Page 349 - Introduction to Information Optics

334 6. Interconnection with Optics

2.648GHZ

1.00E+009 2.00E+009 3.00E+009 4.00E-t-009 5.00E+009
Frequency (Hz)

Fig. 6.34. The frequency response of integrated MSM photodetector and polyimide waveguide
with 45 TIR mirror. The 3dB bandwidth is 2.648 GHz.

range from 9kHz to 26 GHz. The light source for frequency response
measurement is a Ti:sapphire mode-locked laser operating at 800 nm with a
pulse width of about 150fs and a repetition rate of 76 MHz. The laser power
is attenuated from its original 200 mW to 10 mW before it is coupled into the
waveguide array. An ampere meter is serially connected between the contact
probe and the biasing DC power supply. A 40 GHz ground-signal-ground
(GSG) microwave probe is used for the device contact. The biasing voltage is
provided by a DC power supply (Model E3611A, HP, Inc.) through a
100k -18 GHz biasing tee (Model 5550B, Picosecond, Inc.). The pulsed laser
light is butt-coupled into the input end of the waveguide array through a bare,
cleaved-end, single mode fiber. At the output end the guided light is reflected
from the 45° microcoupler onto the active area of the photodetector. The
optical input pulses and the complete measurement system are calibrated using
a 30 GHz bandwidth photodetector module (Model D-15, Newport, Inc.). The
3dB bandwidth of a single MSM detector is 2.648 GHz, as shown in Fig. 6.34.

6.5. INTEGRATION OF VERTICAL CAVITY SURFACE-EMITTING
LASERS (VCSELs)

We chose 850 nm to be the operating wavelength because of the availability
of high-performance vertical cavity surface-emitting lasers (VCSELs) [27].
These laser devices, compared to conventional edge-emitting lasers, offer a very