To evaluate the effect of crosstalk caused by wavelength deviation of reconstruction-equivalent-chirp (REC) integrated multi-wavelength laser arrays (MWLAs) on an optical free-space communication system in which wavelength division multiplexing (WDM) is applied, we derive the model of power penalty caused by the wavelength deviation of REC-MWLAs and the bit error rate (BER) of the system under atmospheric turbulence and conduct a numerical simulation. The two adjacent channels in arranged REC laser arrays are defined as the analysis scope. We find that the power penalty is more sensitive to the deviation of the channel itself than the adjacent channel as the frequency shift increases from 0 to 50 GHz. The numerical relationship between the BER and power penalty is drawn to further investigate the tolerance for wavelength deviation under the requirements of BER < 10 − 6 and BER < 10 − 9. In addition, for a smaller deviation of 5 GHz of the analyzed channel, the linewidth compression of the REC laser can decrease the power penalty from 1.3 to 0.7 dB, improving the system performance and moderating the demands for deviation of REC-MWLAs, and the gemination of channel spacing does not evidently reduce the requirement for deviation. The results of this work demonstrate the feasibility of REC-MWLAs as the light source of WDM free-space communication systems under atmospheric turbulence and provide an effective reference for the allowable deviation in the design and testing of MWLAs.
We propose a design of a bandpass-filter-integrated metalens for the gas sensing. A device with both filtering and focusing functions is designed, by integrating a one-dimensional photonic crystal and a metalens. It has a great filtering effect for one absorption peak (1650 nm) of the target gas (the methane). The transmission rate of the target wavelength is 89% and the relative intensity of the light field is up to 135. Our device has the function of focusing the light onto the photodetector (PD). The response of PD has been greatly improved. Meanwhile, the device can be fabricated into a photonic integrated chip. We provide a new scheme of the photonic integration chip for the multiple gas sensing.
Multi-wavelength laser arrays are critical for co-packaged optical interconnects, dense wavelength division multiplexing, high-performance optical computing, and sensors. Based on the reconstruction equivalent chirp (REC) technique, multiwavelength laser arrays (MLAs) are demonstrated with high channel count and high precision wavelength spacing. Recently, the photonic wire bonding (PWB) technique is applied to connect the MLA. But the lasers are mostly surface-emitted, such as the horizontal cavity surface-emitting lasers. In the practical applications, the lasers are usually edge-emitted, which is more difficult for the PWB technique. By using the photonic wire bonding technique, we connected a six-channel REC-based MLA, a PLC chip, and the fiber array. The lowest total transmission loss reaches to 7.8 dB. With further optimization of the PWB waveguide, the REC-based MLAs can be applied more easily, which is a potential solution for the requirement of high performance multi-wavelength light source in the relevant field.
By expanding the reconstruction-equivalent-chirp (REC) technique into two-Dimensional (2D) grating, we designed a three-wavelength mode converter with three-cascaded tilted sampled Bragg gratings (3C-TSBG). Theoretical simulation results show that the presented 3C-TSBG can realize three-wavelength conversion between the fundamental transverse electric mode (TE0) and the first-order transverse electric mode (TE1). In addition, the mode-conversion wavelength can be tuned by changing the period and tilted angle of the cascaded sampled gratings. More importantly, compared with the cascaded tilted Bragg gratings (C-TBG), the 3C-TSBG can improved the error tolerance and wavelength control accuracy. Therefore, the proposed 3C-TSBG has potential applications in reconfigurable mode-division-multiplexing communication systems and other areas where programmable mode conversion is required.
We have experimentally demonstrated a 16-wavelength high-power DFB laser array with 200 GHz (1.6 nm) channel spacing based on the asymmetric equivalent π phase shift. Good single-longitudinal-mode (SLM) operations are obtained by introducing asymmetric equivalent π phase shifts. The effect of random phase on the high-reflective (HR) coating facet also is weakened by introducing asymmetric equivalent π phase shifts which are implemented at the 1/5 laser cavity close to the facet with HR coating. The average channel spacing is 1.62 nm, which deviated 0.02 nm from our design under the same injection current (300 mA) of each laser. The output power of 16 channels is above 100 mW at the bias current of 400 mA and the average slope efficiency is 0.41 W/A at 25 °C. Good single-longitudinal-mode are obtained for all the 16 channels with side mode suppression ratios of above 50 dB. Besides, the relative intensity noise at an injection current of 200 mA is below -157 dB/Hz.
We propose and theoretically analyze a DFB semiconductor laser monolithically integrated with anti-symmetric Bragg grating (ASBG) modulator. A π phase shifted Bragg grating with single-mode ridge waveguide and an ASBG with multimode waveguide supporting the fundamental transverse electric (TE0) mode and the first order transverse electric (TE1) mode, are joined by a tapered waveguide. After adding a phase shift section between the taper and ASBG, the electro-optical (E/O) response of ASBG modulator increases by 37.9% compared to the normal Bragg grating modulator (BGM), and becomes sensitive to the effective refractive index change of the straight waveguide. The proposed integrated device can be applied in sensing.
Recent advances in monolithically integrated multi-section semiconductor lasers (MI-MSSLs) have propelled microwave photonic technologies to new potentials with a compact, reliable, and green implementation. Much research has examined that MI-MSSLs can realize the same or even better microwave photonic functions compared to discrete lasers by taking advantages of enhanced light–matter interactions. They are beneficial towards the future of integrated microwave photonics (IMWP) once integrating the other optical components such as modulators, amplifiers, transmission waveguide and so on. Herein, these recent advances in this emerging field are reviewed and discussed. Three main kinds of MI-MSSL structures are demonstrated including passive feedback laser, active feedback laser, as well as monolithically integrated mutually injected semiconductor laser. Their pros and cons are distinguished and compared through analyzing the desired characteristic indicators in modern MWP subsystems. The focus of this paper is on the photonic microwave techniques based on the nonlinear dynamics of MI-MSSLs, consisting of electro-optic conversion characteristics enhancement, photonic microwave generation, microwave photonic filter, as well as multiwavelength laser array for wavelength division multiplexing radio-over-fiber (WDM-RoF) networks. We also take a look at the future prospective at the research directions and challenges in this area.
Tilted Bragg grating (TBG) has been intensively investigated for photonic devices such as fiber sensors and on-chip filters. In this paper, we present that TBG can be equivalently realized by designing tilted sampled Bragg grating (TSBG), which is formed by superimposing the pre-designed tilted sampling structure on the basic grating. Since the basic grating is uniform and the sampling structure is in the order of micrometer, the fabrication of TSBG can be realized with one step of holographic exposure combined with another step of micro-lithography. We designed and simulated the equivalent light responses of the TSBGs as that of the target TBG in the photonic devices. As examples, a mode converter based on TSBG has been proposed, which can be used for add-drop filter in the wavelength division multiplexing (WDM) technology combined with mode division multiplexing (MDM) technology. We also investigate the core-to-cladding mode coupling of TSBG in single-mode fiber for fiber sensing as well as the spatial filter in the α- DFB laser. The proposed technique may pave a new way for different 2D gratings with good design flexibility and easy fabrication in various photonic devices.
This paper presents our recent studies on photonic devices based on antisymmetric Bragg gratings (ASBGs). ASBGs can realize backward mode conversion between the fundamental and first order transverse electric mode, i.e., TE0 and TE1. If a π phase shift is inserted in the middle of ASBG, light resonance along with mode conversion can be set up. We call this new resonance as the “Hybrid mode resonance”. Based on this structure, several photonic devices are realized. For example, we experimentally demonstrated an on-chip light filter with dropped reflected light. It can be equivalent to the light circulator in some cases and benefits the application to photonic integrated systems. Besides, other photonic devices such as single wavelength resonator and narrow band reflector are also realized. We think the proposed grating structure may give a new way to design high-performance photonic devices.
We propose a silicon modulator in a multi-mode waveguide based on the anti-symmetric Bragg grating (AS-BG). When the incident light is in the fundamental transverse electric (TE0) mode, the reflected light of the AS-BG is in the first order transverse electric (TE1) mode, rather than the TE0 mode. Therefore, the reflected TE0 mode is radiated in a tapered waveguide (WG) that connects a multi-mode and single-mode WG. As a result, the back reflection of the Bragg grating (BG) based silicon modulator avoids the utilization of an optical circulator, especially when ingrating with a semiconductor laser, which is susceptible to the external light.
We propose an on-chip optical narrowband reflector (NBR) based on two cascaded Bragg gratings (BGs). A π phase shifted anti-symmetric Bragg grating (π-PS-ASBG) and a rear uniform Bragg grating (UBG), are in-line connected. The π-PS-ASBG provides a hybrid mode resonance between the even- and odd TE (TE0 and TE1) modes, while the UBG is used as a rear reflector to reflect the TE0 mode that transmitted from the π-PS-ASBG. The reflection bandwidth decreases when the coupling coefficient increases, which is different from traditional UBG. The performances are theoretically studied via both the rigorous three-dimensional finite-difference time-domain (3D-FDTD) method and multimode transmission matrix method (MTMM). The calculated 3-dB bandwidth is 0.16 nm when the whole grating length is 400 μm (π-PS-ASBG: 200 μm and UBG: 200 μm) and the coupling coefficients of the π-PS-ASBG and rear UBG are 240cm-1 and 110cm-1, respectively. The proposed NBR can be applied in the cases requiring narrow reflection such as narrow linewidth semiconductor lasers.
In recent years, with the development of eavesdropping technology, how to improve the security of data transmission has become a hot research issue. In order to enhance the security of the secure communication system, a chaotic laser secure communication system with variable laser power is proposed in this paper. Based on the original optoelectronic feedback chaotic laser communication system, the change of laser power is regarded as a new key. The simulation results show that the error rate of the eavesdropper is above 10-2 over most of the laser power, and the average error bit rate of the eavesdropper is 7 orders of magnitude higher than the average error rate of the authorized receiver. In addition, the appropriate masking efficiency will reduce the bit error rate of the eavesdropper, while it has little effect on the eavesdropper. The system scheme can be used in communication with high confidentiality requirements in the future.
A compact cascaded tunable distributed Bragg reflection (DBR) semiconductor laser is proposed and simulated. Each laser section (LS) is formed by two passive adjacent grating sections (GSs) with slightly different Bragg wavelengths and an active section (AS) between them. A step-wise grating period profile is designed to realize wide range 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 four GSs and three ASs was designed and analyzed, resulting in a continuous tuning range of 13.2 nm. Furthermore, an improved structure with apodized grating in each GS is proposed for good single mode property. The single mode stability and fabrication tolerance are significantly improved. Particularly, this structure based lasers has a fast switching speed of about 5ns. The proposed structure would benefit the practical applications to the low cost tunable lasers in wavelength division multiplexing (WDM) systems.
High-quality microwave generation and frequency up-conversion are demonstrated utilizing a photonic integrated two-section DFB laser. Both the DFB lasers are fabricated by the reconstruction-equivalent-chirp (REC) technique. We acquire microwave signals by optical heterodyne. High-quality microwave signal can be generated by the optical injection locking technique with low phase noise of -96.3 dBc/Hz at 10-kHz and narrow linewidth of a few kHz level. Besides, Frequency-doubled and frequency-quadrupled signals are achieved respectively.
We designed and experimentally studied a sampled Bragg grating semiconductor laser with π equivalent phase shift (EPS) and three equally separated electrodes. When the central electrode is injected different current from the other electrodes, a distributed phase shift (DPS) can be introduced into the studied laser. By changing the injection current ratio into three electrodes, the DPS can be controlled and then the lasing wavelength can be tuned while the laser keeps single longitudinal mode operation.
Reconstruction equivalent chirp (REC) technique is widely used in the design and fabrication of semiconductor laser arrays and tunable lasers with low cost and high wavelength accuracy. Bent waveguide is a promising method to suppress the zeroth order resonance, which is an intrinsic problem in REC technique. However, it may introduce basic grating chirp and deteriorate the single longitudinal mode (SLM) property of the laser. A nonlinear equivalent chirp pattern is proposed in this paper to compensate the grating chirp and improve the SLM property. It will benefit the realization of low-cost Distributed feedback (DFB) semiconductor laser arrays with accurate lasing wavelength.
We studied the in-line DFB tunable laser based on REC technique. We mapped the contour lines of the P-I contour diagram of this in-line tunable laser into the wavelength-current contour map. And the maximum output power is obtained.
Also the tuning currents are obtained. Firstly, we simulated the P-I contour as well as wavelength-current contour. Secondly, we experimentally demonstrated the mapped
contour.
A dual-wavelength laser array is obtained by two asymmetric phase shifts. Different wavelength spacings are obtained by varying the magnitude of the phase shifts. The phase shifts are distributed along two phase-arranging regions, which are obtained equivalently by specially-designed sampled structures with uniform seed gratings.
A laser array, which is consisted of 56 π equivalent phase shift (EPS) sampled Bragg grating (SBG) semiconductor laser, is experimentally investigated. The experimental results show the influence of the sampling duty cycle fabrication error on the lasing wavelength of an SBG semiconductor laser can be ignored.
A corrugation-pitch-modulated (CPM) distributed feedback (DFB) semiconductor laser based on
reconstruction-equivalent-chirp (REC) technology is first experimentally demonstrated. The laser can suppress
spatial hole burning (SHB) effectively and operates in good stable single longitudinal mode even the injection
current very high.
A distributed feedback (DFB) semiconductor laser with multiple phase shifts based on reconstruction equivalent chirp
(REC) technology is numerical studied and fabricated. The simulation results show that the performances of the multiple
phase shifts DFB semiconductor laser based on REC technology are nearly the same as the actual multiple phase shifts
DFB laser. They have the same P-I curves, the internal power distributions and the output ASE spectra. However, it only
changes the sampling structures of the REC based laser with the uniform seeding waveguide grating. So the fabrication
of such laser is very easy. In this paper, the fabrication of this structure was realized for the first time to the best of our
knowledge. The experimental results show that it has good single longitudinal mode operation even under high injection
current with side mode suppression ratio (SMSR) above 55dB even at high injection current.
Based on a special sampling technique, we present a special structure for distributed feedback (DFB) lasers. As a
conventional equivalent π phase-shift sampling Bragg grating (SBG), this proposed structure also introduces an
equivalent π phase-shift into both its ±1st order channel. Combined with the conventional equivalent π phase-shift, the
sampling technique can be used to design and fabricate multiwavelength semiconductor or fiber lasers conveniently.
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