Frequency Combs - TOPTICA Photonics AG

Frequency Combs - TOPTICA Photonics AG
Frequency Combs
Inherently CEP-stable
Optical Clocks
Microwave Generation
High-resolution Spectroscopy
Laser Reference
Dual-comb Spectroscopy
Direct Frequency Comb Spectroscopy
CEP-stable Seeders
Frequency Combs
Frequency combs are very precise tools
a regular train of ultrashort laser pulses in
freedom, fCEO and frep, are stabilized to a
which are used for applications that re-
the time domain. Such output characte-
frequency reference. The discrete spec-
quire highest accuracy and resolution
ristics can be generated from a standard
trum adopts the absolute stability of the
when measuring the frequency of light.
mode-locked laser oscillator. The discrete
reference and can therefore be used as
A frequency comb has an optical spec-
lines of the spectrum are separated by
an “optical ruler”. The performance of a
trum that consists of equidistant lines in
the repetition rate frep of the laser pulses.
frequency comb is thus entirely given by
the frequency domain. These lines ser-
In addition, the so called carrier-envelope
the choice of reference and the ability to
ve as reference to measure unknown
offset frequency fCEO is given by the off-
stabilize its phase and frequency fluctua-
frequencies or to stabilize a laser to a
set of the periodic spectrum from zero.
tions to this reference.
certain frequency. The discrete spectrum
A mode-locked laser is usually called a
in the frequency domain corresponds to
frequency comb when both degrees of
Standard comb - frequency and time domain
FT(E)
frep= 1/∆t
fCEO= ∆ ϕCE/ 2π ∆t
E(t)
FT(E)
fn=fCEO+ nfrep
ϕCE(t1)
Frequency (Hz)
ϕCE(t2)
ϕCE(t3)
frep= 1/∆t
Time (s)
∆t
fCEO= ∆ ϕCE/ 2π ∆t
fn=fCEO+ nfrep
Frequency (Hz)
feedback loop to compensate for phase
the actuators used for stabilizing fCEO
and frequency fluctuations. Their perfor-
CE 3
i.e. they
and frep are not fully decoupled,
ween the
envelope and carrier of subseFT(E)
quent pulses, the carrier envelope phase
mance is limited by the finite bandwidth of
have an effect on both parameters.
the electronic feedback circuit.
(CEP) φCE. The typical method to stabilize
As a∆t
result, high frequency phase noi-
In practice, this means that if one parameTime (s)
ter is tightly locked to a reference, the
A non-zero carrier-envelope offset freis caused by a phase slip betquency fCEOE(t)
ϕCE(t1)
fCEO
f in=a 0standard comb relies on complex
CEO
self-referencing
methods and an active
frep= 1/∆t
ϕ
CE
E(t)- frequency and time domain
DFC comb
ϕCE(t2)
ϕ (t )
se cannot be corrected. Another disad-
other suffers from additional unwanted
vantage of this method is that usually
broadening.
Frequency (Hz)
= const.
FT(E)
Time (s)
fCEO= 0
frep= 1/∆t
E(t)
Frequency (Hz)
ϕCE = const.
Time (s)
2
CERO Principle & Applications
The CERO principle relies on Difference Frequency Generation between two spectral parts of a broad supercontinuum:
fm- fn = (m frep+ fCEO) - (n frep+ fCEO) = (m-n) frep
CERO: Inherently noise-free
TOPTICA’s unique difference frequency comb DFC implements the completely passive CERO technology, which
inherently stabilizes fCEO and the carrier
envelope phase. The DFC is the first
commercial
superior
system
patented
based
on
technology
this
(patent
number: DE102004022037). The fiberbased comb combines the convenience
and robustness of fiber lasers with low-noise performance.
frequency parts of the spectrumin a non-
spectrum. Additionally, the fCEO of the comb
frequency combs relies on a more than
linear optical crystal. This results in a new
is fixed to zero. All TOPTICA frequency
octave-spanning super-continuum gene-
frequency comb at 1560 nm with a simpli-
comb systems employ this so called CERO
rated from of a low noise Er-fiber mode-
fied and reliable, all-passive fCEO stabilization.
technology (“zero-fCEO”). To stress the im-
locked oscillator at 1560 nm and sub-
The new comb is free from fluctuations of
portance of the DFG process, TOPTICA’s
sequent difference frequency generation
the CEP and fCEO due to the common mode
frequency comb product line is named
(DFG) between certain low- and high-
suppression of the two parts of the original
DFC: Difference Frequency Combs.
Oscillator
Spectral Power [dB]
The operating principle of TOPTICA’s
frep Controller
Amp
Generation of special supercontinuum
spanning 193 THz in a highly nonlinear fiber. Both spectral parts have
identical fCEO.
HNLF
Optical Power [dBm]
Low noise Er-fiber oscillator at
1560 nm. Ultrafast fiber technology
proven since 2004.
Low-noise oscillator
-10
-20
-30
-40
-50
-60
15
1
1
1
1
1
1
00 520 540 560 580 600 620
Wavelength [nm]
HNLF
-20
-30
-40
-50
800
1000
fm=(m frep + fCEO)
1200
1400
1600
Wavelength [nm]
1800
2000
fn=(n frep + fCEO)
Difference frequency generation
between parts of supercontinuum in
nonlinear crystal. The resulting comb
at 1560 nm is CEP stabilized, fCEO
is fixed to zero, fCEO and frep are
completely decoupled.
Difference
Frequency
Generation
Amp
Spectral Power [dB]
(c/850 nm + fCEO) - (c/1860 nm + fCEO) ≈ c/1560 nm
-20
Offset-free comb
-25
-30
-35
fm-fn=(m-n) frep
-40
1400 1450 1500 1550 1600 1650
Wavelength [nm]
3
Difference Frequency Comb (DFC)
Modular Concept
TOPTICA’s frequency comb product line
available to provide RF beats between
is a modular system that supports a bro-
the DFC comb lines and cw lasers (see
ad variety of applications.
page 7). The RF output signal of the DFC
MD can be counted to determine the
Three basic versions of the DFC are
frequency of the cw laser. It also enables
available: DFC CORE, DFC CORE+ and
phase or frequency stabilization of the cw
DFC SEED. The DFC CORE and its high
laser to the DFC using e.g. TOPTICA’s
performance version DFC CORE+ come
locking modules mFALC or DigiLock.
with a digital oscilloscope for beat moni-
In the DFC CORE+ version, the RF out-
toring and a GPS disciplined RF referen-
put signal can also be used to stabilize
ce included (see page 8 and 9 for more
the DFC to the cw laser which serves as
details). They both provide 4 or optionally
optical reference.
Key Features
· Patented CERO technology („zero-fCEO”)
with intrinsic CEP stability
· RMS phase stability < 35 mrad
· Frequency stability < 8·10-14 @ 1s (measured
with RF reference), or same as reference
· < 0.04 % rms power fluctuations
· One free parameter frep with up to 3 control
elements (oscillator temperature, piezo,
pump current) and > 400 kHz bandwidth
8 phase-stable outputs at 1560 nm.
Such a DFC system can be combined
Several extension modules are available
with any of TOPTICA’s tunable diode
1950 nm. It combines an outstanding
that can convert the DFC CORE/DFC
lasers to achieve a complete, frequency
passive CEP stability which challenges
CORE+ outputs to any wavelength bet-
referenced laser system including wave-
the best Ti:sapph lasers (see page 8)
ween 420 nm and 2200 nm. The exten-
length meter and counter all from one
with the convenience and robustness of
sion modules can be upgraded at any
source (see pages 10 and 11).
a fiber laser. Long-term drifts of the CEP
that are caused by a subsequent ampli-
time after purchase of the DFC CORE and
The DFC SEED unit is dedicated for OP-
fier chain can be compensated through a
CPA and high power amplifier seeding
dedicated feedback channel. The repeti-
In addition, beam combiner (DFC BC)
that require phase-stable ultrashort la-
tion rate frep of the DFC SEED can be syn-
and beat detector (DFC MD) units are
ser pulses at 1560 nm and 1030 nm or
chronized to any appropriate reference.
are interchangeable between outputs.
4
DFC Specifications
Integrated components
DFC CORE
DFC CORE+
DFC SEED
· Oscillator incl. piezo frep



· Fiber-optic amplifier and supercontinuum



· DFG unit with CERO technology



· Fiber optic pre-amplifier 1560 nm



· Lock electronics for frep



· Control computer



· 4 or optionally 8 outputs at 1560 nm


· Fiber optic amplifier and nonlinear wavelength conversion

· 2 CEP-stable outputs: 1560 nm and 1030 nm or 1950 nm + 3 optional outputs at 1560 nm

· Digital oscilloscope for beat monitoring


· RF reference: Oven-controlled quartz, GPS disciplined


· frep stabilization option to optical reference (does not include optical reference)
One free parameter frep− 3 actuators
Locking to an optical reference is achieved through feedback onto the pump cur-

rent of the oscillator. The use of an EOM
is not necessary. This keeps the oscillator
design simple and avoids piezo-electric
resonances usually present in EOMs.
Actuator
Oscillator temperature
Piezo
Pump current
Locking bandwidth
1 Hz
70 kHz
> 400 kHz
Laser outputs
DFC CORE / DFC CORE+
DFC SEED
Laser outputs
4/8 outputs @ 1560 nm (fCEO-free)
2 outputs (fCEO-free)
1560 nm each
1560 nm and 1030 nm or 1950 nm
Center wavelength
Comb spacing
80 MHz each
Bandwidth
> 20 nm each
> 60, > 25, > 150 nm
Power
> 10 mW each
> 1, > 2, > 0.6 mW (per 10 nm each)
Output coupling
Polarization maintaining fiber (FC/APC)
Spectral range covered with wavelength extensions
420 - 2200 nm
Average power @ 1560 nm with DFC IR
250 mW
Bandwidth @ 1560 nm with DFC IR
Stability (if locked to RF reference)
Bandwidth frep lock
80 nm
< 8·10-14 in 1 s, or same as reference, whichever applies first
> 70 kHz / > 400 kHz
Dimensions (H x W x D)
> 70 kHz
133 x 450 x 633 mm
Dimensions digital oscilloscope (H x W x D)
40 x 190 x 170 mm
n.a.
Dimensions quartz, GPS reference (H x W x D)
60 x 100 x 165 mm, 58 x 170 x 140 mm
n.a.
Weight
Power supply
< 30 kg
100...120 V / 220...240 VAC, 50...60 Hz (auto detect)
5
Modular Extensions
Extensions: 420 - 2200 nm
Various extension modules are available
that convert the offset-free fundamental
output of the DFC CORE from 1560 nm
to any desired wavelength between
420 nm and 2200 nm. The wavelength
conversion in these modules is achieved
Extension module
with the well-established technology
of TOPTICA’s ultrafast fiber lasers. All
extension modules use highly stable
all-fiber amplification, nonlinear conversion and compression. The output power
of all extension modules allows for phase-
locking of cw lasers. Special wavelength
extensions are available on request or
included in TOPTICA’s complete stabilized laser systems (page 10).
Wavelength range
Bandwidth (FWHM)
DFC IR
1560 nm
80 nm (> 250 mW)
DFC NIR
780 nm
10 nm
DFC SCVIS
530 - 900 nm
370 nm
DFC SCIR
980 - 2200 nm
1220 nm
DFC DVIS*
420 - 840 nm
~ 2 nm
DFC SCNIR
840 - 900 nm
~ 10 nm wide
Other custom wavelengths upon request.
*The Designed VISible (DVIS) extension delivers highest output power in a narrow bandwidth at a user defined wavelength.
This extension is to be preferred over DFC SCVIS if broad output is not required.
Example: Complete laser system for 40Ca+ spectroscopy
794 nm*
Amp
Piezo
Er3+Amp
I Pump
Temp
Er3+ Fiber
Oscillator
Super
Continuum
HNLF
Difference
Frequency
Generation
SHG
DFC NIR
Er3+Amp
DFC BC DFC MD
DLC TA SHG pro 397 nm
PhaseLock
mFALC
866 nm
DFG Unit
Amp
HNLF
DFC SCNIR
DFC BC DFC MD
DLC DL pro 866 nm
PhaseLock
mFALC
1560 nm
frep stab. unit
Amp
DFC IR
729 nm
RF Reference
Amp
DFC-CORE+
HNLF
SHG
DFC DVIS
DFC BC DFC MD
DLC TA pro 729 nm
Fast
Lock
FALC
HF Cavity
iBeam smart 375 nm
DLC DLpro 423 nm
Wavemeter
* special DFC NIR configuration
6
Beat Detection
TOPTICA’s beat detection consists of
two flexible modules: DFC BC and DFC
MD. Separating beam combination and
beat detection into two units allows for
placing them at different locations. This
increases the flexibility when minimizing
loop delays in the laboratory. Both units
are as versatile as possible and machined out of one block. Only high quality
optics and mechanics are used for a reliable operation. The DFC BC and DFC
MD units are specifically designed for a
combination of the DFC with TOPTICA’s
DL pro tunable diode laser series but can
also be used with other cw lasers.
DFC BC
The DFC BC (beam combiner) spatially
overlaps the DFC output with a cw la-
ser. The relative intensities between both
beams can be adjusted internally. If a
fixed splitting ratio is acceptable the DFC
BC can be replaced by an all-fiber combiner. The unit can also be used individually as an ultra-stable combiner and fiber
coupler for any pair of laser beams.
the RF beat-note signal. It enables three
different operation modes:
· Measurement of the beat frequency
using the beat monitoring unit of
the DFC CORE module
· Active locking of the cw laser to the
DFC (requires additional locking
electronics for the cw laser)
· Locking of the DFC to the cw laser
(requires DFC CORE+ version)
DFC MD
The DFC MD (monochromatic detector)
detects a beat-note between the DFC
and a cw laser with the highest possible
signal to noise ratio. Using a grating-based adjustable filter with a bandwidth of
10 GHz and a tuning range of several
10 nm, it filters a narrow spectral component of the combined cw laser and
DFC. The unit also includes a low-noise
photodetector and amplifier to detect
DFC MD
The photodetector can be detached
from the DFC MD unit to convert it into a
monochromator serving as narrow band
frequency filter. The output of the monochromator can be fiber-coupled or attached with slits of different sizes defining
the filtering bandwidth.
DFC BC
cw laser input
(fiber-coupled)
RF beat-note
output
Comb input
(fiber-coupled)
cw laser output (free space,
fiber-coupled, optional)
DFC BC
DFC MD
Inputs
1. Frequency comb: Fiber-coupled (FC/APC fiber coupler
included), > 0.25 mW/nm recommended
2. cw laser > 100 μW recommended, 1 mW ideal
(fiber-coupled, fiber coupler included)
Frequency comb + cw laser: Fiber-coupled
(fiber coupler included)
Outputs
1. Frequency comb + cw laser: Fiber-coupled
(fiber coupler and SM/PM fiber included)
2. cw laser: Free beam (fiber coupling optional)
RF signal, amplified for use with mFALC
Wavelength
Spectral width of
operating range
Filter element
420 nm - 2200 nm
approx. 50 nm (depends on central wavelength)
50 nm (depends on central wavelength)
n.a.
10 GHz bandwidth grating (other bandwidths on request)
Optical resolution > 50.000
Tuning via manual adjustment of µm-screw incl. scale reading
Tuning resolution < 1 GHz (typ.)
Dimensions (H x W x D) 49 x 100 x 100 mm
64 x 60 x 120 mm
7
DFC Characteristics
Spectral interferometry
The performance of the CERO technology
is best characterized by means of spectral interferometry. The dedicated setup
consists of an f-2f interferometer with
optical spectrum analyzer which records
optical fringes at the output. It measures
the absolute out-of-loop phase stability
of the fCEO cancelation. The figure below
shows a spectrogram of the interferen-
ce fringes recorded over a time of 20 s.
The high interference contrast is stable
over the full time span and no offset phase drift is observed. The measurement
shows an rms phase stability of 8 mrad
over 20 s, which is limited by the stability
of the out-of-loop optical f-2f interferometer. The real phase stability of the DFC
is expected to be below this value.
Spectral interferometry with DFC
· 98 % fringe contrast
· < 8 mrad rms phase stability in 20 s
@ [50 mHz, 5 Hz]
· Out of loop measurement
· Limited by measurement setup
1095
1090
Wavelength (nm)
1085
1080
1075
1070
1065
Phase (mrad)
1060
50
25
0
-25
-50
0
5
RF reference
The DFC CORE modules include an
RF reference to stabilize the repetition rate frep of the frequency comb. It
consists of a low phase-noise 80 MHz
reference (oven-controlled quartz). For
improved long-term stability this quartz
is disciplined to a GPS module operating
at 10 MHz. To optimize the stability of
the DFC repetition rate, the 10th harmonic
of frep (80 MHz) is referenced to the 10th
harmonic of the RF reference at 800 MHz
in the frep locking circuit.
10-6
10-5
10-7
10-7
10-8
10-9
module, better RF references available
on request)
10-13
40,000 s
4 · 10-13
10,000 s
2.4 · 10-12
1,000 s
4 · 10
from 400 s to 10 s
-12
1s
10-10
10-11
10-13
10-12
101
102
103
104
105
Fourier Frequency (Hz)
8
20
Typical stability values (standard GPS
1.3 · 10-12
10-9
10-11
10-15
100
15
σy (t)
Sφ (dBc/Hz)
10
Time (s)
106
107
10-13 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5
10 10 10 10 10 10 10 10 10 10 10 10 10
Time (s)
Phase-noise referred to 800 MHz (left) and
Allan deviation (right) of the 80 MHz reference
(red) and the 10 MHz GPS module (blue).
Crossover is at typ. 10 Hz.
Beat Monitoring Unit
The DFC CORE/DFC CORE+ includes a
beat monitoring unit that can display the
beat-note between the DFC and a cw
laser. The beat-note can be generated
easily using the DFC BC and DFC MD
modules. The beat monitoring unit includes a 200 MHz four-channel digital oscilloscope with spectrum analyzer function.
The unit can display up to four beat-notes
simultaneously. Detailed specifications
and additional functions of the digital
oscilloscope are listed below.
-21.0
-32.0
RF power (dB)
-43.0
-54.0
-65.0
-76.0
-87.0
-98.0
-109.0
-120.0
46.0
47.0
48.0
49.0
Frequency (MHz)
In-loop phase-lock beat-note between
the DFC-system and a 729 nm cw laser
with Hz-level linewidth detected with DFC
BC and DFC MD and displayed with the
beat monitoring unit.
Specifications digital oscilloscope
VERTICAL
Number of channels
4
Bandwidth (-3 dB)
8 to 15-bit modes: 200 MHz , 16-bit mode: 60 MHz
Rise time (calculated, 10% to 90%)
8 to 15-bit modes: 1.8 ns, 16-bit mode: 5.8 ns
Input connectors
BNCs on front panel, 1 MΩ ±1 % || 13 pF, ±1 pF
Input coupling and sensitivity
AC/DC, 2 mV/div to 4 V/div
Input ranges
±10 mV to ± 20 V full scale, in 11 ranges
HORIZONTAL
Max. sampling rate 1 channel 16-bit mode 62.5 MS/s
Max. sampling rate 1 channel 8-bit mode
1 GS/s
Max. sampling rate 4 channels 8-bit mode 250 MS/s
Timebase ranges
500 ps/div to 1000 s/div
Buffer memory (8 bit / ≥ 12-bit)
512 MS / 256 MS
Buffer memory continous streaming
256 MS
SPECTRUM ANALYZER
Frequency range
DC to 200 MHz
FUNCTION GENERATOR
ARBITRARY WAVEFORM GENERATOR (AWG)
GENERAL
Dimensions (H x W x D)
40 x 190 x 170 mm (including connectors)
Weight
< 0.5 kg
9
Australia & New Zealand
Lastek Pty. Ltd.
Thebarton Campus
10 Reid Street
5031 Thebarton, SA, Australia
Phone: +61 8 8443 8668
Fax:
+61 8 8443 8427
sales@lastek.com.au
www.lastek.com.au
Japan
China
Universal Technology Co. Ltd.
NanXinCang Business Tower, A1505
No. 22 DongSiShiTiao
Beijing 100007, P.R. China
Phone: +86 10-516 90 388-500
Fax:
+86-10-516 90 100
oe@universaltechco.cn
www.universaltechco.com
Korea
JINSUNG INSTRUMENTS, INC.
5F, A-Dong, Leaders Town
#306, ManNyeon-Dong, Seo-Gu
Daejeon, 302-834, South Korea
Phone: +82 42 823 5300
Fax:
+82 42 823 7447
sales@jinsunglaser.com
www.jinsunginst.com
France
Opton Laser International
Parc Club Orsay Université
29, rue Jean Rostand
F-91893 Orsay Cedex, France
Phone: +33 1 6941 0405
Fax:
+33 1 6941 3290
ventes@optonlaser.com
www.optonlaser.com
Russia
EuroLase Ltd.
Profsoyuznaya 93-A
Office 404
117997 Moscow, Russia
Phone: +7 495 3363044
Fax:
+7 495 3363044
eurolase@eurolase.ru
www.eurolase.ru
United Kingdom & Ireland
TOPTICA Photonics UK
Unit SU4B, Lansbury Estate
102 Lower Guildford Road
Knaphill, Woking
Surrey, GU21 2EP, Great Britain
Phone: +44 1483 799 030
Fax:
+44 1483 799 076
enquiries@toptica-uk.com
www.toptica.com
India
Simco Global Technology &
Systems Ltd.
Simco House (Head Office)
14 Bhawani Kunj
Behind Sector D-II Vasant Kunj
110070 New Delhi, India
Phone: +91 11 2689 9867
Fax:
+91 11 2612 4461
simco.del@simcogroup.in
www.simco-groups.com
Singapore / Malaysia
Precision Technologies Pte Ltd
211 Henderson Road # 13-02
Henderson Industrial Park
Singapore 159552
Phone: +65 6273 4573
Fax:
+65 6273 8898
precision@pretech.com.sg
www.pretech.com.sg
USA, Canada & Mexico
TOPTICA Photonics, Inc.
1286 Blossom Drive
Victor / Rochester, NY 14564, U.S.A.
Phone: +1 585 657 6663
Fax:
+1 877 277 9897
sales@toptica-usa.com
www.toptica.com
Israel
Lahat Technologies Ltd.
17 Atir Yeda St.
Kfar Saba 4464313, Israel
Phone: +972 9 76 46 200
Fax:
+972 9 76 46 204
sales@lahat.co.il
www.lahat.co.il
Spain
Delta Optics
Edificio CTM O-210
Crta Villaverde-Vallecas, Km 3,500
28053 Madrid, Spain
Phone: +34 911 130 824
Fax:
+34 910 113 757
info@deltaoptics.es
www.deltaoptics.es
Every other country not listed
TOPTICA Photonics AG
Lochhamer Schlag 19
D-82166 Graefelfing / Munich,
Germany
Phone: +49 89 85837 0
Fax:
+49 89 85837 200
sales@toptica.com
www.toptica.com
TOPTICA Photonics AG
Lochhamer Schlag 19
D-82166 Graefelfing / Munich
Germany
Phone: +49 89 85837-0
Fax:
+49 89 85837-200
sales@toptica.com
www.toptica.com
TOPTICA Photonics, Inc.
1286 Blossom Drive
Victor / Rochester, NY 14564
U.S.A.
Phone: +1 585 657 6663
Fax:
+1 877 277 9897
sales@toptica-usa.com
www.toptica.com
TOPTICA Photonics, K.K.
2-9-5, Miyanishi-cho, Fuchu-shi,
Tokyo, 183-0022
Japan
Phone:+81 42 306 9906
Fax: +81 42 306 9907
sales@toptica.com
www.toptica.com
TOPTICA PHOTONICS, K.K.
2-9-5, Miyanishi-cho, Fuchu-shi, Tokyo,
183-0022, Japan
Phone: +81 42 306 9906
Fax:
+81 42 306 9907
sales@toptica.com
www.toptica.com
Taiwan
SLEO Photonics Co. Ltd.
6F, No. 2, Lane 74
An-der Street
Hsintien Area, New Taipei City
23154 Taiwan
Phone: +886 2 2211 5418
Fax:
+886 2 2211 5401
sleo.jimmy@msa.hinet.net
www.sleophotonics.com
Luxton Inc.
F4, No. 2, Technology Road V,
Hsinchu Science Park,
Hsinchu 30078, Taiwan
Phone: +886 3 666 2097
Fax:
+886 3 666 2124
service@luxton.com.tw
www.luxton.com.tw
BR-141-64A-DFC 2016-08
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