L.J.P. Ketelsen

40-Gb/s tandem electroabsorption modulator

In this letter, we have developed a tandem electroabsorption modulator with an integrated semiconductor optical amplifier that is capable of both nonreturn-to-zero and return-to-zero (RZ) data transmission at 40 Gb/s. The tandem modulator consists of a broad-band data encoder and a narrow-band pulse carver. The pulse carver is able to produce 5-ps pulses with more than 20 dB of extinction. The on-chip semiconductor optical amplifier provides up to 8.5 dB of fiber-to-fiber gain and enables the modulator to be operated with zero insertion loss. Devices have been realized with greater than 40-GHz bandwidth, and 13-dB dynamic extinction for a 2.5-V swing. For optimized designs bandwidths of nearly 60 GHz: have been realized. Using these devices penalty free RZ data transmission over a 100-kin dispersion compensated fiber link has been demonstrated with a received power sensitivity of -29 dBm.

40 Gb/s tandem electro-absorption modulator

NRZ and RZ data transmission at 40 Gb/s are demonstrated for the first time using buried heterostructure tandem electro-absorption modulators monolithically integrated with a semiconductor optical amplifier and input/output spot-size converters. Zero penalty RZ transmission over a 100 km dispersion managed link is achieved.

40 Gb/s photonic integrated receiver with -17 dBm sensitivity

We report on the design, fabrication and characterization of a novel 40 Gb/s optical receiver. The device consists of a high-speed waveguide photodiode monolithically integrated with a semiconductor optical amplifier to create a fully photonic receiver. We have achieved a back-to-back receiver sensitivity of -17 dBm for NRZ data transmission at 40 Gb/s. When used with an erbium doped fiber preamplifier a sensitivity of -32 dBm or 123 photons/bit has been realized for RZ transmission with -6 dBm input power at the receiver. The device has a small signal bandwidth of 39 GHz and a conversion gain of more than 800 Volts per Watt.

Chapter 12 – Telecommunication Lasers

Publisher Summary It is noted that semiconductor diode lasers have undergone years of refinement to satisfy the demands of a wide range of telecommunication systems that includes performance, reliability, and cost. To be specific, long-haul terrestrial and undersea systems demand reliability, speed, and low chirp, short-reach systems demand low cost, and finally analog cable TV systems demand high power and linearity. The history, the basic elements of device design and function, the applications, and the essential fabrication techniques of telecom lasers have been illustrated in the chapter. The four major classes of telecom lasers include analog, directly modulated, electroabsorption modulated, and wavelength-selectable. It is observed that many R&D institutions are developing low-capacitance device architectures to extend the device structures upto 40 Gb/s and beyond. It is also noted that along with higher functionality comes issues such as increased monolithic integration, need for closed loop electronic control, and architectural uncertainty. All of these issues, essentially, led to the development of tunable lasers.

40Gb/s tandem electro-absorption modulator

NRZ and RZ data transmission at 40Gb/s are demonstrated for the first time using buried heterostructure tandem electro-absorption modulators monolithically integrated with a semiconductor optical amplifier and input/output spot-size converters. Zero penalty RZ transmission over a 100km dispersion managed link is achieved.

Integrated photonic devices for fiber optic communication systems

Fabrication and epitaxial growth technology for III-V semiconductor devices have developed to the point where substantial levels of photonic integration are now feasible. Both highly complex and simple photonic integrated devices are currently the subjects of much active research and product development. These efforts are motivated by the many potential advantages of photonic integration, reduced size, lower power consumption, increased functionality, higher performance and above all else lower cost. We discuss two different examples of photonic integrated devices that demonstrate some of the significant performance advantages that can be achieved with this technology. Both devices are fabricated using our deep ridge buried heterostructure technology that combines both SAG and butt joint epitaxial techniques to obtain the maximum flexibility in the device design. The first device is a high-speed modulator with an integrated phase shifter that enables the transmitter chirp to be dynamically tuned. This enables the transmission performance to be optimized for different amounts of fiber dispersion. In this device the phase shifter can be driven either with a synchronous sinusoidal source or a complementary data modulation. By varying either the amplitude of the drive signal or the bias on the phase modulator the chirp of the transmitted optical pulses can be controlled. For synchronous sinusoidal or narrowband chirp control a single frequency drive signal synchronized with the data modulation is applied to the phase modulator. This signal can be used to apply either positive or negative chirp to the transmitted data bits by varying the phase and amplitude of the drive signal. A more sophisticated approach uses the complement of the data modulation signal to drive the phase modulator. This method referred to as broadband chirp control provides better compensation since it applies frequency chirp only to the transitions in the signal.

A practical approach to wavelength selectable DWDM sources

A wavelength selectable source within a transmitter for high-speed, dense wavelength division multiplexed systems must tune across a substantial number of channels while meeting rigorous system specifications in each channel. It must offer the same level of stability, reliability and ease of use as single wavelength counterparts. We examine a tunable source designed to meet the needs of high bit-rate DWDM systems for long-haul and metro applications.

Fully functional integrated tunable and stabilized lasers and transmitters for DWDM applications

Tunable lasers are becoming critical in DWDM systems for reasons of increased system functionality, system adaptability and costs. Key issues that arise are wavelength tuning range, characterization of the devices, wavelength control, mode stabilization, wavelength switching times, output power and long term stability of operation. We have developed tunable EML components and transmitters that address all these issues. Transmission at 2.5 Gb/sec over 640 km of fiber has been demonstrated using an EA-DBR capable of being tuned to any one of 20 wavelengths spaced at 50 GHz. These lasers are integrated into a single package with wavelength stabilization elements and can be stabilized such that both the desired wavelength and mode are maintained during operation. These integrated modules are also incorporated into a small form factor transmitter capable of operating in DWDM systems.

High-power tunable DBR lasers for digital communication systems

High power buried heterostructure 1.55micrometers tunable DBR lasers have been designed, fabricated and characterized. The laser consists of a gain section, a distributed Bragg reflector, a semiconductor optical amplifier and front photodetector for automated power control. The heterostructures were grown by MOCVD with the help of selective area growth techniques and dual waveguide heterostructure. Several advantages stem from this integration scheme which include simplicity of design and fabrication, increased reliability and low cost. The laser exhibits output power of 13dBm in the fiber and is tunable over 30(50GHz) ITU channels. The laser exhibits excellent performance and long-term control and reliability. The laser/transmitter also demonstrates significant increase of its functionality while its size remains small.

40-Gb/s electroabsorption-modulated NRZ and RZ sources

Electro-absorption modulated sources are likely to be key components in the evolution of optical communication line rates from 10Gb/s to 40 Gb/s. Compared with the LiNbO3 alternative EA modulators are more compact, less expensive, compatible with monolithic integration, and offer lower drive voltages. However, fabrication complexity and open questions concerning the fidelity with which they transmit information make the exact role of 40Gb/s EA modulators in advanced communication systems somewhat unclear. In this talk we will describe the design, fabrication and transmission performance of 40Gb/s EA modulators configured for both NRZ and RZ operation. For NRZ transmission the device structure consists of a short MQW modulator with spot-size converters on the input and output ends. Tandem EA modulators for pulse carver and data encoder functions were monolithically integrated along with a semiconductor optical amplifier and input/output spot-size converters to explore RZ transmission. Both single and tandem modulator design are realized using semi-insulting InP current confined buried heterostructure technology. Modulation bandwidth of better than 50 GHz is demonstrated along with a fiber-to-fiber insertion loss of less than 6 dB for the single modulator design. The carver/encoder configuration with onboard SOA yields better than 0 dB insertion loss. Transmission impairments were studies using both designs.