T. Wipiejewski

Widely tunable electroabsorption-modulated sampled-grating DBR laser transmitter

We report on a widely tunable transmitter based on a sampled-grating distributed Bragg reflector (SG-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA) and an electroabsorption (EA) modulator. Modulated time-averaged powers in excess of 5 dBm, RF extinction ratios >10 dB, and error-free transmission at 2.5 Gb/s for 350 km of standard single-mode fiber have been demonstrated across a 40-nm tuning range. In CW mode of operation, the module meets all long-haul system requirements for externally modulated laser sources: stability, power (>10 mW), RIN ( 100 yr for output wavelength stability and power across all channels.

Evaluating the effects of optical and carrier losses in etched‐post vertical cavity lasers

We demonstrate the combined effects of optical scattering loss and surface recombination (or carrier diffusion) on the performance and scalability of etched‐post vertical cavity lasers (VCLs). The size dependence of optical losses and threshold gain are determined from pulsed measurements of external quantum efficiency. Deeper etch depths result in a stronger radial dependence of the threshold gain, which quickly increases the threshold current density. With optical loss accounted for, pulsed threshold current density measurements give the extra information needed for evaluating carrier loss. Surface recombination or carrier diffusion also results in threshold current density increases, but scalability is ultimately limited by the ability of the active region to provide enough gain for smaller size, higher optical loss devices. Even with these losses, three‐quantum‐well VCLs with shallow etches have threshold currents as low as 420 μA.

Thermal crosstalk in 4 x 4 vertical-cavity surface-emitting laser arrays

We measured thermal crosstalk in 4/spl times/4 VCSEL arrays with a 30-/spl mu/m pitch between devices. The effective thermal resistance of laser diodes in two-dimensional (2-D) arrays is about 50% higher than that of single elements. The output power of the lasers is fairly temperature insensitive under constant voltage operation. From experiments we inferred values for the average thermal conductivity of AlAs-GaAs Bragg reflectors. We found anisotropy in the effective thermal conductivity with numbers of 0.28 W/(cmK) and 0.35 W/(cmK) for the transverse and lateral direction, respectively.

Size-dependent output power saturation of vertical-cavity surface-emitting laser diodes

We demonstrate efficient vertical-cavity surface-emitting laser diodes with high output power levels. Improved output power in these pillar-etched devices is achieved through a 60% lower thermal resistance by using a 15-/spl mu/m-thick Au-plated heat spreading layer on the top surface with a size of 300/spl times/300 /spl mu/m/sup 2/. The maximum continous wave output power increases almost linearly with laser diameter, before it saturates at 42 mW for an unmounted Au-plated device of 64-/spl mu/m diameter. A simple analytical model describes the laser output characteristics and the size-dependent saturation behavior of the maximum output power.

High performance widely-tunable SG-DBR lasers

Widely-tunable sampled-grating distributed Bragg reflector (SG-DBR) lasers with integrated Semiconductor Optical Amplifiers (SOAs) simultaneously exhibit high (20 mW CW) fiber-coupled output power, high side mode suppression ratio, low noise (below -140 dB/Hz RIN), low line-width (<5 MHz), and high reliability, across a 40 nm C-band tuning range.

Widely-tunable electroabsorption-modulated sampled grating DBR laser integrated with semiconductor optical amplifier

Summary form only given. We have demonstrated a widely-tunable, 2.5 Gb/s transmitter based on a SG-DBR laser monolithically integrated with a SOA and electroabsorption modulator. Time-averaged powers in excess of 3 dBm and RF extinction ratio >10 dB across a 40 nm tuning range have been achieved. Error-free transmission at 2.5 Gb/s has been demonstrated for 200 km of standard single mode fiber.

Integration of active optical components

Integration of active optical components typically serves five goals: enhanced performance, smaller space, lower power dissipation, higher reliability, and lower cost. We are manufacturing widely tunable laser diodes with an integrated high speed electro absorption modulator for metro and all-optical switching applications. The monolithic integration combines the functions of high power laser light generation, wavelength tuning over the entire C-band, and high speed signal modulation in a single chip. The laser section of the chip contains two sampled grating DBRs with a gain and a phase section between them. The emission wavelength is tuned by current injection into the waveguide layers of the DBR and phase sections. The laser light passes through an integrated optical amplifier before reaching the modulator section on the chip. The amplifier boosts the cw output power of the laser and provides a convenient way of power leveling. The modulator is based on the Franz-Keldysh effect for a wide band of operation. The common waveguide through all sections minimizes optical coupling losses. The packaging of the monolithically integrated chip is much simpler compared to a discrete or hybrid solution using a laser chip, an SOA, and an external modulator. Since only one optical fiber coupling is required, the overall packaging cost of the transmitter module is largely reduced. Error free transmission at 2.5Gbit/s over 200km of standard single mode fiber is obtained with less than 1dB of dispersion penalty.

Performance and reliability of widely tunable laser diodes

We are manufacturing widely tunable laser diodes based on an integrated single chip design. The sampled-grating distributed Bragg reflector (SG-DBR) laser is monolithically integrated with a semiconductor optical amplifier (SOA). The continuous wave (cw) output power of the fully packaged device is more than 2OmW over the entire C-band with low noise figures and a high side-mode suppression ratio of over 40dB. Devices are made for L-band operation as well. The devices are well suited for long-haul and ultra-long-haul DWDM optical transport systems. For metro type applications we developed an EML-type device with a SG-DBR widely tunable laser monolithically integrated with an SOA and an electro-absorption modulator (EAM) based on the Franz-Keldysh effect. The operating speed is 2.7GbiVs for OC-48 systems including forward error correction (FEC). The time averaged output power is in excess of 5dBm over the 4Onm C-hand tuning range. The extinction ratio is larger than IOdJ3:Error free transmission over more than 350km of standard single mode fiber is demonstrated. Wavelength switching is accomblished in less than lOms which is limited by the control electronics. The monolithically integrated widely tunable SG-DBR lasers show excellent reliability and environmental stability results. After testings hundreds of devices over several thousands of hours a long wear-out lifetime of over 350 years has been inferred with a very low failure rate of less than IOOFITs over the normal operating lifetime. The results indicate no reliability penalty for wavelength tunability compared to standard fixed wavelength DFB lasers.

Monolithic integration of a widely tunable laser diode with a high speed electro absorption modulator

We are manufacturing widely tunable laser diodes with an integrated high-speed electro-absorption modulator for metro and all-optical switching applications. The monolithic integration of the device combines the functions of high power laser light generation (>10 mW), wavelength tuning over the entire C-band (>100 channels on 50 GHz grid), and high speed signal modulation (>2.5 Gbit/s). The laser section of the chip contains two sampled grating DBRs with a gain and a phase section between them. Wavelength tuning is achieved by current injection into the waveguide layers of the DBRs. Since electronics tuning and not thermal or mechanical tuning is employed wavelength tuning can be easily performed on a short time scale of less than 10 ms which is required for various applications. Even 40 ns tuning speed is feasible with the appropriate driver electronics. Transmission experiments show less than 1 dB power penalty over 200 km of standard single mode fiber for all channels.

High performance vertical-cavity surface-emitting laser diodes with a Au-plated heat spreading layer

Etched-pillar vertical-cavity surface-emitting laser diodes exhibit submilliamp threshold currents down to 400 /spl mu/A and high output power levels. A Au-plated heat spreading layer reduces the thermal resistance by a factor of two and increases the maximum output power by approximately 60%. A laser with 660 /spl mu/A threshold current reaches a maximum output power of 3.56 mW. The good heat sinking provides high output power despite relatively large operating voltages over 3 V. Small output power variations over a wide temperature range from 20/spl deg/C to 90/spl deg/C are demonstrated. The best temperature insensitivity of laser output power is achieved in a constant voltage operation mode.