase-shifted distributed feedback (DFB) semiconductor laser with a preformed chirped grating used to compensate the spatial hole burning (SHB) induced index change is proposed and analyzed. It shows that compared with the three phase shifted DFB laser which is known for its good performance to eliminate SHB, the proposed SHB compensated laser has better single longitudinal mode property, narrower spectral linewidth and better dynamic characteristics. [Copyright &y& Elsevier]

Abstract: An apodized DFB semiconductor laser based on reconstruction-equivalent-chirp (REC) technology is proposed and investigated numerically. By changing the duty cycle of the sampling period, the magnitude of the equivalent index modulation is varied. Thus the equivalent apodization is introduced instead of an actual apodization. This novel DFB structure is advantageous in that it can enlarge the threshold gain difference and improve the mode stability compared with the conventional DFB laser. Moreover, the structure can be easily fabricated by standard holographic technology instead of high cost Electron-beam lithography. [Copyright &y& Elsevier]