Photomixing is a flexible and efficient method of providing both local oscillator signals for heterodyne receivers and high frequency phase reference signals. Ultrafast, 70 GHz bandwidth, λ = 1.55 μm, photodiodes from u2t Photonics AG have been incorporated into three designs of mm-wave waveguide mounts. The photomixers utilise a thin freestanding gold foil, or a gold on dielectric, probe to couple power into the waveguide and to deliver the photodiode bias. The frequency coverage of the designs is from 70 GHz to 300 GHz. A method of rapidly characterizing the frequency response of these photomixers using spontaneous-spontaneous beating of light from an EDFA is described. Recent work has been directed at increasing the degree of integration of the photodiode with the waveguide probe and choke filter to reduce the frequency dependence of the output power. A simplified photomixer block manufacturing process has also been introduced. A combined probe and filter structure, impedance matched to both the coplanar output line on the photodiode chip and to 0.4 height milled waveguide, is presented. This matching is achieved over the W-band with a fixed waveguide backshort. We present modelled and experimental results showing the increased efficiency and smoother tuning. The design and frequency response of such a probe is reported. We also present the performance of a simpler mount, operating in the frequency range from 160 GHz to 300 GHz, which generates powers of around 10 μW up to 250 GHz.
Photomixing is a flexible and efficient method of providing both local oscillator signals for heterodyne receivers and high frequency phase reference signals. Ultrafast, 70 GHz bandwidth, = 1.55 m, photodiodes from u2t Photonics AG have been incorporated into mm-wave waveguide mounts. The photomixers utilise a thin gold probe to couple power into the waveguide and a gold-on-quartz choke filter to deliver photodiode bias. A method of rapidly characterizing the frequency response of these photomixers using spontaneous-spontaneous beating of light from an EDFA is described. Recent work has been directed at increasing the degree of integration of the photodiode, waveguide probe and choke filter to reduce the frequency dependence of the output power. A simplified photomixer block manufacturing process
has also been introduced. A combined probe and filter structure, impedance matched to both the coplanar output line on the photodiode chip and to 0.4 height milled waveguide, is presented. This matching is achieved over the W-band with a fixed waveguide backshort. We present modelled and experimental results showing the increased efficiency and smoother tuning. Subsequent integration steps could use the InP photodiode substrate to support the waveguide probe
and rf filter. The design and frequency response of such a probe is presented.
Methods for the photonic generation of stable millimetre-wave reference signals are examined and compared. In particular, the generation of optical comb lines with microwave frequency separation in an amplified fibre ring and by sideband generation with an optical phase modulator are reported. Two comb lines at a millimetre-wave difference frequency can be selected using optical filters and heterodyned. The fibre ring can produce comb lines over a broad range of up to about 1 THz, whereas the sideband generation scheme is limited to frequencies of about 160 GHz. Both methods produce stable, low-phase-noise millimetre-wave signals useful as phase/frequency references.
The transmission of such reference signals through optical fibre links of up to 9 km is also investigated. Differential dispersion effects can cause a power penalty in the received millimetre-wave signal, through the interaction of chromatic dispersion and SPM/XPM effects in the fibre, and through differential polarisation changes in the fibre causing non-alignment of the two optical fields at the photodiode. For the transmission of phase reference signals, the effects of differential dispersion, both chromatic and PMD, will cause phase variations in the received millimetre-wave signal, with the PMD effect being more serious due to its stochastic behaviour.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.