Gregory Fish

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.

Widely Tunable Narrow-Linewidth Monolithically Integrated External-Cavity Semiconductor Lasers

We theoretically analyze, design, and measure the performance of a semiconductor laser with a monolithically integrated external cavity. A ~4 cm long on-chip cavity is made possible by a low-loss silicon waveguide platform. We show tuning in excess of 54 nm in the O-band as well as significant reduction in laser linewidth due to controlled feedback from the external cavity. The measured linewidth in full tuning range is below 100 kHz and the best results are around 50 kHz. Approaches to further improve the performance of such laser architectures are described.

Monolithic widely-tunable DBR lasers

Tunable lasers are poised to dominate most applications areas within the next few years. Widely-tunable monolithic DBR lasers have the capability to satisfy the requirements of nearly every application area. This presentation will describe the activities to realize this goal.

Sampled-grating DBR laser-based analog optical transmitters

Sampled-grating distributed Bragg grating (SGDBR) laser-based widely tunable optical transmitters are investigated for application in high-performance analog links. More than 45 nm tuning range, 40 dB sidemode suppression ratio, and peak relative intensity noise below -153 dB/Hz is measured. SGDBR lasers integrated with semiconductor optical amplifiers and electroabsorption modulators (EAMs) are characterized with spurious free dynamic range of 125-127 dB/spl middot/Hz/sup 4/5/ over the wavelength tuning range. It is also shown how the modulation response of the EAM is affected by the optical power to limit the performance of the analog transmitter.

Harmonically Mode-Locked Hybrid Silicon Laser With Intra-Cavity Filter to Suppress Supermode Noise

We present results from two hybrid silicon mode-locked lasers, each with a 2 GHz cavity and one with an intra-cavity ring resonator filter. We compare the performance of the two lasers with respect to the harmonic mode-locking behavior at 20 GHz, i.e., the tenth harmonic. The filter based laser design passively mode-locked at 20 GHz with an electrical spur mode suppression >45 dB. Furthermore, an optical supermode suppression of 55 dB and an RF linewidth of 52 kHz was also observed. Hybrid mode-locking the laser without the filter required 10 dBm input microwave power for 25 dB (electrical) spur mode suppression as opposed to the design with the filter showing >45 dB suppression at 0 dBm input power.

Thermal effects in monolithically integrated tunable laser transmitters

We investigate thermal effects in widely-tunable laser transmitters based on an integrated single chip design. The chip contains a Sampled-Grating Distributed Bragg Reflector (SG-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA) and an electroabsorption modulator (EAM). The thermal impedance of the ridge structure is evaluated through simulation and experiment, and thermal crosstalk between sections is examined. Heating of the mirrors by neighboring sections is found to result in unintentional offsets in wavelength tuning. Thermal effects in the electroabsorption modulator are examined in depth. A positive feedback mechanism causes local temperature rise at the modulator input, with the potential to trigger catastrophic thermal runaway. A self-consistent finite-element model is developed to simulate the EAM temperature profile and device performance. This model is used to optimize the device, resulting in integrated EAMs that achieve a dissipated power limit in excess of 300 mW.

Relative intensity noise measurements of a widely tunable sampled-grating DBR laser

The intensity noise of a sampled-grating distributed Bragg reflector laser with 50-nm tuning range and 45-dB side-mode suppression ratio has been measured. The resonance frequency, damping factor, and modified Schawlow-Townes linewidth are extracted from the noise spectra. At high output power, the relative intensity noise (RIN) of the laser is below the photodiode shot noise limit, which is -160 dB/Hz. The laser has uniform shot noise limited RIN properties along the whole tuning range. The maximum resonance frequency is 5.4 GHz at a bias current of 120 mA and the K factor is 0.58 ns.

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.

Heterogeneous photonic integration for microwave photonic applications

As the component count rises in photonic systems, photonic integration becomes increasingly attractive from a cost, power consumption, and footprint perspective due to the ability to reduce the on-chip to off-chip interfaces and simplify packaging. Although photonic integration has been investigated in many forms over the last decade, the incompatibility of passive and active devices in standard integration platforms has limited their use in both military and commercial systems. In this talk, we review the advances in a heterogeneous silicon integration platform that provides state of the art active and passive devices integrated on silicon substrates for microwave systems-on-chip.

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.