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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]

A method of engineering spectrum of mode converter based on cascaded Bragg gratings is investigated in detail. Due to the cascaded structures, the proposed mode converter owns higher design degrees of freedom comparing with mode converter based on traditional Bragg grating. Meanwhile, thanks to various light responses of gratings, conversion spectrum can be easily tailored by designing grating structures. As examples, mode converters with specific conversion spectra such as single-band pass, double-band pass, multi-band pass, narrow-band backward spectra have been designed. Besides, the same triangle-shaped band pass spectrum is obtained by two converters based on different grating structures with the aid of distribute-layer-peeling algorithm, which further shows the high design flexibility of the proposed method. We think the proposed method gives a new way for advanced mode converter with required conversion spectrum. [ABSTRACT FROM AUTHOR]

We proposed a new kind of add-drop multiplexer based on $\pi $ phase-shifted antisymmetric Bragg grating ($\pi $ -ASBG). Light resonance is formed in the $\pi $ -ASBG with mode conversion between backward fundamental transverse electric (TE0) mode and the forward first order transverse electric (T1) mode. With the aid of the TE1 mode generated in the $\pi $ -ASBG, add-drop multiplexer can be designed. As examples, two multiplexer structures based on single- and dual-bus resonator, on silicon-on-insulator (SOI) platform have been studied in detail. Besides, no light is reflected to the input port, if the structure is carefully designed with critical coupling condition satisfied. For the fabricated add-drop multiplexer based on single-bus resonator, the extinction ratio is 23.90 dB and full width at half maximum (FWHM) is 0.33 nm at the through port. For the fabricated add-drop multiplexer based on dual-bus resonator, the extinction ratio is 17.22 dB and FWHM is 0.29 nm at through port. The results show that proposed structures provide a new method to realize add-drop multiplexer and other integrated optical filters for optical communications and sensors. [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]

We propose and theoretically analyze a hybrid transverse mode resonance DFB semiconductor laser which consists of one active section with π-phase shifted anti-symmetric Bragg grating (π-ASBG) and two passive sections with uniform Bragg grating. The hybrid light resonance along with mode conversion between the fundamental transverse electric (TE0) mode and first order transverse electric (TE1) mode is formed by the π-ASBG. The emitted light from one facet with the TE0 or TE1 mode can be controlled by tuning the injection currents of the passive sections. As an example, a laser with ridge waveguide is designed and simulated. The transverse mode with the same wavelength is tuned by changing the injection currents of the passive sections. The suppression ratio between the two transverse modes reaches 18.4 dB and 18.7 dB when the TE0 and TE1 modes are emitted, respectively. A simple method for equivalently realizing the grating in the proposed laser was also analyzed. Therefore, as the transverse mode tunable light source, the proposed laser may benefit the future mode division multiplexing (MDM) systems for reconfigurability and more flexibility. [ABSTRACT FROM AUTHOR]

The principle, design, and characterization of a resonator on the silicon-on-insulator (SOI) platform based on the $\pi $ phase-shifted antisymmetric Bragg grating (ASBG) are presented. With the aid of an asymmetric directional coupler (ADC), the resonance circuit between the two ASBGs is formed by the forward first-order transverse electric (TE1) mode and the backward fundamental transverse electric (TE0) mode. Only negligible amount of the backward TE0 mode can be coupled to the bus waveguide, which is different from the conventional Fabry–Perot (F-P) resonator. Compared with the widely used microring resonator, it can realize single wavelength resonance. The single resonance resonator with an extinction ratio of 20.0 dB and a quality factor (${Q}$ -factor) of 9888 has been experimentally demonstrated. Moreover, multiple wavelength resonances with a free spectrum range (FSR) of 0.63 nm is obtained when the phase shifter length is $200~\mu \text{m}$. [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]

In this letter, we provided a proof-of-concept study on the anti-symmetric sampled Bragg grating (ASBG) with $\pi $ equivalent phase shift ( $\pi $ -EPS) in silicon-on-insulator (SOI). A four-channel narrow-band passive filter array was fabricated. Experimental results show that the 0th-order resonance is totally eliminated, while the +1st-order resonance is maintained. In addition, 3-D finite-difference-time-domain (3-D-FDTD) algorithm was also used to analyze the other characteristics of this structure, such as the radiation phenomenon caused by anti-symmetric feature. Since the anti-symmetric basic grating combined with sampling pattern could equivalently realize various grating structures, ASBG can be used for multi-wavelength photonic devices, such as DFB laser array, sensor array, electro-optic modulator array, and so on. [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]

We have developed and demonstrated a novel technique to manufacture large bandwidth grating with a nearly arbitrary transmittivity profile. The technique is based upon scanning the large chirped phase mask and controlling of the reflective index modulation distribution along the grating length. [Copyright &y& Elsevier]

The grating-assisted contra-directional coupler (contra-DC) is one of the commonly used add-drop filters serving for coarse wavelength-division-multiplexing (CWDM) systems due to its flat-top and wide-band response. However, the free-spectral-range (FSR) of contra-DC is limited by the back reflection to the input port caused by the intra-waveguide coupling. In this paper we propose an anti-reflection grating-assisted contra-DC by simply increasing the sidewall corrugation width. The intra-waveguide coupling coefficient can be decreased to 0 when the corrugation width is increased to a certain value. The simulation result shows that the transmission at drop port is −0.42 dB, while the back reflection to the input port is only −22.0 dB. The 4-channel cascaded contra-DCs with wavelength range of ∼60 nm are also simulated, all the channels are not affected by the intra-waveguide coupling. We believe the proposed contra-DC with large corrugation width can be applied to the CWDM system requiring a broad spectrum range. • Explanation of the vanish of stopband when the corrugation width of waveguide Bragg grating is large. • Proposing an anti-reflection grating-assisted contra-directional coupler by simply increasing the corrugation width. • High suppression of intra-waveguide reflection in the grating-assisted contra-directional coupler of 22.0 dB. [ABSTRACT FROM AUTHOR]

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]