Widely tunable lasers are essential components for high-capacity wavelength-division-multiplexed (WDM) transmission and photonic switching systems. For these optical fiber communication systems, they offer several advantages to increase the capacity, the functionality, and the flexibility of WDM networks. Nevertheless, these widely tunable transmitters must satisfy several stringent requirements depending on the specific application for which they are intended. Using criteria defined to compare the performances of several widely tunable laser structures reported in the literature, we pointed out a structure which presents a good tradeoff between high performances and technological processing simplicity. We designed and realized this component, the sampled-grating distributed Bragg reflector laser. Its tuning mechanism and main characteristics are first discussed. A short review is then made to compare these results to those measured on different widely tunable structures, and to propose improvements needed for practical implementation of these lasers for WDM optical fiber communications.

Widely tunable 1.55-/spl mu/m lasers for wavelength-division-multiplexed optical fiber communications

The authors describe a technique for coupling laser diode (LD) light into a singlemode fibre (SMF) which yields an efficiency as high as 85%, for uncoated micro-optics, with a working distance of 40 mu m. The 1 dB excess loss alignment tolerances are +or-0.9 and +or-4 mu m on transverse and optical axes, respectively. This is, to our knowledge, the best optimisation ever reported of the trip)et 'coupling efficiency, working distance, and alignment tolerances' for an uncoated fibre micro-optics arrangement. >

High efficiency, long working distance laser diode to singlemode fibre coupling arrangement

Single-mode operation with output power up to 100 mW is reported for the first time for InGaAsP-InP DBR lasers. These devices exhibiting a record 17-nm tuning range, have been realized using a three-step MOVPE process. The output power variations under tuning are limited to about 1.5 dB, and the tuning range remains quasiconstant with the output power. Using a two-wavelength DBR laser array with Bragg wavelengths spaced by 15 nm, 61 channels regularly spaced by 0.5 nm are accessible by controlling only two currents. Moreover systematic investigations of accelerated aging of these components have been realized for the first time. For all the tests performed on both active and tuning sections, no spectral degradations are observed, and the tunability remains unchanged. To define the lifetime of a tunable laser, e.g., a DBR laser, we propose a new failure criterion based on both active operating current and wavelength degradations. Using this criterion, the lifetime at 60/spl deg/C is estimated to be more than 7/spl middot/10/sup 4/ h, and is not limited by the wavelength degradation, but effectively by the operating current degradation.

High reliability of high-power and widely tunable 1.55-/spl mu/m distributed Bragg reflector lasers for WDM applications

To investigate physical mechanisms involved in long-term wavelength drift of tunable distributed Bragg reflector (DBR) laser, the evolution of the tuning characteristics as well as the Bragg section intensity modulation response of several DBR lasers have been simultaneously assessed by current injection in the Bragg section only. Current versus voltage I(V) characteristics under aging have also been recorded to compare the role of leakage current and nonradiative recombination defect evolution. The wavelength drift as well as the carrier lifetime of the tuning section varies following an exponential law A+Bexp(-t/sub A///spl tau/) versus aging time t/sub A/. The time constant /spl tau/ is aging temperature and Bragg current dependant. The carrier lifetime decreases with time indicating a wavelength drift mainly due to nonradiative recombination defect increase. Modeling of the I/sub B/(V) and /spl lambda//sub B/(I/sub B/) characteristics is presented, that fits nicely the experimental data. The exponential form of the wavelength drift is used to propose novel and adequate burning conditions of DBR lasers.

Long-term wavelength stability of 1.55-/spl mu/m tunable distributed Bragg reflector lasers

Singlemode operation with an output power of up to 100 mW is reported for the first time for InGaAsP-InP DBR lasers These devices exhibiting a record 17 nm tuning range, have been realised using a three-step MOVPE process The output power variations under tuning are limited to /spl sim/15 dB, and the tuning range remains quasi-constant with output power

High power operation of widely tunable 1.55 [micro sign]m distributed Bragg reflector laser

A pigtailed transceiver module which exhibits a record responsivity of 0.5 A/W is described. A single laser chip of Fabry-Perot type V-on-U-groove (VUG) laser is packed in a butterfly type package. By improving the fibre-chip coupling, a responsivity as high as 0.5 A/W is demonstrated together with a bandwidth of 1.5 GHz. The power penalty, compared with that of a p-i-n photodiode within the same experimental configuration, is only 1.2 dB at 800 Mbit/s. >

High responsivity 1.3 μm transceiver module for low cost optical half-duplex transmission

Compact modules comprising a DBR laser and a GaAs IC-driver have been realised for ATM optical switching. These modules, designed to switch between four preset wavelength channels, show fast switching times of 12 ns over 12 wavelengths regularly spaced by 0.3 nm. Owing to the high tuning efficiency of the DBR laser, these results are obtained while the power consumption of the driver is kept as low as 0.8 W.

J. Semo

Papers

High responsivity 1.3 μm transceiver module for low cost optical half-duplex transmission

12 wavelength channel fast switching operation of compact DBR laser modules including IC-drivers