Torgil Kjellberg

A 165-Gb/s 4:1 multiplexer in InP DHBT technology

This paper presents a 4:1 multiplexer fabricated in InP DHBT technology. The multiplexer works up to 165 Gb/s. At 165 Gb/s, the chip operates at -3.2 V supply voltage and consumes 1.6 W. It is a half-rate multiplexer using a multi-phase clock architecture. The main design challenges were timing margins between clock and data.

Complete single mode wavelength coverage over 40 nm with a super structure grating DBR laser

The spectral characteristics of a widely tunable super structure grating distributed Bragg reflector (SSG-DBR) laser are investigated and the design considerations of the grating reflectors are given. By systematically adjusting the control currents of the two reflector sections and the phase section it is experimentally shown that every wavelength in an interval of 40 nm can be reached with a side-mode suppression usually better than 30 dB. >

The effect of stitching errors on the spectral characteristics of DFB lasers fabricated using electron beam lithography

Field stitching errors and their effect on the single-mode characteristics of distributed feedback (DFB) lasers fabricated using electron beam lithography were investigated. The stitching errors are associated with small-area, high-resolution electron beam exposure, which has the potential advantage of high-speed writing of laser gratings. Measurements show that the errors are composed of a systematic and a stochastic part. Their effect on the gain margin was simulated both for lambda /4 phase-shifted and optimized multiple-phase-shifted DFB lasers. Simulations show that the lasers are insensitive to the systematic part of the stitching errors if the number of errors is large enough. The stochastic part was found to give rise to a variation in gain margin of the DFB lasers. It is concluded that the field stitching accuracy in the high-resolution mode of a commercial system for electron beam lithography is sufficient to provide a high yield of single-mode lasers. However, it is essential that certain precautions be taken considering exposure conditions and that a fault tolerant laser design be used. >

A broadband differential cascode power amplifier in 45 nm CMOS for high-speed 60 GHz system-on-chip

A compact two-stage differential cascode power amplifier is designed and fabricated in 45 nm standard LP CMOS. The cascode configuration, with the common gate device placed in a separate P-well, provides reliable operating condition for the devices. The amplifier shows 20 dB small-signal gain centered at 60 GHz with a flat frequency response and 1-dB bandwidth of 10 GHz. The broadband large-signal operation is also ensured by providing constant load resistance to both stages over the entire band and coupling them with a dual resonance matching network. The chip delivers 11.2 dBm output power at 1-dB compression and up to 14.5 dBm power in saturation. The power amplifier operates with 2 V supply and draws 90 mA total current which results in 14.4% maximum PAE. The output third order intercept point is measured to be 18 dBm for two-tone measurement at 60 GHz with 0.5 GHz, 1 GHz and 2 GHz frequency separations.

Investigation on the spectral characteristics of DFB lasers with different grating configurations made by electron-beam lithography

The single-mode stability for distributed-feedback (DFB) lasers with various electron-beam-written grating configurations has been investigated theoretically and experimentally, for both as-cleaved and AR-coated lasers. Other laser properties interesting for coherent and multichannel communications systems, such as linewidth and tunability, have also briefly been investigated. Lasers with more sophisticated grating structures, such as an optimized multiple phase-shifted or a corrugation-pitch-modulated grating, did not exhibit performance significantly superior to that of lambda /4-shifted DFB lasers with an appropriate coupling coefficient. Antireflection (AR)-coating of the end facets proved indispensable for obtaining a high yield for lasers with single-mode operation at high output power and for reducing the large chip-to-chip variation seen for the as-cleaved lasers. A theoretical investigation of the effect of end reflections on the stopband and of the problem of determining the coupling coefficient was also made. >

Low-threshold grating-coupled surface-emitting lasers with etch-stop layer for precise grating positioning

The authors discuss the operation of InGaAs/AlGaAs grating-coupled surface-emitting lasers with threshold-current densities as low as 118 A/cm/sup 2/, to the best of our knowledge the lowest reported for a surface emitter. The low threshold-current density is the result of high reflectivity and low absorption gratings in conjunction with a lateral effective refractive index step in the gain section. The gratings were fabricated using electron-beam lithography and chemically assisted ion-beam etching, producing uniform rectangular gratings. A thin etch-stop layer incorporated in the epitaxial structure made it possible to combine precise control of the grating position with a strained-layer SQW-GRINSCH structure for optimum low-threshold currents.<<ETX>>

Dependence of output coupling efficiency on detuning in surface grating output couplers.

The dependence of output coupling efficiency on the periodicity of a surface grating outcoupler was investigated. Horizontal cavity InGaAs/AlGaAs laser oscillators with two first-order surface gratings as feedback elements were integrated with detuned rectangular second-order gratings as surface output couplers by the use of electron-beam lithography and chemically assisted ion-beam etching. A high surface emission efficiency of more than 60% was achieved for grating periodicities detuned -2.5 nm to -15 nm and +2.5 nm from the resonance periodicity of 295 nm. For larger positive detuning, the surface emission efficiency is reduced because of the onset of secondorder diffraction into the substrate.

DFB laser with nonuniform coupling coefficient realized by double-layer buried grating

A technique for the realization of a nonuniform grating coupling coefficient kappa , and its implementation in distributed-feedback (DFB) lasers is presented. This technique, which is an extension of the buried-grating concept, offers precise control of the coupling coefficient and enables a kappa -ratio greater than 10. DFB lasers with an asymmetric kappa -variation have been fabricated using this method. A front-to-rear facet output power ratio close to five was obtained, qualitatively in agreement with simulations.<<ETX>>

A 100-Gb/s 1:4 Demultiplexer in InP DHBT Technology

This paper presents a 1:4 demultiplexer fabricated in InP DHBT technology. The demultiplexer is verified to work up to 100 Gb/s at a supply voltage of -3.6 V consuming 2.1 W. It is a half-rate demultiplexer using multi-phase clock architecture. To verify operation up to 100 Gb/s the authors used an in-house PRBS generator chip

Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts

The single-mode stability of strained-layer MQW-DFB lasers with electron-beam written gratings containing zero, one and three phase-shifts, and with a relatively large coupling strength, has been investigated theoretically and experimentally. The fabricated lasers with the multiple phase-shifted (MPS) structure exhibited a higher degree of stability than the /spl lambda//4-shifted lasers, and a considerably improved stability for both categories with phase-shifts compared to the nonshifted lasers was obtained. These results were in good agreement with our simulations. An investigation of the linewidths of the phase-shifted lasers is also presented. The MPS lasers had a significantly lower linewidth floor (down to 600 kHz) than those with one phase-shift. There was no degradation of the side-mode suppression-ratio correlated to the linewidth floor or rebroadening. A possible explanation for the lower linewidth floors obtained for the MPS lasers is that this structure is less sensitive to inhomogeneous carrier fluctuations. Longitudinal fluctuations in the shape of the photon density distribution will thereby be suppressed. >