Lasing characteristics for four-section MQW-DBR laser

A MQW-DBR laser with two active sections and low tuning efficiency has been developed. The device showed excellent lasing characteristics: a low threshold current of 10 mA, a high slope efficiency of 0.26 mW/mA, and a narrow linewidth of 280 kHz at P_out=15 mW. A red-shift carrier-induced FM response was obtained by nonuniform current injection to two active sections. A flat FM response with wide bandwidth (>2 GHz) was confirmed. The linewidth broadening due to wavelength tuning was suppressed through the reduction of tuning efficiency. A continuous tuning range of 0.8 nm was observed while maintaining the linewidth below 4 MHz     

A theoretical model of multielectrode DBR lasers

A theoretical model for two- and three-section tunable distributed Bragg reflector (DBR) lasers is presented. The static tuning properties are studied in terms of threshold current, linewidth, oscillation frequency, and output power. Regions of continuous tuning for three-section DBR lasers are presented. Different routes for continuous tuning, when the injection currents to the passive sections are varied, are discussed and the limitations on the continuous tuning range are clarified. By proper control of these currents, a tuning range of approximately 400 GHz is predicted at 1.55 μm wavelength, which is in good agreement with the experimental results published thus far     

Frequency noise and modulation of a four-section DBR laser

A theoretical model is presented to describe the tuning, frequency noise, and modulation characteristics of tunable DBR lasers with two active and two passive sections. Analytical expressions are derived for the intensity and frequency modulation responses, frequency noise spectrum, spectral linewidth, effective linewidth enhancement factor, and spontaneous emission rate. It is shown that a nearly flat red-shifted FM response over several gigahertz can be obtained by nonuniform current injection and modulation of the lower carrier density section in the active region. Increasing the tuning current through the passive sections enhances the FM efficiency. However, a higher FM efficiency is generally accompanied by a larger spectral linewidth. The predictions of our theoretical model are in good agreement with the available experimental data     

A DBR laser employing passive-section heaters, with 10.8 nm tuningrange and 1.6 MHz linewidth

A wavelength-tunable, three-section, distributed Bragg reflector (DBR) InGaAsP/InP laser diode is described. The refractive indices of the DBR section and the phase-control section are thermally controlled by thin-film heaters embedded on these passive sections. This structure enables wide-range wavelength tuning without the spectral linewidth broadening accompanying conventional tuning by current injection into the passive sections. A tuning range of 10.8 nm and a linewidth of less than 1.6 MHz have been achieved in the 1.5-μm wavelength region. The temperature increase in the active layer is held to within a few degrees, even when the DBR-section temperature reaches 90°C     

A theoretical analysis of linewidth broadening in frequency tunableDBR lasers

Linewidth broadening in frequency tunable distributed-Bragg-reflector (DBR) lasers with tuning sections is analyzed. The analysis is based on a simplified two-section single-mode cavity model and quantum mechanical Langevin treatment. The origin of linewidth broadening is shown to be low frequency excess FM noise caused by carrier fluctuation in the tuning section. A scaling law, which permits optimal device parameter design, is then derived. When a decrease in the carrier lifetime is combined with an increase in the tuning current, linewidth broadening can be suppressed without frequency tuning range reduction     

Dispersive self-Q-switching in self-pulsating DFB lasers

Self-pulsations reproducibly achieved in newly developed lasers with two distributed feedback sections and with an additional phase tuning section are investigated. The existence of the dispersive self-Q-switching mechanism for generating the high-frequency self-pulsations is verified experimentally for the first time. This effect is clearly distinguished from other possible self-pulsation mechanisms by detecting the single-mode type of the self-pulsation and the operation of one section near the transparency current density using it as a reflector with dispersive feedback. The operating conditions for generating this self-pulsation type are analyzed. It is revealed that the required critical detuning of the Bragg wavelengths of the two DFB sections is achieved by a combination of electronic wavelength tuning and current-induced heating. The previous reproducibility problems of self-pulsations in two-section DFB lasers operated at, in principle, suited current conditions are discussed, and the essential role of an electrical phase-control section for achieving reproducible device properties is pointed out. Furthermore, it is demonstrated that phase tuning can be used for extending the self-pulsation regime and for optimizing the frequency stability of the self-pulsation. Improved performance of the devices applied as optical clocks thus can be expected     

Digital tuning of high-order high-Q continuous-time filters

A digital tuning scheme for automatic tuning of high-order high-Q continuous-time filters is proposed. The scheme uses phase information for both centre frequency and Q tuning, and does not rely on the relation between the passband gain and Q factor. Digital control of frequency and Q tuning loops improves the stability by enabling only one loop at a given tuning cycle. High-order filter tuning is performed without separating individual sections, eliminating switches and their parasitics     

Widely tunable 850-nm metal-filled asymmetric cladding distributed Bragg reflector lasers

Broadly tunable distributed Bragg reflector (DBR) lasers utilizing metal-filled surface-etched diffraction gratings were fabricated on a GaAs-unstrained quantum well with AlGaAs core and cladding layers. Devices with 200- and 400-/spl mu/m gratings sections were fabricated. Single-mode devices are fabricated over a broad spectral range, exhibiting over 55 mW of single-facet output power. The optical properties of this structure are analyzed in terms of effective index step between the peak and valley of the grating and scattering loss in the DBR. Discrete devices were fabricated with lasing wavelengths between 846.6 and 862.9 nm at intervals of 1.44nm, representing a range of 16.3 nm. Wavelength tuning by current injection into the DBR section is explored, and a broad tuning range of over 18 nm is measured while single-mode performance is maintained. The spectral linewidth of these devices is measured. The temperature dependence of light versus current, threshold current values, and spectral characteristics are also examined.     

Design and analysis of widely tunable sampled grating DFB laser diode integrated with sampled grating distributed Bragg reflector

A new widely tunable laser diode structure that requires only two tuning currents is proposed. The laser diode consists of a sampled grating distributed feedback (SGDFB) laser diode monolithically integrated with a sampled grating distributed Bragg reflector (SGDBR). The phase control sections are properly inserted between the grating bursts of the SGDBR and SGDFB sections for the discrete and continuous tuning. To confirm the feasibility of the new structure, the split-step time domain model is used. The simulation result for a particular design shows that the tuning range as wide as 27 nm is possible with side-mode suppression ratio exceeding 35 dB. Furthermore, the output power is larger than that from SGDBR laser diodes with similar parameters.     

Tunability limitations of microwave resonators tuned by several capacitances and inductances

Tunability limitations of resonators that consist of transmission line sections and are tuned by several capacitances and inductances are established. The limitations are common for lossy and lossless resonators. It is shown that an increase in the number of tuning elements does not lead to increasing frequency ratio. It is proved that combined tuning is more effective that tuning by one-type elements. This tuning makes possible continuous variation of the resonance frequency in a wide range exceeding a decade.     

准连续调谐35nm的SGDBR激光器的研制

对接生长技术可以独立优化不同区域的波导结构,有利于制作高性能的半导体光电子集成器件.文中采用MOCVD对接生长技术制作了SGDBR激光器,通过载流子注入,器件准连续调谐范围为35nm,在调谐范围内边模抑制比大于30dB.     

准连续调谐35nm的SGDBR激光器的研制

对接生长技术可以独立优化不同区域的波导结构,有利于制作高性能的半导体光电子集成器件. 文中采用MOCVD对接生长技术制作了SGDBR激光器,通过载流子注入,器件准连续调谐范围为35nm,在调谐范围内边模抑制比大于30dB.     

Frequency and wavelength tunable optical microwave source based on a distributed Bragg reflector self-pulsation laser

A frequency and wavelength tunable self-pulsation laser based on DBR laser devices is reported for the first time.This laser generates continuous tunable optical microwave in the range of 1.87-21.81 GHz with 3-dB linewidth about 10 MHz by tuning the injection currents on the front and back gain sections,and exhibits wavelength tuning range from 1536.28 to 1538.73 nm by tuning the injection currents on the grating section.     

Rigorous analysis of novel dielectric resonator filters with printed tuning septum

This paper describes the analysis of dielectric resonator filters with printed tuning septum in waveguide sections operating below cutoff. In this design approach a thick dielectric slab of high permittivity is placed longitudinally in the waveguide. A bilateral ladder-shaped metallization determines the resonator and coupling sections (modified finline filter). In contrast to conventional dielectric resonator filters, this approach provides better passband separation and increased stopband attenuation. Furthermore, due to the bilateral tuning septum, the resonator and coupling sections can be manufactured accurately with photolithographic techniques rather than by expensive machining.     

Wavelength tuning mechanism in three-electrode DFB lasers

The wavelength tuning mechanism is investigated for three-electrode distributed feedback (DFB) InGaAs-InGaAsP lasers. It is shown that the side and center sections play different roles in wavelength tuning: the former determines the effective Bragg wavelength and the latter contributes through the round-trip phase condition. The lasing wavelength is expressed in a simple form that renders the wavelength shift behavior exceedingly understandable. The indispensability of the thermal contribution to continuous broad range tuning is also clarified both theoretically and experimentally     

A digital automatic tuning technique for high-order continuous-time filters

A digital automatic tuning technique for high-order continuous-time filters is proposed. Direct tuning of overall response is achieved without separating individual biquad sections, eliminating switches and their parasitics. Output phase of each biquad section is tuned to known references, which are generated by a frequency synthesizer. The core tuning circuit consists of D flip-flops (DFF) and simple logic gates. DFFs are utilized to perform binary phase detection. Frequency and quality factor tuning loops for each biquad are controlled digitally, providing more stable tuning by activating only one loop at a given time. The tuning system was verified by a prototype sixth-order bandpass filter which was fabricated in a conventional 0.5 /spl mu/m CMOS process with /spl plusmn/1.5 V power supply.     

InGaAs-GaAs脊波导DBR激光器双模运行特性研究

对一种新型InGaAs-GaAs脊波导分布式Bragg反射(DBR)半导体激光器双模运行特性进行了研究.该激光器由1个普通增益区和2个DBR区组成,两DBR区采用均匀蚀刻的Bragg光栅,中间加入50～100 μm的分隔区,以减小两DBR区间的热作用影响.实验发现,在增益区偏置电流强度满足双模(双波长)运行条件的情况下,在分隔区施加一电流Ispace,会对双模调谐特性产生非常大的影响.结果表明:施加适当的Ispace可使双波长的可调谐间隔显著增加,并同时提高2个激射模的边模抑制比;在一定的范围内,较大的Ispace对应较好的双模运行参数.测量了3种几何尺寸样品在多种偏置电流下的双模运行特性,对分隔区长度、Ispace以及两者组合对双模调谐特性的影响作了深入研究.研究结果对改善双波长DBR半导体激光器双模运行特性给出了有用的信息.     

A fully integratable 1.55-/spl mu/m wavelength continuously tunable asymmetric twin-waveguide distributed Bragg reflector laser

We demonstrate a single-frequency continuously tunable three-section distributed Bragg reflector laser operating at a center wavelength of /spl lambda//sub 0/=1.548 /spl mu/m using a fully integratable asymmetric twin-waveguide structure. A low-loss tapered mode transformer couples the light between the active waveguide, or gain region, and the passive ridge waveguide where the phase and grating tuning sections are located. The device has a threshold current of 50 mA and output power of nearly 13 mW, with a slope efficiency of 0.12 W/A and a tuning range of 4.8 nm under pulsed operation. An independent phase section is used to continuously tune the wavelength, thus avoiding mode hops. Using a delayed self-heterodyne technique, we determine the linewidth to be (146/spl plusmn/2) kHz.     

应用增益杠杆效应提高分布反馈激光器的波长可调谐范围

在三段电注入应变多量子阱分布反馈激光器中，应用增益杠杆效应扩大了波长的可调谐范围。对其中两段加固定偏置直流电流，另一段作为控制段（其长度为总腔长的０．３３）。随着对控制段注入电流的增加，发射波长会往长波方向移动。其波长连续可调谐范围（不含跳模）在１．５３８μｍ波段可达０．８２ｎｍ。经过跳模后尚可连续调谐。     

Wavelength-independent output power from an injection-tunable DBRlaser

Injection-tunable three-section distributed Bragg reflector lasers emitting near 1.55 μm have been fabricated employing bulk 1.48-μm-bandgap InGaAsP in the tuning layer of the phase and Bragg sections. The gain in this material compensates for the increased absorption loss during tuning, which results in a nearly wavelength-independent optical output power. The maximum obtained output power is 28 mW ex facet, with a spectral linewidth around 5 MHz