Reconstruction-equivalent-chirp Research Articles

Highly-reflective facet-coated multi-wavelength DFB laser array with exact wavelength spacings.

A distributed feedback (DFB) laser array of twenty wavelengths with highly reflective and anti-reflective (HR-AR) coated facets is both theoretically analyzed and experimentally validated. While the HR facet coating enhances high wall-plug efficiency, it inadvertently introduces a random facet grating phase, thereby compromising the lasing wavelength's predictability and the stability of the single-longitudinal-mode (SLM). In this study, two key advancements are introduced: first, the precisely spaced wavelength is achieved with an error of within ±0.2 nm using the reconstruction-equivalent-chirp (REC) technique; second, the random grating phase on the HR-coated facet is compensated by a controllable distributed phase shift through a two-section laser structure. The SLM stability can be improved while the wavelength can be continuously tuned to the standard wavelength grid. The overall chip size is compact with an area of 4000 × 500 µm2. The proposed laser array has a light power intensity above 13 dBm per wavelength, a high side mode suppression ratio above 50 dB, and low relative intensity noise under -160 dB/Hz. These attributes make it apt for deployment in DWDM-based optical communication systems and as a light source for optical I/O.

Research on an Enhanced Detuned-Loading Effect in Integrated Two-Section DFB Lasers with High Modulation Bandwidths.

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.

10×10 Gbs directly modulated DFB laser array based on the REC technique.

We proposed and experimentally demonstrated a directly modulated distributed feedback (DFB) laser array with a transmission rate of 100Gbps (10c h a n n e l s×10G b p s). The grating design is based on the reconstruction equivalent chirp (REC) technique, which enables precise control of the channel wavelength spacing to 100GHz, as specified in the ITU-DWDM standard. DFB laser arrays incorporating the REC technique demonstrate excellent consistency performance, with a side-mode suppression ratio exceeding 48dB, threshold current of approximately 20mA, and modulation bandwidth of greater than 13GHz at a bias current of 100mA. We evaluated the laser's performance by loading a 10Gbps nonreturn-to-zero signal onto the laser using direct modulation and transmitting it over a 10km single-mode fiber. Based on our experimental results, the proposed DFB laser array is promising to be utilized in the next generation of low-cost, 100Gbps DWDM communication systems.

High-speed directly modulated distributed feedback laser based on detuned loading and photon–photon resonance effect

A monolithic integrated two-section distributed feedback (TS-DFB) semiconductor laser for high-speed direct modulation is proposed and analyzed theoretically. The grating structure of the TS-DFB laser is designed by the reconstruction-equivalent-chirp (REC) technique, which can reduce the manufacturing cost and difficulty, and achieve high wavelength controlling accuracy. The detuned loading effect and the photon–photon resonance (PPR) effect are utilized to enhance the modulation bandwidth of the TS-DFB laser, exceeding 37 GHz, while that of the conventional one-section DFB laser is only 16 GHz. When the bit rate of the non-return-to-zero (NRZ) signal reaches 55 Gb/s, a clear eye diagram with large opening can still be obtained. These results show that the proposed method can enhance the modulation bandwidth of DFB laser significantly.

Wideband tunable REC-DFB laser array using thin-film heaters on the submount

A wideband wavelength-tunable 4×5 distributed feedback (DFB) semiconductor laser array based on the reconstruction-equivalent-chirp (REC) technique using a simple tuning scheme is demonstrated. It consists of 20 DFB lasers with 4×5 matrix interleaving distributions, two-level cascaded Y-branch optical combiners, and one active semiconductor optical amplifier (SOA), all in-series integrated on one chip. Unlike the traditional thermal-electric cooler (TEC)-based wavelength-tuning scheme, the tunable 4×5 REC-DFB laser array achieves a faster and broader continuous wavelength-tuning range using TaN thin-film heaters integrated on the AlN submount. By changing the injection current of the TaN resistor from 0 to 190 mA, the proposed tunable laser achieves a wavelength-tuning range of ∼2.5 nm per channel and a total tuning of over 50 nm. This study opens up new avenues for realizing cost-effective and wide-tuning-range semiconductor lasers.

Nanosecond tunable laser for the all-optical switching network.

The optically switched network can offset the increasing gap between datacenter traffic growth and electrical switch capacity due to the slowdown of Moore's law. Ultra-high-speed wavelength tunable lasers are especially vital for the high integration and performance improvement of the all-optical switching system. In this paper, a fast tunable laser based on a laser array is realized. The 2×8 matrix structure of the laser array is fabricated by the reconstruction-equivalent-chirp (REC) technique. Aiming at the 2×8 array, a drive control system is designed to provide stable and fast switching, to achieve high-speed switching of the laser wavelength, and to keep the wavelength stable after switching. The simulation and experimental results show that the switching time between any two wavelength channels of the laser is less than 10ns. The switching time of any two channels of the laser can be reduced by 2-3ns after the pre-emphasis processing of the electrical signal.

Modulation Bandwidth Enhancement and Frequency Chirp Suppression in Two-Section DFB Laser

We demonstrate a two-section distributed feedback (DFB) laser for direct modulation based on the reconstruction equivalent chirp (REC) technology. The two-section DFB laser exhibits a stable single-mode characteristic. Utilizing the photon-photon resonance (PPR) effect and detuned-loading effect, the 3-dB modulation bandwidth of the two-section DFB laser is improved from 8 GHz to 23 GHz. A 25 Gb/s non-return to zero (NRZ) signal is applied to the two-section DFB laser and eye diagrams with large open extent are obtained. In addition, the relative intensity noise is reduced to below −143 dB/Hz. The frequency chirp is also suppressed. The chirp parameter is reduced from 5.67 to 1.37, which is a small value in directly modulated DFB laser. We compared the eye diagrams after transmitting different distances, the results show that the two-section structure reduces the frequency chirp significantly. The modulation of the two-section DFB laser also has good linearity, with a 1-dB compression point of more than 18 dBm.

Tunable Laser via High-Density Integration of DFB Lasers With High Precision Wavelength Spacings

Fast optical switches have the potential of lowering the cost, power, and latency of today’s data-center networks. The on-off switching of DFB lasers in arrays is poised to provide extremely fast switching because the on-off time of a DFB laser is the level of sub-nanosecond. However, the key of the DFB laser array based tunable laser lies in the high precision control of the lasing wavelength. In this letter, we proposed and experimentally demonstrated a tunable laser by integrating 16 DFB lasers based on the reconstruction-equivalent-chirp (REC) technique. Without using the conventional e-beam lithography, an equivalent <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /4 phase-shift is fabricated in each DFB laser to ensure the single-longitudinal-mode (SLM) yield. Moreover, high precise wavelength spacing is realized. Wavelength deviations of 89.3% DFB lasers are within ±0.2 nm. The output power of all the channels is above 7 mW, and the relative intensity noise is below −130 dB/Hz. By on-off switching the lasers, sixteen channels with 2.4-nm spacing can be fast switched. The switching time between any two channels is less than 50 ns. In addition, a wide-band continuous wavelength tuning range of 38.4 nm can be obtained with a small temperature variation of 18 °C. Owing to the REC technique, the tunable laser via high-density integration of DFB lasers is demonstrated with simple fabrication, high SLM yield, and high wavelength precision, which opens up a path for wide-band and especially fast tunable lasers.

A Stable Dual-Wavelength DFB Semiconductor Laser With Equivalent Chirped Sampled Grating

A monolithic integrated dual-wavelength DFB semiconductor laser is fabricated and experimentally demonstrated. Utilizing the reconstruction-equivalent chirp (REC) technique, dual-wavelength lasing is obtained by introducing two symmetric equivalent phase shifts in a chirped sampled Bragg grating. The laser operates at 1650 nm and the wavelength spacing is about 0.8 nm at room temperature. The frequency of the beat signal between the two wavelengths is 88.47 GHz, and the linewidth of the beat signal is 5.1 MHz. Based on the REC technique, the grating pattern can be fabricated by using holographic exposure combining with conventional lithography. This work provides a simple and cost-effective way to achieve dual-wavelength semiconductor laser.

Enhanced Tuning Performance of In-Series REC-DFB Laser Array

In this study, a tunable in-series multi-wavelength distributed feedback laser array (DFB-MLA) based on reconstruction-equivalent-chirp (REC) technique with simple wavelength tuning scheme is presented and experimentally demonstrated. Unlike traditional DFB laser tuned by thermal-electric cooler (TEC), the proposed laser tuned by injection current can realize faster wavelength-tuning and reduce TEC power consumption. By comparing the thermal influence of different structures of heatsink blocks, several optimized block structures are selected for appropriate thermal conductivity and controllable heat dissipation, resulting in a broad and continuous wavelength tuning range. The proposed in-series DFB-MLA on optimized heatsink achieves better tuning performance with a wavelength tuning range of ~2.4 nm per channel from 40 to 120 mA and stable output power of over 20 mW compared to the laser mounted on the standard heatsink block with the tuning range of 1.4 nm per channel. Furthermore, the tunable laser keeps good single-mode stability, with a side mode suppressing ratio (SMSR) of over 40 dB. Thus, this study provides a new perspective for designing a low-cost continuous tunable semiconductor laser with a simple tuning mechanism in the future.

Research on the Asymmetric Corrugation-Pitch-Modulated HR-AR DFB Lasers With Sampled Gratings

A distributed feedback (DFB) laser for high-speed modulation with asymmetric corrugation-pitch-modulated (ACPM) grating structure and high-reflection and anti-reflection coating (HR-AR) coating is demonstrated theoretically and experimentally in this paper. The ACPM gating structure is fabricated by the reconstruction equivalent chirp (REC) technology, which is with low cost. The impact of the longitudinal spatial hole burning (LSHB) effect and the facet phase on the characteristics of the ACPM DFB laser is discussed in detail. The numerical simulation results show that the proposed ACPM DFB laser can suppress the LSHB effect significantly. Comparing with the conventional HR-AR DFB laser, the ACPM DFB laser can achieve higher output efficiency, better single-mode yield, and wider modulation bandwidth. The modulation eye diagrams of HR-AR DFB lasers with different grating structures are also presented. The experimental results show that the LSHB effect in the HR-AR DFB laser with ACPM structure is suppressed effectively. The laser with ACPM structure fabricated by the REC technique has high slope efficiency, stable single longitudinal mode operation, and wide modulation bandwidth.

A hybrid silicon evanescent laser with sampled Bragg grating structure based on the reconstruction equivalent chirp technique for silicon photonics

In this paper, we report on a direct bonding hybrid silicon evanescent laser with sampled Bragg grating structure based on the reconstruction equivalent chirp (REC) technique for the first time. By the design of the REC technique, the hybrid silicon evanescent laser in the +1st order channel is emitted. The optical mode is evanescently coupled between the III and V waveguide and silicon waveguide. A laser with 24 mA threshold current and 0.3 mW output power from silicon waveguide at 50 mA under the continuous wave operation is obtained.

Improved Range Tunability of DFB Lasers Based on REC Technique Under Injection Current

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 SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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.

The Investigation of the Balanced Output Power of Multi-Section Tunable Laser Based On Reconstruction-Equivalent Chirp Technique

A method to get balanced output power of a current-controlled in-line semiconductor laser based on REC technique is investigated. By mapping the contour lines of the P-I contour diagram of this in-line tunable laser into the wavelength-current contour map, the maximum output power and the tuning curve is obtained. Numerical studies are carried on under linear and quadratic relations, as well as an experiment measurement. Results shows it's a feasible method to find the maximum output power and obtain working currents for the current-controlled in-line semiconductor lasers.

The Design of a Low-Cost Tunable Laser Based on Reconstructed Equivalent Chirp

With the development of optical fiber communication, tunable laser design has become an international research hot spot. In this paper, a new type distributed feedback (DFB) tunable laser is introduced. It uses the Reconstruction-Equivalent-Chirp (REC) technology, combining the stepped chirp sampling structure and superstructure fiber Bragg grating structure. We can obtain continuous tunable multi-channel laser and achieve the purpose of eliminating chirp of the chirp pulse and compressing pulse width at the same time. Through the simulation calculation, it can be known that the output power of each laser’s channel are roughly equal. The laser can realize the tuning between 1530 nm to 1560 nm. And for the initial pulse with the conditions of Tin = 20 ps, the chirp coefficient C = 5 and time-bandwidth product is 2.25, time-bandwidth product will change to 0.458 after REC compression. The compression ratio is about 5:1, which means the pulse frequency chirp can be basically eliminated. The structure only needs to be manufactured by traditional lithography. Its low cost and excellent performance leads to a good applied prospect.

High Precision Dual Frequency Doppler Lidar Based on Monolithic Integrated Two-Section DFB Lasers

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.

Experimental Demonstration of π Equivalent Phase-Shifted SBG Laser With Controlled Distributed Phase Shift

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.

1.3-µm 4×25-Gb/s hybrid integrated TOSA and ROSA

The design and fabrication of a compact and low-cost 4×25-Gb/s transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA) using a hybrid integrated technique are reported. TOSA and ROSA are developed without thermoelectric cooler for coarse wavelength division multiplexing applications. Physical dimension of the packaged optical subassembly is limited to 11.5 mm×5.4 mm×5.4 mm. The design of TOSA and ROSA is employed using a silica-based arrayed waveguide grating chip to select the specific channel wavelength at O-band. In TOSA, the wavelength of four 1.3-µm discrete directly modulated laser chips is well controlled based on the reconstruction equivalent chirp technique. In the back-to-back transmission test, bit error rates for all lanes of cascade of the TOSA and ROSA are small. A clear opening eye diagram is obtained.

Simple frequency-tunable optoelectronic oscillator using integrated multi-section distributed feedback semiconductor laser.

A novel approach to realizing an optoelectronic oscillator (OEO) based on an integrated multi-section (IMS) distributed feedback (DFB) laser is proposed and experimentally demonstrated. Our scheme adopts the method of direct modulation and a built-in microwave photonic filter (MPF), making the structure simpler and more flexible than an external modulator and electrical bandpass filter (EBPF). The IMS-DFB laser, which can overcome the drawbacks of using discrete lasers, is the key device in the scheme. Further, the two DFB sections, which are fabricated by Reconstruction Equivalent Chirp (REC) technique, are injected mutually. The SSB phase noise of the generated signal at the frequency of 20.3 GHz is -115.3 dBc/Hz@10kHz and -92.9 dBc/Hz@1kHz. The sidemode suppression ratio (SMSR) is 60.94 dB, which is a 40 dB improvement over a single loop. Furthermore, we demonstrate that the phase noise improves about 8 dB at the frequency offset of 1 kHz, when employing 13 km and 5.4 km fibers as the dual loop. The simple and compact structure, which consists of an IMS-DFB laser with high wavelength controlling accuracy and low process requirement, is a promising development for OEO integration.

Photonic generation of linearly chirped microwave waveforms using a monolithic integrated three-section laser.

Photonic generation of linearly chirped microwave waveforms (LCMWs) using a monolithic integrated three-section laser is experimentally demonstrated in this work. All three sections of the laser cavity, including the front DFB section, phase section and rear DFB section, have the same active layer, which can avoid the butt-joint re-growth process. The gratings in both DFB sections are fabricated by the Reconstruction Equivalent Chirp technique, which can significantly decrease the difficulties in realizing precise grating structure. By adjusting the integrated three-section semiconductor laser to work in the period-one (P1) state and applying a sweeping signal to the front DFB section, the beating signal, i.e., an LCMW with a large time bandwidth product (TBWP), can be generated. In the current proof-of-concept experiment, an LCMW with a large TBWP up to 5.159 × 105 is generated, of which the bandwidth and the duration time are 6.7 GHz and 77 us respectively. The compressed pulse width is 150 ps. In addition, by adjusting the bias currents of the rear DFB section and front DFB section as well as the amplitude of the sweeping signals, LCMWs with tunable center frequency and tunable bandwidth can be achieved.