DFB Section Research Articles

A Novel High Speed Directly Modulated Dual Wavelength 1.3 μm DFB Laser for THz Communications

We report a novel high speed directly modulated dual wavelength 1.3 μm laser for THz communication applications. The laser has a compact size and simple structure, which consists a DFB section and a passive distributed Bragg reflector (DBR) section, leading to a device fabrication procedure similar to that of a normal DFB laser. The laser has an over 26 GHz modulation bandwidth in the dual wavelength working mode, which facilitates high speed data modulation onto THz wave. NRZ data modulations at up to 50 Gb/s have been demonstrated successfully. The bit error rate (BER) performances under 10 and 25 Gb/s NRZ data modulation are studied. 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> BER can be obtained and the 10 km fiber transmission power penalty when compared with the back to back transmissions is less than 0.5 dB. This device is a low-cost but powerful light source for future photonics based high speed THz communication system.

A Monolithically Integrated Two-Section Laser for Wideband and Frequency-Tunable Photonic Microwave Generation

A monolithically integrated two-section laser is presented for wideband and frequency-tunable photonic microwave generation. The laser consists of two back-to-back DFB sections forming a mutually coupled structure. By properly adjusting the bias currents of two sections, the laser can stably work at the state of period-one oscillation over a wide range of frequency detuning. Based on this, continuous and linear tuning of photonic microwave signals can be achieved. Experimental results confirm that a large tunable range from 12.45 to 80.30 GHz can be realized using this laser.

50 Gb/s Electro-Absorption Modulator Integrated with a Distributed Feedback Laser for Passive Optical Network Systems

We report an electro-absorption modulator integrated with a distributed feedback Bragg laser fabricated by butt-joint technology. The lasing wavelength of the EML laser was 1311.71 nm, the output power was 10.04 mW when the current of the DFB section was 100 mA, the side-mode suppression ratio was greater than 50 dB, and the small-signal bandwidth was 29.40 GHz when the bias voltage of the modulator was −2 V. A 50 Gb/s data transmission over a single-mode fiber of up to 10 km was realized, which could be used as a light source for 50 G passive optical network systems.

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.

Experimental Demonstration of Amplified Feedback DFB Laser With Modulation Bandwidth Enhancement Based on the Reconstruction Equivalent Chirp Technique

A novel amplified feedback DFB laser with extended modulation bandwidth is experimentally demonstrated in this paper. All the three sections of laser cavity, including DFB section, phase section, and amplified feedback section, have the same active layer, which can avoid the butt-joint regrowth process. The gratings in both DFB section and amplified feedback section are fabricated by the reconstruction equivalent chirp technique, which can significantly decrease the difficulties in realizing precise grating structure. An enhanced −3 dB bandwidth of 19 GHz is achieved by means of a normal low-frequency wafer. Modulation linearity and relative intensity noise characteristics are experimentally investigated. 20 MSymbol/s 32-QAM signal with 19 GHz carrier is transmitted via 25-km radio-over-fiber link using the as-fabricated directly modulated DFB laser, and the average error vector magnitude of the whole link is 3.91%.

Electro-absorption Modulated Lasers with High Immunity to Residual Facet Reflection by Using Lasers with Partially Corrugated Gratings

Residual facet reflection can significantly degrade the performance of electroabsorption modulated lasers (EMLs) operating at high data rates. This issue also complicates the fabrication and characterization of the highly demanded light sources for optical interconnects and transmission. It is desired to optimize the device structure to make EMLs robust and immune to residual facet reflection. EMLs with a partially corrugated-grating DFB section are designed and optimized to have much improved tolerance to the residual optical reflection from the modulator output facet. By designing the laser section with an appropriate grating length and linear gain coefficient, the EML can have good tolerance to residual facet reflection. The analysis indicates that 100% yield can be obtained with the optimal design. If the EML needs to operate over a wide ranges of gain coefficient and facet reflection, >70% of yield can still be obtained.

Wide bandwidth chaotic signal generation in a monolithically integrated semiconductor laser via optical injection

Abstract Wide bandwidth chaotic signal generation in a three-section monolithically integrated semiconductor laser (MISL) under external optical injection is investigated experimentally. Through evaluating the effective bandwidth of chaotic signals, the influences of the optical injection on the bandwidth of chaotic signal from the MISL are analyzed. The experimental results indicate that, for the currents of the DFB section (IDFB) and the phase section (IP) are fixed at 70.00 mA and 34.00 mA, respectively, the effective bandwidth of chaos signal generated by the solitary MISL reaches its maximum value of 14.36 GHz when the current of the amplification section (IA) takes 23.22 mA. After an external optical injection is introduced into the MISL, the effective bandwidth of the generated chaotic signal can be beyond 2.5 times of the maximum value. Furthermore, the effects of the injection strength and the frequency detuning on the effective bandwidth of the generated chaotic signal are also discussed.

Laterally coupled dual-grating distributed feedback lasers for generating mode-beat terahertz signals.

We present a laterally coupled dual wavelength 1.56/1.57-μm AlGaInAs/InP DFB laser, which, by introducing two different grating periods on each sidewall, emits two longitudinal modes simultaneously within the same cavity at a frequency separation of 0.82THz. The beating signal is stabilized by nonlinear four-wave mixing in an electro-absorption modulator (EAM), located within a monolithically integrated resonant cavity. A stable 0.82-THz beating signal was observed over a wide range of bias parameters in terms of drive currents and bias to the DFB and EAM sections.

Direct generation of broadband chaos by a monolithic integrated semiconductor laser chip

A solitary monolithic integrated semiconductor laser (MISL) chip with a size of 780 micrometer is designed and fabricated for broadband chaos generation. Such a MISL chip consists of a DFB section, a phase section and an amplification section. Test results indicate that under suitable operation conditions, this laser chip can be driven into broadband chaos. The generated chaos covers an RF frequency range, limited by our measurement device, of 26.5GHz, and possesses significant dimension and complexity. Moreover, the routes into and out of chaos are also characterized through extracting variety dynamical states of temporal waveforms, phase portraits, RF spectra and statistical indicators.

Tunable dual-mode DFB laser for millimetre-wave signal generation

Highly compact dual-mode semiconductor laser sources get more and more attention in different application fields such as radar, security and personal communication systems. When the two generated wavelengths are detected within the same photodetector, an electrical signal which frequency is the difference between the frequencies of the two optical modes will be issued. We report on an integrated semiconductor device which is composed of two in-line DFB sections that are using the same optical waveguide structure. The so generated dual-mode spectrum can be adjusted first, by the difference in the grating parameters of each DFB section and second, by their respective driving current. We will report on the characterisation of such a device focusing on tunability and linewidth aspects that are of prime importance in above mentioned applications.

Dynamics of symmetrical mode beating in complex coupling two-section DFB lasers

The effect of gain/loss coupling on the modal dynamics of weakly-coupled self-pulsating two section DFB lasers is studied in detail. A purely symmetrical mode-beating regime exists for imaginary coupling values between − 5% and 12.5%. The minimum required static detuning, the modulation index, and the tuning range of the predicted self-pulsations are sensitive to the magnitude of the gain/loss coupling. For the 10% gain-coupled DFB laser above 90% modulation index is predicted for self-pulsations between 34% and 123 GHz. For the 5% loss-coupled DFB laser above 50% modulation index is predicted for self-pulsations between 27 and 155 GHz.

양 단면 반사율과 위상 조정 영역의 위상이 다중 영역 Complex-Coupled DFB 레이저의 수율 특성에 미치는 영향

양 단면 반사율과 단면 회절격자의 위상, 위상 조정 영역의 위상이 두 개의 DFB 영역과, 가운데 위상 조정 영역을 가진 다중 영역 CC(complex-coupled) DFB 레이저의 SP(self-pulsation) 동작 특성에 미치는 영향을 수율 관점에서 살펴보았다. 결합세기와 CR(coupling ratio)이 작을수록 양 단면과 다른 DFB 영역에서 반사되는 필드가 모드의 특성에 미치는 영향이 증가하여 수율이 감소한다. 결합세기와 CR에 상관없이 양 단면 반사율이 증가할수록 최대 수율과 수율이 60% 이상 되는 위상 조정 영역의 위상 범위가 감소함을 볼 수 있었다. 같은 결합세기에서는 CR이 0.2인 경우가 CR이 0.1인 경우보다 복소 결합 효과가 커 최대 수율과 수율이 60%이상 되는 위상 조정 영역의 위상 범위가 큼을 볼 수 있었다. 결합세기가 3이고 CR이 0.2인 경우가 DFB 영역의 발진 모드가 외부의 영향을 적게 받고 SHB(spatial hole burning) 효과도 크지 않아 양 단면 반사율의 변화와 위상 조정 영역의 위상 변화에 따른 수율 특성이 가장 좋음을 볼 수 있었다. The effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection complex-coupled (CC) DFB lasers is investigated in terms of yield. The lasers are composed of two CC DFB sections and a phase tuning section between them. As the coupling strength and the coupling ratio (CR) decrease, the effect of the reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases, so that the yield decreases. As the facet reflectivity increases, the maximum yield and the range of the phase of a phase tuning section with yield more than 60% decrease independent of the coupling strength and CR. The yield characteristics of CR=0.2 are better than those of CR=0.1 with the same coupling strength due to the larger complex coupling effect. The case with <TEX>${\mid}{\kappa}L{\mid}=3$</TEX> and CR=0.2 shows best yield characteristics among the cases considered in this work.

이득 분산이 다중 영역 복소 결합 DFB 레이저의 Self-Pulsation 특성에 미치는 효과

이득 분산이 두 개의 복소 결합 DFB 영역과 위상조정 영역으로 구성되는 다중 영역 복소 결합 DFB 레이저에서 발진하는 두 모드의 비팅에 의한 self-pulsation (SP) 주파수와 출력 파워의 변조지수에 미치는 영향에 대하여 살펴보았다. 능동 영역의 이득이 최대가 되는 파장을 두 DFB 영역의 발진 모드의 파장 중심 또는 브래그 파장 중심에 위치시킨 경우가 특정 DFB 영역의 발진 모드의 파장 또는 브래그 파장에 위치시킨 경우에 비하여 두 DFB 영역의 브래그 파장 차이, <TEX>${\Dalta}{\lambda}_{B}$</TEX>, 증가에 따른 두 발진 모드가 받는 이득 차이가 적게 발생하여 최대 SP 주파수가 크고, 변조지수 특성도 좋음을 볼 수 있었다. 또한 능동 영역의 이득이 최대가 되는 파장을 두 DFB 영역의 브래그 파장 중심에 위치시키는 경우가 발진 모드의 파장 중심에 위치시키는 경우에 비하여 더 큰 최대 SP 주파수를 얻을 수 있었고 변조지수 특성도 더 우수함을 볼 수 있었다. The effect of gain dispersion on the self-pulsation (SP) characteristics due to the mode beating of two modes emitted in a multisection DFB laser composed of two complex-coupled DFB sections and a phase control section is investigated. When the peak wavelength, <TEX>${\lambda}_{p}$</TEX>, of the gain spectrum of the DFB section is positioned in the center of the lasing wavelengths or the Bragg wavelengths of the two DFB sections, the maximum SP frequencies are higher and the modulation index has better characteristics compared to those cases for <TEX>${\lambda}_{p}$</TEX> fixed at the lasing wavelength or Bragg wavelength of one DFB section, when the difference between the Bragg wavelengths of the two DFB sections, <TEX>${\Dalta}{\lambda}_{B}$</TEX>, is varied. When <TEX>${\lambda}_{p}$</TEX> is positioned in the renter of the Bragg wavelengths of the two DFB sections, the maximum SP frequency is higher and of the modulation index has better characteristics compared to those of the case for <TEX>${\lambda}_{p}$</TEX> positioned in the center of the lasing wavelengths of the two DFB sections.

Measurement of small-signal and large-signal responses of packaged laser modules at high temperature

In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules, such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved at higher temperature.

양 단면 반사율과 위상 조정 영역의 위상이 다중 영역 Index-Coupled DFB 레이저의 수율 특성에 미치는 영향

양 단면 반사율과 단면 회절격자 위상, 위상 조정 영역의 위상이 두 개의 DFB 영역과, 가운데 위상 조정 영역을 가진 다중 영역 Index-Coupled DFB 레이저의 Self-Pulsation동작 특성에 미치는 영향을 수율 관점에서 살펴보았다. 결합세기가 작을수록 양 단면 반사율이 증가할 때 양 단면과 다른 DFB 영역에서 반사되는 필드가 모드의 특성에 미치는 영향이 커져 양 단면 회절격자 위상 변화에 따른 발진 모드의 호핑이 많이 발생하고 수율이 감소한다. 결합세기가 클수록 양 단면 반사율이 증가하여도 양 단면과 다른 DFB 영역에서 반사되는 필드가 모드의 특성에 미치는 영향이 작아 양 단면 회절격자 위상 변화에 따른 모드의 호핑은 적게 발생하나 Spatial Hole Burning 효과가 증가하여 수율이 감소하는 것을 볼 수 있었다. 결합세기에 상관없이 단면 반사율이 증가할수록 최대 수율과 수율이 40% 이상 되는 위상 조정 영역의 위상 범위가 감소함을 볼 수 있었다. 또한 결합세기가 클수록 위상 조정 영역의 위상 변화에 따른 수율의 변화가 커지고 단면 반사율의 변화에 따른 최대 수율을 주는 위상 조정 영역의 위상 값의 변화가 작음을 볼 수 있었다. 결합세기가 2와 3일 경우가 1.2와 4인 경우에 비하여 수율 특성이 좋음을 볼 수 있었다. We investigate the effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection index-coupled (IC) DFB lasers composed of two index-coupled DFB sections and a phase tuning section between them in terms of yield. In the case of weak coupling strength, as the reflectivity of both facets increases, the effect of reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases. Thus the number of mode hoping increases and yield decreases for the variation of phases of both facets. In the case of strong coupling strength, as the reflectivity of both facets increases, the spatial hole burning effect increases, so that the yield decreases. The maximum yield and the range of the phase of a phase tuning section with yield more than 40% decrease as the facet reflectivity increases irrespective of coupling strength. As the coupling strength increases, the variation of yield for the variation of the phase of a phase tuning section increases and the variation of the phase of a phase tuning section with the maximum yield for the variation of the reflectivity of both facets decreases. The yield characteristics of the cases with the coupling strengths of 2 and 3 are better than those with the coupling strengths of 1.2 and 4.

매우 넓은 영역의 Self-Pulsation 주파수와 높은 변조 지수를 가자는 다중 영역 복소 결합 DFB 레이저

We analyze the self-pulsation(SP) characteristics due to mode beating of two modes emitted in a multi-section complex-coupled (CC) DFB laser composed of two DFB sections and a phase control section between them. SP frequency due to mode beating of the two modes is determined by the difference of grating periods in the two CC DFB regions. As the difference of grating periods in the two CC DFB regions increases, the SP frequency increases from very low frequency to the THz region. In the case of a mode which is not located in the stop band of the other DFB region, the mode propagates into the other DFB region without a high reflection, so that output powers emitted in a multi-section CC DFB laser have high modulation indexes due to the large interaction between the two modes.

증폭된 광 귀환을 가자는 다중 전극 복소 결합 DFB 레이저에서 발생되는 self-pulsation 특성 해석

하나의 DFB 영역, 위상 조정 영역과 이득 영역으로 구성된 다중 전극 DFB 레이저의 pulsation 동작 특성을 살펴본다. Anti-phase (AP) complex-coupled (CC) DFB 구조를 사용한 경우가 in-phase CC DFB 구조나 index-coupled DFB 구조를 사용한 경우에 비하여 안정된 pulsation 동작이 발생하는 이득 영역과 위상 조정 영역의 전류 범위가 큼을 알 수 있다. AP CC DFB 구조를 사용한 경우 결합 세기가 커질수록, 이득 결합 계수가 커질수록 안정된 pulsation 동작이 발생하는 이득 영역의 전류 범위가 증가하고 pulsation 주파수의 튜닝 영역이 커짐을 볼 수 있다. 또한 위상 조정 영역의 위상 변화에 의한 pulsation주파수의 튜닝 영역도 커짐을 볼 수 있다. 고정된 결합 세기에서 DFB 영역의 길이가 증가할수록 pulsation 동작이 발생하는 위상 조정 영역과 이득 영역의 전류 범위가 증가하여 pulsation 주파수 튜닝 영역이 넓어짐을 볼 수 있다. We investigate the pulsation characteristics in a multi-section DFB laser which is composed of one DFB section, phase tuning section, and gain section. Multi-section DFB lasers with anti-phase (AP) complex-coupled (CC) DFB structure show wide current ranges of gain and phase tuning sections fer stable pulsations compared to those with in-phase CC DFB structure or index-coupled DFB structure. For multi-section DFB lasers with AP CC DFB structure, the current range of a gain section for stable pulsations increases and the tuning range of the pulsation frequency increases as a coupling strength or a gain coupling coefficient increases Also, the tuning range using the phase variation in a phase tuning section increases. For a fixed coupling strength, the current ranges of gain and phase tuning sections for stable pulsations increase and the tuning range of the pulsation frequency increases as the length of a DFB section increases.

다중 전극 Index-Coupled DFB 레이저에서 결합 세기 및 각 영역의 길이가 Self-Pulsation 동작 특성에 미치는 영향

As the number of compound cavity modes within the stopband of DFB sections decreases, the frequency of mode hopping decreases for the variation of λ, which represents the difference between the Bragg wavelengths of two DFB sections, so that the number of abrupt changes of pulsation frequencies decreases. In addition, the pulsation frequency varies continuously for the variation of the phase in a phase tuning section for a fixed λ. The number of compound cavity modes within the stopband decreases as the length of DFB sections increases and the length of a phase tuning section decreases. Thus stable self-pulsation operations for the variation of λ and the phase in a phase tuning section could be obtained by proper selection of the coupling strength and the length of each section.ction.

Analysis of surface-emitting second-order distributed feedback lasers with central grating phaseshift

An analysis of second-order distributed feedback lasers (DFB) with central grating phaseshift is performed. The devices have an active grating (i.e., DFB) section, passive grating sections (i.e., DBRs); and the active grating is formed at a metal-semiconductor interface. Coupled-mode theory and the transfer matrix method are employed. It is found that a central grating phaseshift, /spl Delta//spl phi/, of 180/spl deg/ causes the laser to radiate in a beam of symmetric near-field amplitude profile, in sharp contrast to conventional second-order DFB lasers which radiate in beams of asymmetric near-field amplitude profile. In turn the far-field profile becomes a single-lobe beam pattern. Thus, a means to fundamentally obtain surface emission in an orthonormal single-lobe beam from a second-order DFB/DBR device has been found. The orthornomal-beam emission is achieved at no penalty in device efficiency. External differential quantum efficiencies, /spl eta//sub d/, in excess of 70% can be obtained, and the guided-field intensity profile is substantially uniform. The effects of the lengths of the DFB section (L/sub DFB/) and of each of the DBR sections (L/sub DBR/) on device performance are analyzed and optimal values are found to occur for L/sub DFB/ in the 500-700 /spl mu/m range and for L/sub DBR/ in the 600-700 /spl mu/m range. One can obtain /spl eta//sub D/ values as high as 76% from devices with 80% of the energy in the central lobe, and moderate threshold gains (i.e., 40 cm/sup -1/). Threshold gains as low as 25 cm/sup -1/ can also be obtained from highly efficient devices (i.e., /spl eta//sub D//spl cong/70%), at some penalty in guided-field uniformity. In either case the intermodal discrimination is quite high (70-75 cm/sup -1/). Gratings with half-wave (i.e., /spl pi/) phaseshifts have been fabricated by using the dual-tone photoresist method, and the concept has been experimentally proven: orthonormal, single-lobe emission in a diffraction-limited beam from 1500 /spl mu/m-long devices. Extension to two-dimensional (2-D) large-aperture: 200 /spl mu/m/spl times/1500 /spl mu/m; surface emitters is quite possible, which should allow for the emission of watts of coherent CW power in a stable, single mode. The 2-D structure represents a defect-free, second-order active photonic lattice.

Self-Pulsation in Multisection Distributed Feedback Laser Diode with a Novel Dual Grating Structure

A self-pulsating multisection distributed-feedback laser diode (DFB LD) can potentially realize all-optical clock extraction. This device generally consists of three sections, two DFB sections and one waveguide section. The most important variable in this device is detuning, which is the relative spectral position between the stop bands of two DFB sections. We fabricated a novel structure in which two gratings were located one over and one under the active layers. Each grating structure was independently defined in processing so that detuning, which is the prerequisite for self-pulsation, could be easily controlled. Observing various self-pulsating phenomena in these devices under several detuning conditions, we characterized the phenomena as dispersive Q-switching, mode beating, and self-mode-locking.