Direct modulation of widely tunable twin-guide lasers

The possibility to directly modulate widely tunable lasers up to several gigahertz is desirable in telecom applications. We discuss the dynamic properties of the recently proposed widely tunable twin-guide laser concept. It has promising prospects with a maximum theoretical bandwidth above 20 GHz and the 3-dB bandwidth at 250 mA indicates that an actual bandwidth of 12 GHz should be possible. The current lasers were not designed for high-speed modulation, so only 1-GHz modulation can be reached at the moment.     

Improvement of the wavelength switching behavior of semiconductor tunable lasers through optical feedback from a periodic reference filter based on a novel prism-based implementation of a Fox-Smith resonator

We show that the wavelength switching behavior of semiconductor tunable lasers can be improved through optical feedback from a stable reference filter. The filter is based on a novel prism-based implementation of a Fox-Smith resonator and has a response consisting of periodically spaced peaks, both in reflection and transmission. The improvement of the wavelength switching behavior stems from the suppression of the thermally induced wavelength drift associated with the switching of the tuning currents.     

The influence of lateral carrier diffusion and surface recombination on the behavior of semiconductor optical amplifier (SOA)-based MMIs

The influence of lateral carrier diffusion and surface recombination on the self-imaging properties of semiconductor-optical-amplifier-based multimode interference couplers has been verified by simulations using a beam propagation method. It shows a significant degradation of the self-imaging properties of these devices. Buried heterostructures or deeply etched waveguide structures can decrease the impact when the degree of surface recombination is sufficiently low.     

All-Optical Flip-Flop Based on an SOA/DFB-Laser Diode Optical Feedback Scheme

We report on the dynamic all-optical flip-flop (AOFF) operation of an optical feedback scheme consisting of a semiconductor optical amplifier (SOA) and a distributed feedback laser diode (DFB-LD), bidirectionally coupled to each other. The operation of the AOFF relies on the interplay between the optical powers in both the DFB-LD and the SOA. Switching times as low as 150ps for switch pulse energies of around 6 pJ and a repetition rate of 500MHz have been measured. The contrast ratio was measured to be above 12 dB     

Control of widely tunable SSG-DBR lasers for dense wavelengthdivision multiplexing

This paper presents a general discussion on the control of widely tunable super structure grating distributed Bragg reflector (SSG-DBR) lasers. A feedback control scheme is presented that ensures frequency stability and accuracy (better than ±0.5 GHz), as well as high side mode suppression ratio (>35 dB). The active section voltage is monitored to maintain mode stability and a highly stable Fabry-Perot etalon is used as a reference to lock the laser frequency to a specific ITU channel. It is shown that stability can even be maintained when directly modulating the laser at 1.244 Gb/s. Furthermore, a characterization scheme is demonstrated that uses the voltage monitoring to generate a look-up table of operation points very efficiently and accurately. For all operation points, the frequency accuracy is better than ±0.5 GHz and the side mode suppression ratio is above 35 dB     

Experimental demonstration of all-optical regeneration using anMMI-SOA

A novel all-optical 2R regenerator based on a multimode interference coupler (MMI) semiconductor optical amplifier is presented. Static measurements of the transfer function reveal a digital transfer characteristic and a high increase in extinction ratio. The experiments are in good agreement with simulations, which have been done using a modified beam propagation method program. The device has a high tolerance to the MMI length. It has been fabricated in an all-active layout, avoiding the need for active/passive integration and is very compact     

Extended modulation bandwidth of DBR and external cavity lasers byutilizing a cavity resonance for equalization

We have investigated the occurrence of a second resonance frequency in distributed Bragg reflector laser diodes and the high modulation bandwidth resulting from it. The influence of different laser parameters has been theoretically investigated. It is also shown that a similar behavior can be obtained in laser diodes with a passive, low-loss, and gratingless external cavity. The possibilities of large-signal digital modulation are also investigated     

Wide wavelength tuning of sampled grating tunable twin-guide laser diodes

Tuning characteristics of widely tunable twin-guide (TTG) laser diodes with sampled gratings (SGs) are reported. Two SGs, providing slightly different reflection spectra, enable wide tunability by means of Vernier effect tuning. The device structure is vertically integrated and, hence, a DFB-like laser is obtained, which makes a phase tuning section unnecessary and facilitates easy and fast device characterisation. Although the tuning section can tune the SG reflection spectra by only /spl sim/2 nm, an overall tuning range of 28 nm has been achieved by employing Vernier effect tuning. Within the aforementioned tuning range, five supermodes are usable and can be tuned continuously without any mode-hops. The lasers operate at /spl sim/1.55 /spl mu/m wavelength and achieve a maximum output power of 12 mW.     

Coupling coefficients in gain-coupled DFB lasers: inherent compromise between coupling strength and loss

A theoretical analysis of the gain-coupling coefficient for distributed feedback (DFB) lasers with first-order, rectangular, gain, or loss gratings is presented. For the structure with gain grating, the dependence of the gain-coupling coefficient on the modal gain has been taken into account for the first time. In both structures, an inherent compromise between coupling strength and extra modal loss is found. The results show that significant gain-coupling coefficient values are feasible.<>     

Athermal arrayed waveguide gratings in silicon-on-insulator by overlaying a polymer cladding on narrowed arrayed waveguides

Athermal arrayed waveguide gratings (AWGs) in silicon-on-insulator (SOI) are experimentally demonstrated for the first time to our knowledge. By using narrowed arrayed waveguides, and then overlaying a polymer layer, the wavelength temperature dependence of the AWGs is successfully reduced to -1.5 pm/°C, which is more than 1 order of magnitude less than that of normal SOI AWGs. The athermal behavior of the AWGs is obtained with little degradation of their performance. For the central channel, the cross talk is less than -15 dB and the insertion loss is around 2.6 dB. Good characteristics can be maintained with temperatures up to 75 °C. The total size of the device is 350 μm × 250 μm.