Gain-coupled DFB Lasers Research Articles

Improved performance of complex gain-coupled DFB laser by using tapered grating structure

In this paper, theoretical analysis of antireflection complex gain coupled distributed feedback lasers (CGC-DFB) with tapered grating structure has been presented. Two types of gratings, convex and concave tapered grating with longitudinal variable depth, in active layer have been proposed. Evaluation of flatness parameter variation above threshold condition shows that concave tapered grating improves the stability of CGC-DFB laser against spatial hole burning (SHB) effect. The dependencies of output power, side mode suppression ratio (SMSR) and oscillation wavelength of CGC-DFB laser on convex and concave grating parameters have been studied. Both convex and concave tapered grating CGC-DFB structures have higher output power than conventional CGC-DFB lasers with uniform grating. It is found that, concave tapered grating structure with parameters p0 = 15 nm and a0 = 0.7 nm has minimum flatness parameter, stable lasing wavelength and flat SMSR profile as a function of current. Theoretical calculation model is based on the numerical solution of coupled wave equations and carrier rate equation by using transfer matrix method. In numerical calculation SHB effect has been assumed.

A Standing-Wave Model Based on Threshold Hot-Cavity Modes for Simulation of Gain-Coupled DFB Lasers

A time-domain standing-wave model is proposed and developed to analyze the gain-coupled DFB laser. In this model, the optical field is decomposed into a set of eigenmodes, which are longitudinal cavity modes obtained when the laser is biased near threshold, i.e., threshold "hot-"cavity modes. As such, the spatial and temporal dependence of the optical field is separated with optical modes describing the spatial dependence and their amplitudes governing the temporal evolution of the field. Important effects such as the variation of the coupling coefficient with the injection level and the spatial hole burning can all be taken into account.

Experimental Study of Pattern-Independent Phase Noise Accumulation in an All-Optical Clock Recovery Chain Based on Two-Section Gain-Coupled DFB Lasers

The pattern-independent phase noise accumulation in a chain of all-optical clock recovery devices (CRDs) based on two-section gain-coupled distributed feedback (TS-DFB) laser operating in the coherent mode is studied experimentally and theoretically. A simple theoretical model, where the CRD output phase noise is equal to the sum of the phase noise introduced by the CRD and the CRD input phase noise filtered by the phase noise transfer function, has been proposed for the CRD equivalent phase noise model. The accumulation of pattern-independent phase noise is investigated experimentally and theoretically for different cut-off frequencies of the phase noise transfer function of the TS-DFB laser and two different optical signal to noise ratios. It is shown that, due to the phase noise added by the CRD, phase noise accumulates in the passband of the phase noise transfer function, with the phase noise transfer function well approximated by a first-order lowpass filter. Excellent qualitative agreement between the experimental results and the theoretical model is observed. Also, it is concluded that the phase noise accumulation model for CRD, where the recovered clock is locked to the optical power of the incoming clock signal, presented by other authors holds in a qualitative point of view for the TS-DFB laser operating in the coherent mode. Since the root-mean-square (rms) of the timing jitter is proportional to the square root of the integrated power spectral density of the phase noise, the results show that a smaller cut-off frequency of the phase noise transfer function does not lead to a smaller rms value of the pattern-independent timing jitter along the chain of all-optical CRDs based on TS-DFB laser. It is shown that the minimum rms of the pattern-independent timing jitter along the CRD chain results from a compromise between the cut-off frequency of the phase noise transfer function and the phase noise introduced by the TS-DFB laser.

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.

Injection locked multi-section gain-coupled dual mode DFB laser for terahertz generation

A dual mode multi-section gain-coupled distributed feedback laser with tunable mode spacing is subharmonically injection locked at 0.315 THz. The injected signal consists of an optical comb with harmonics 35 GHz apart and a bandwidth of approximately 1.9 THz. The optical comb is a result of strong four-wave mixing in a highly-nonlinear dispersion-shifted fiber. In order to observe locking of the multi-section laser, the output is optically downconverted to RF frequencies using the same optical comb. The locked multi-section DFB laser is a coherent and tunable optical source suitable for continuous-wave terahertz generation systems.

Comparison of quasi-symmetrical and asymmetrical mode beatings in two-section partially gain-coupled DFB lasers

The self-consistent mode-beating model is applied to a two-section partially gain-coupled distributed feedback (TS-GC DFB) laser with low coupling strengths. The model is based on introducing a fixed detuning parameter to the governing rate equations of the slowly-varying fields. The existence of quasi-symmetrical, a mix of quasi–symmetrical and asymmetrical, and asymmetrical mode beating depends on the coupling strength of the cavity. The quasi-symmetrical mode beating predicted here is similar in characteristics to the mode beating found in index-coupled self-pulsating lasers. It has a continuous and a wide tuning range. The asymmetrical mode beating is capable of producing self-pulsations over multiple self-pulsating regimes and higher self-pulsating frequencies than the quasi-symmetrical mode beating.

Optical microwave/millimeter-wave links using direct modulation of two-section gain-coupled DFB lasers

Transmission of 155-Mb/s binary phase-shift-keying-modulated microwave/millimeter-wave (MMW) signal on an optical carrier over up to 80 km of standard single-mode fiber has been demonstrated experimentally using direct modulation of a two-section gain-coupled distributed feedback laser. Direct data modulation at an MMW carrier frequency of 25 GHz was enabled by on-chip optical injection locking.

Dynamics of all-optical clock recovery using two-section index- and gain-coupled DFB lasers

The dynamics of coherent clock recovery (CR) using self-pulsing two-section distributed feedback (TS-DFB) lasers have been investigated. Both simulation and experimental results indicate fast lockup and walk-off of the clock-recovery process on the order of nanoseconds. Phase stability of the recovered clock from a pseudorandom bit sequence (PRBS) signal can be achieved by limiting the detuning between the frequency of free-running self-pulsation and the input bit rate. The simulation results show that all-optical clock recovery using TS-DFB lasers can maintain a better than 5% clock phase stability for large variations in power, bit rate, and optical carrier frequency of the input data and therefore is suitable for applications in optical packet switching.

All-optical clock recovery of NRZ data at 40 Gbit/s using Fabry–Perot filter and two-section gain-coupled DFB laser

All-optical clock recovery from 40 Gbit/s non-return-to-zero (NRZ) data has been experimentally demonstrated by using a fibre-pigtailed Fabry–Perot filter and a self-pulsing two-section gain-coupled distributed feedback laser. The recovered clock has a measured root-mean-square (RMS) timing jitter of 1.2 ps. Error-free performance has been achieved in back-to-back bit error ratio (BER) tests using the optically recovered clock.

Wavelength and polarization insensitive all-optical clock recovery from 96-Gb/s data by using a two-section gain-coupled DFB laser

Wavelength- and polarization-insensitive all-optical clock recovery from data streams up to 96 Gb/s has been demonstrated by using a self-pulsing two-section gain-coupled distributed feedback laser and a semiconductor optical amplifier as a wavelength converter. The sensitivity of the clock recovery scheme is less than -10 dBm.

All-optical clock recovery from RZ-format data by using a two-section gain-coupled DFB laser

High-speed all-optical clock recovery using a two-section gain-coupled distributed feedback laser is demonstrated operating in the coherent and the incoherent modes. It is found that the coherent mode has a much better performance compared with the incoherent mode. The performance of the coherent clock recovery scheme at 12 and 40 Gb/s, including wavelength and polarization insensitivity, timing jitter, and phase noise; power penalty; sensitivity; dynamic range; locking bandwidth; detuning range of the injection wavelength; and lockup time are described in detail. A comparison between the performances of the two modes of operation is also presented.

80 Gbit/s all-optical clock recovery using two-section gain-coupled DFB laser

All-optical clock recovery from 80 Gbit/s data stream has been demonstrated using a two-section gain-coupled DFB laser. Wavelength and polarisation insensitive operation was realised by wavelength conversion using a semiconductor optical amplifier.

40 GHz millimetre-wave link based on two-sectiongain-coupled DFB lasers

Fibre transmission of a modulated 40 GHz millimetre-wave signal, optically generated from an injection-locked two-section self-pulsating gain-coupled DFB laser, is demonstrated for the first time. 155 Mbit/s phase modulated data is transmitted over 6 km of fibre with a bit error ratio of < 10-10.

Fabrication of AlGaAs-GaAs quantum-wire gain-coupled DFB lasers by a single MOCVD growth step

AlGaAs-GaAs quantum-wire (QWR) gain-coupled distributed-feedback (GC-DFB) lasers have been fabricated by a single metal-organic chemical vapor deposition growth step on 0.36-/spl mu/m pitch V-groove arrays of GaAs. A record low-threshold current of 13 mA is achieved via DFB lasing from QWR gain at room temperature. The consistency of the photon energies of the lasing and the photoluminescence peaks from QWR, and about 4-nm-wide stopband with a large threshold gain difference observed in the near-threshold spectrum are presented as possible evidence for GC-DFB effects in these devices.

Multiwavelength gain-coupled DFB laser cascade: design modeling and simulation

A theoretical investigation of a novel multiwavelength laser diode based on cascading of distributed feedback lasers is presented with consideration of the optical and the thermal-induced interactions among the different lasing sections. The design criteria and conditions for stable continuous-wave operation are established by way of simulation. The possibility and mechanism for short pulse generation as a result of mode beating are demonstrated and discussed.

Optical generation and sideband injection lockingoftunable 11–120 GHz microwave/millimetre signals

It is shown that two-section gain-coupled DFB lasers with large section lengths and weak distributed feedback coupling exhibit a self-pulsation tuning range greater than reported previously. The phase noise of a sideband injection locked self-pulsation is measured and the jitter introduced by the self-pulsing laser found to be negligible.

Laterally gain-coupled 1.57 µm DFB laserswith chromium surface grating and self-aligned Ti/Pt/Au ohmic contact

A simple method for fabricating gain coupled DFB lasers with lateral surface chromium Bragg gratings and self-aligned low capacitance ohmic contacts is reported. These InGaAsP/InP lasers show monomode emission with a sidemode suppression ratio of 40 dB. For 243 /spl mu/m long devices a continuous wave threshold current of 17 mA was measured at room temperature.

Simultaneous dual-wavelength operation in cascaded strongly gain-coupled DFB lasers

Using cascaded strongly gain-coupled (SGC) DFB lasers, simultaneous dual-wavelength operation can be obtained with better than a 40-dB side-mode suppression ratio (SMSR) under simple operating conditions at various temperatures. Dual-wavelength operation with various spacing can be achieved by grating fabrication and by simply activating the lasing section of the cascaded SGC DFB lasers. The lasing wavelengths can be tuned within several nanometers by base temperature variation and their spacing can be fine tuned by individual injection current.

Cascaded strongly gain-coupled (SGC) DFB lasers with 15-nm continuous-wavelength tuning

More than 15 nm of continuous wavelength tuning range has been obtained by means of temperature tuning and current setting in three-section grating-cascaded strongly gain-coupled distributed-feedback lasers. Within the entire wavelength tuning range, a sidemode-suppression ratio beyond 50 dB, a linewidth of less than 10 MHz, and a fiber-coupled output power of more than 5 dBm were achieved.

Matrix-grating strongly gain-coupled (MC-SGC) DFB lasers with 34-nm continuous wavelength tuning range

A matrix-grating strongly gain-coupled (MG-SGC) distributed-feedback laser structure has been demonstrated to exhibit a continuous wavelength tuning range of about 34 nm. A simple tuning mechanism was employed, and a sidemode-suppression-ratio of beyond 50 dB within the entire tuning range was achieved. This device can be potentially used in dense wavelength-division-multiplexed systems for cost effective applications.