Optical modulation in a resonant tunneling relaxation oscillator

Abstract

We report high-speed optical modulation in a resonant tunneling relaxation oscillator consisting of a resonant tunneling diode ͑RTD͒ integrated with a unipolar optical waveguide and incorporated in a package with a coplanar waveguide transmission line. When appropriately biased, the RTD can provide wide-bandwidth electrical gain. For wavelengths near the material band edge, small changes of the applied voltage give rise to large, high-speed electroabsorption modulation of the light. We have observed optical modulation at frequencies up to 14 GHz, associated with subharmonic injection locking of the RTD oscillation at the fundamental mode of the coplanar transmission line, as well as generation of 33 ps optical pulses due to relaxation oscillation.

Optical modulation at around 1550 nm in an InGaAlAs optical waveguide containing an InGaAs/AlAs resonant tunneling diode

“…A maximum modulation depth of 28 dB was obtained at 1565 nm, which is approximately 10 dB higher than the maximum obtained with a GaAs/AlAs device. 5 In conclusion, optical modulation up to 28 dB has been demonstrated in InGaAlAs optical waveguides containing an InGaAs/AlAs double-barrier resonant tunneling diode ͑RTD͒, due to peak-to-valley switching. Integration of a RTD with an optical waveguide, which combines a wide bandwidth electrical amplifier with an electroabsorption modulator, opens up the possibility for a variety of operation modes ͑such as modulation due to self-oscillation and relaxation oscillation͒.…”

“…Previously, we reported work on an GaAs/AlAs RTD that was successfully integrated in a unipolar GaAs-AlGaAs optical waveguide, 4 and high-speed optical modulation ͑up to 18 dB͒ combined with electrical gain was demonstrated. 5 This device operated around 900 nm. For devices functioning at the usual optical communication wavelengths, 1300 or 1550 nm, applications could include, for example, optical distribution of modulated millimeter-wave frequency carriers for mobile communication systems.…”

“…The modulation depth can be considerable because, under certain conditions, the RTD operation point switches well into the two positive differential resistance portions of the current-voltage ͑I-V͒ characteristic, with a substantial part of the terminal voltage dropped across the depleted region in the collector side. 5,6 The advantage of the RTD-EAM compared to conventional pn modulators is that, when dc biased close to the negative differential conductance ͑NDC͒ region, the device behaves as an optical waveguide electroabsorption modulator integrated with a wide bandwidth electrical amplifier.The high-frequency and large modulation depth characteristics of the RTD-EAM are a direct consequence of the carrier transport mechanisms across the RTD and the waveguide depletion region. They are closely related to the material system and the specific device structure.…”

Electric field switching in a resonant tunneling diode electroabsorption modulator

“…Streak camera studies of our GaAs RTD-EAM demonstrated 30 ps pulses of light and self-oscillation at up to 16 GHz which analysis of the design suggested it was limited by the electronic packaging [9] [14]. A similar streak camera investigation of the InAlGaAs RTD-EAM high-speed characteristics could not be undertaken because of the low radiant sensivity of the streak tube at 1550 nm.…”

“…The wavelength of operation is set by the band-gap of the material employed in the active region (waveguide core) of the device. Our initial devices used GaAs in the active region (see [8] [9]) and operated at 900 nm, subsequently In 0.53 Ga 0.42 Al 0.05 As was employed to shift the wavelength of operation to 1550 nm (InGaAlAs was used because it is a convenient semiconductor alloy for MBE growth. )…”