Time-Domain Terahertz - Toptica

Photomixerscw Terahertz Generation with Leading-Edge TechnologyHaving teamed up with some of the world’s leading terahertz research institutes,TOPTICA is the only company worldwide that is able to offer top-quality GaAs andInGaAs photomixers. Both material systems have their own merits. GaAs photomixersprovide high bandwidths and a superior dynamic range when used in a coherenttransmitter-receiver configuration. InGaAs emitters, on the other hand, generatepower at record levels and take advantage of mature yet inexpensive 1.5 µm telecomtechnology.All of TOPTICA’s photomixer modules come equipped with a Silicon lens, an electricconnector and SM/PM fiber pigtail. The all-fiber design enables an easy and flexibleintegration into any terahertz assembly.Key features· GaAs (850 nm) and InGaAs(1550 nm) photomixers· Fully-packaged modules withSM/PM fiber pigtail· Signal-to-noise ratio up to 80 dBApplications· High-resolution terahertzspectroscopy· Combustion analysis, semiconductorstudies, non-destructive testingHighest bandwidths with GaAs photomixersBased on a planar structure, GaAs photomixers comprise an interdigitated fingerstructure at the center and a surrounding broadband antenna. The bandgap of thesemiconductor calls for excitation wavelengths below 870 nm. To efficiently generateterahertz radiation, the chip design relies on “defect engineering” techniques: Lowtemperaturegrowth, the integration of ErAs nanoclusters or ion bombardment reducesthe recombination times of the photoelectrons.TOPTICA’s GaAs photomixers achieve an outstanding bandwidth of 3 THz and dynamicranges as high as 80 dB at 100 GHz, or 60 dB at 1000 GHz.Terahertz power (µW)1010.10.011E-31E-40 500 1000 1500 2000Frequency (GHz)2µmlight300nm20µmmetalp-contact(i) absorbern-contactwaveguideOutput power of an InGaAs photodiodeemitter.Cross-section of an InGaAs photodiodeemitter with integrated waveguide.(Fraunhofer Heinrich-Hertz Institute,Berlin / Germany)2800Dynamic range (dB)604020Integration time 300 msIntegration time 2.6 ms00 500 1000 1500 2000Frequency (GHz)V −V+Optical beatMetallizationActive layerV+ V− V+V−Semi-insulating substratePhotocurrent (mA)-2-4Laser power-60 mW10 mW-820 mW30 mW-10-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0DC bias (V)Dynamic range of GaAs photomixers,used in a coherent emitter-receiverconfiguration. The dips are absorptionlines of water vapor.Top view (left) and cross section(right) of a planar photomixer withinterdigitated finger structure. V+ andV- denote the bias voltage.Photocurrent vs. bias voltage of anInGaAs photodiode emitter.