Transcript PosterEECS_time_stre.. - School of Electrical Engineering and

Jiejun Zhang
Microwave Photonics Research Laboratory, School of Electrical Engineering and Computer Science, University of Ottawa, Ontario K1N 6N5, Canada
[email protected]
2. PRINCIPLE
 High speed sampling
The implementation of powerful time stretched
sampling is jeopardized by the lack of dispersion devices
High speed sampling techniques are very important with large dispersion coefficient. This limitation is in
for many applications, such as optical waveform analogy to the magnifying factor and the aperture of a
measurement, high speed optical communication and lens imaging system. Here we proposed an fiber optic
terahertz signal sampling.
structure that can achieve the largest dispersion ever
reported, which enable us to sample electrical field at a
(c)
time resolution of 347 fs.
(a)
A microwave waveform is modulated on a predispersed optical pulse which is sent to a recirculating
dispersive loop consisting of an LCFBG and an erbiumdoped fiber amplifier (EDFA). The LCFBG is used to
achieve repetitive pulse stretching and the EDFA is used
(b)
to compensate for the loss in the loop. By controlling the
gain of the EDFA to compensate for the loop loss, the
(a) Sampled optical waveform; (b) eye diagram of an optical optical waveform can recirculate in the loop and a
communication system; (c) sampled terahertz waveform*.
repetitive use of the LCFBG for accumulated pulse
 Magnifying glass and time stretching stretching is realized.
EDFA1
MZM
PD
2X2
coupler
AWG
The magnification of a target is realized by a lens
which has a transfer function given by:
y  r   2  x    r  exp   jDr d 

2
0
The space-time duality of light indicates that
magnification can also be realized in time domain, i. e.,
very fast temporal feature of signal can be sampled by
a temporal magnifier (time stretching), with a transfer
function corresponding to that of a dispersive device:
y  t    x   t  exp   j  t d

2
Synchronization
SG
OSC
Mixer
The stretch factor is deduced as:
M  1  N C  D
By adopting the recirculating loop, an equivalent
dispersion coefficient N times as large as the original
LCFBG dispersion coefficient is achieved, and the time
stretching ability of the sampling system is enhance by N
times. In the dispersive loop, the propagation loss can be
compensated by the EDFA. Early work has demonstrated
that N can be over 200.
0
4. Experiment
To test the sampling system, an AWG in conjunction
with a signal generator is used to generate a fast
waveform (36 GHz) which exceeds the bandwidth of the
PD (20 GHz) and the real-time oscilloscope (32 GHz).
• K., Kim, etc. Petahertz optical oscilloscope. Nature Photonics, vol. 7, no. 12, pp. 958-962, Dec. 2013.
• Z. Xuan, etc. Silicon microring modulator for 40 Gb/s NRZ-OOKmetro networks in O-band. Optics Express, vol. 22, no. 23, pp. 28284-28291, Nov. 2014.
• M. Tonouchi, Cutting-edge terahertz technology, Nature Photonics, vol. 1, no. 3, pp. 97-105, Feb. 2007.
This work has been published in: J. Zhang and J. P. Yao, Optica, vol. 1, no. 2, pp. 64-69, Aug. 2014.
Figures adapted from
Voltage (mV)
OBPF
0
(c)
30
20
10
-2
-1
0
1
Time (ns)
2
30
306
(d)
20
10
921
922
923 924
Time (ns)
925
24
Voltage (mV)
MLL
20
30
20
16
12
1840
1845
1850
Time (ns)
1855
308 309
Time (ns)
310
(e)
25
20
15
926
(g)
307
1225
615 616
Time (ns)
18
14
2160
617
618
(f)
20
15
1535
(h)
2155
Time (ns)
614
25
1230
1235
Time (ns)
22
2150
613
Voltage (mV)
ATT
40
(b)
50
Voltage (mV
1
(a)
60
Voltage (mV)
EDFA2
Voltage (mV)
DC bias
DCF
The electrical signal sampled by the oscilloscope. Top: zoomed-out
waveform; lower left: zoomed-in view of the first pulse (original
pulse); lower right: zoomed-in view of the forth pulse (4 round trips).
Voltage (mV)
3
2
400 ps
Voltage (mV)
LCFBG
2 ns
Voltage (mV)
1. INTRODUCTION
According to the Nyquist-Shannon sampling theorem,
the generated signal cannot be correctly sampled by the
PD and the oscilloscope. However, by using the
dispersive loop to slow down the signal, the 20-GHz
system successfully sampled a 36-GHz signal.
1540
Time (ns)
1545
(i)
18
16
14
2455
2460
2465
Time (ns)
2470
The detail output waveforms after different number of round trips. (a)(i) correspond to 0 to 8 round trip respectively. Note that the time scale
is 1 ns/div in (a) to (d), and 5 ns/div in (e) to (i).
6. CONCLUSION
In the experiment, the electrical pulse recirculates for
8 round trips in the loop, which leads to an equivalent
dispersion coefficient of 12 000 ps/nm, which is the
largest that have ever been reported. The stretching
factor is 36, which enables the sampling of terahertz
signal with traditional electrical equipment. The
application can be numerous.