ALMA CLOA Improvements and Upgrades...16 ALMA Future Science Development Workshop, 24-25 Aug 2016 To realize the ALMA 2030 vision… • As delivered, the CLOA is a complete, “holistically”

1 ALMA Future Science Development Workshop, 24-25 Aug 2016

ALMA CLOA Improvements and Upgrades

Christophe Jacques, Bill Shillue, Jason Castro Photonic LO Group


Outline

•  Overview of current system performance •  ALMA 2030 motivation •  Phase Drift, Visibility and Coherence •  Longer Baselines •  CLOA 2.0


Current Central LO References for ALMA

AOS Central Bldg

Key

Antenna

Central Reference Generator

Correlator

Master Laser and Laser

Synthesizer

Master Frequency Standard

LO Photonic Receiver

LO Reference ReceiverCentral

Variable Reference

Line Length

Corrector

10 MHz

125 MHz

13.5—20 GHz

WDM1556 nm27-122

GHz

1532 nm, 2 GHz, 125 MHz, 48 msec

5 MHz

WDM

Buried Fiber to Antenna

48 msec

1st LO Offset

20-45 MHz 1st LO PLL ref

2nd LO ref 8-14 GHz comb2nd, 3rd LO 125 MHz

1st LO ref 27-122 GHz

`

Fiber Patch Panel

ElectronicFiber Optic

5 MHz


Current Central LO References for ALMA - 2 •  Tunable LO for all ALMA bands, 27~ 122 GHz, including an

extended Band 1 tuning range of 27~ 39 GHz •  1st LO RMS integrated phase noise < 53 fs •  1st LO phase drift < 18 fs, over 15 km (w/. active stabilization). •  < 1 second fast-switching time to any frequency •  5 independently tunable SubArrays, expandable to 6 •  For all 66 antennas, can already expand to 80 •  1 hour reset free operation / 24 hour polarization calibration

stability

1E-15

1E-14

1E-13

1E-12

1E-11

10 100 1000

Pha

se S

truc

ture

Fun

ctio

n (s

ec)

Tau (Seconds)

Measured PhaseExpected Phase without CorrectionLO spec ALMA LO Phase

Drift over 300 seconds


Current Central LO References for ALMA - 3 •  Antenna motion, a 100+ ton structure:

–  Azimuth: -275 to + 275 degrees –  Elevation: -1.5 to 93.5 degrees –  Velocity: 6 deg/sec –  Acceleration: 18 deg/sec2

Unprecedented phase stability at each antenna guaranteed vs. temperature, time, fiber length, antenna motion, …


Current Central LO References for ALMA - 4


ALMA 2030 motivation - 1

To enhance current ALMA Science, and allow new study fields: •  Galactic and Extra-Galactic astronomy, galactic surveys, Solar

Science, mapping, innermost cores of protoplanetary disks, imaging of masers in excited regions, imaging of nearby star-forming disks and star-forming galaxies, astrometry of nearby solar-type stars, …

•  Imaging and molecular spectroscopy of small feature size solar system objects (~10km at 10 AU): planetary moons, Kuiper Belt objects.

We need improvements in array sensitivity,

resolution, FOV, image quality, and calibration.


ALMA 2030 motivation - 2 •  The existing hardware was not designed to support these science

enhancements. It was “delicately crafted” to meet the original specifications.

•  We should pro-actively identify and study which areas of the CLOA will require upgrading, and how.

•  …and since the CLOA must operate well past 2030, reliability of these solutions has to be on par with current system.


Not only to realize the ALMA 2030 vision…

•  The current ALMA array would quickly benefit from these potential improvements in coherence, phase and calibration stability.

Photonic LOV 1.0

Line Length CorrectionV. 1.0

15 km

Currrent implementation

Photonic LOV 2.0


n1 km

BidirectionalOptical amplifier

n2 km LO Regeneration n3 km

Study implementation


Phase Drift, Visibility and Coherence •  Current 1st LO overall phase noise measured (mm-wave antenna based LO

locked to Laser Synthesizer): < 53 fs for 65~122 GHz •  Laser Synthesizer PLL corrects phase noise to ~ 0.01 rad (< 27 fs)

During the best months of the year, the quietest time of the day, and the highest observing bands 8/9/10, is the phase noise & slow phase drift limiting the

instrument, i.e. degrading array visibility ?

(temporal delay/phase noise drift variations be smaller than those of the natural environment at least 95% of the time, over 300 s)


Phase Drift, Visibility and Coherence study What are the areas of potential improvement ? •  Improve the phase stability of the LS by 10 %, to regain maximum

value at highest frequencies (coherence, resolution) •  Reduce the LS locking time to enable more frequent LO tunings

(efficiency) •  Improve band-switching/phase calibration, to reduce/eliminate LS

lock failures •  Improve antenna-to-antenna phase stability: Line Length

Corrector (bigger impact at shorter wavelengths) •  Increase the dynamic range of the active phase correction

system, increasing time between calibrations (efficiency) •  Increase Band 1 CLOA tuning range past 39 GHz


Longer Baselines - 1

•  Multiple sources (ALMA Development Working Group, 2008, A Roadmap for Developing ALMA, Kameno-san’s presentation, 2013…) conclude that longer baselines (20, 30, 50, …300 km) would allow for improved Galactic, Extra-Galactic science (better resolution, more precise imaging, more accurate astrometry)

Ex: a 32 km baseline (~double the current one) would allow an ~ 8 mas resolution @ 230 GHz – think of the HL Tau & SDP81 gravitational lens studies, achieved at 10 km

But … (in addition to trenching & data transport, pad and antenna costs,

snow removal and maintenance)


Longer Baselines -2: Master Laser Coherence

X

> 50 % at 30 km

•  Reliable lock achieved at 22.5 km at the NTC (lab environment) •  Fringes observed @ 86.2 GHz between an AOS and an OSF antenna, 24 km

baseline (Olguin et al. 2012)

This is just about the maximum that can be achieved with the current Master Laser


Longer Baselines study

•  We need to find a laser with much greater coherence -OR- implement a new correction/regeneration scheme

•  The Line Length Correction needs a greater range (currently 4.5 mm) to be able to correct the much longer path lengths

•  We should look at alternative technologies to stretching fiber, to achieve greater range and speed, less polarization sensitivity (because of polarization to phase conversion)

Less than 0.4 radians SOP change for 540-‐degree antenna rota9on.

SOP change plo<ed against input

polariza9on


Longer Baselines study

•  The Line Length Correction needs greater resolution in the fringe detector circuit, to 16 bits, to implement a finer fringe count and ultimately allow a “software only” type correction. A 50 km baseline may require it.

•  Direct photonic LO for the longer baseline antennas ? Maybe a hybrid system ?

We propose to provide a roadmap for the technical solutions that need to be implemented before longer

baselines are decided upon.


To realize the ALMA 2030 vision…

•  As delivered, the CLOA is a complete, “holistically” designed system, where each element impacts phase stability, power budget, polarization change … of the entire LO.

•  Increasing the baseline length is NON trivial. •  The team, having delivered the current state-of-the-art LO, is

“wired” to look for solutions that will integrate into the existing ALMA structure, at the lowest cost.

Photonic LOV 1.0


15 km

Currrent implementation

Photonic LOV 2.0


n1 km

BidirectionalOptical amplifier

n2 km LO Regeneration n3 km

Study implementation


Photonic LO group has a complete CLOA at the NTC 1 x MFS, CRG, CVR, ML, LS, MLD, PRD, LFRD 2 x SAS, LLC, LPR, FOW, WCA, and approx. 75 km of fiber


“Proof-of-Concept” bidirectional EDFA

Er doped fiber

bandpass filter

LO Signal Output

Monintor

pump/signal combiner

980 nmpump laser

5/95

Return Signal Input

Monitor

LO Signal Input

Monitor

Return Signal Output

Monintor

LO Signal (to antenna) Return Signal (from Antenna)

5/95

Allows stable LLC locking to the “equivalent” of a 70 km baseline.


www.nrao.edu science.nrao.edu public.nrao.edu

The National Radio Astronomy Observatory is a facility of the National Science Foundation

operated under cooperative agreement by Associated Universities, Inc.


Current Central LO for ALMA


Elevation wrap

Azimuth wrap

Buried Fiber Optic Cable,

L<15 km

Photonic Distribution

Master Laser

4 sets of 66 Fibers

Subarray Switch

Modules

Line Length Corrector Modules

LaserSynthesizers

ML ref

1 Set of 66 Fibers


WCA

WCAFRM

WCA

Band 1

Band 2

Band 9

WCABand 10

FrequencyReferences

To other Antennas

Master Laser (1556 nm)Master + Slave (1556 + 1557 nm)Electronic Signal


Subarray Switch Line Length Corrector


FRM

Band 1

Band 10

Frequency Shifter

EDFA 1:10 Switch

Compensating Fiber

LO RCVR

LO1st LO DriverYIG+Active

Multiplier Chain and PLL

Input from Laser Synthesizers

Div by N

Phase DetectorFringe CounterStretcher DriverMicroControlller

50 MHz

Fiber Stretcher Polarimeter

5 MHz ref

PBS1:6

Switch

PC

PC

“Beatnote” Det

5% PC

l sl M

FBG

WDM

1532 nm

LO Reference Receiver

WDM

48 msec

1st LO Offset

20-45 MHz 1st LO PLL ref

2nd LO ref 8-14 GHz comb2nd, 3rd LO 125 MHz

Compensating Fiber

Round-‐trip phase correc9on path in red

Documents

ALMA CLOA Improvements and Upgrades...16 ALMA Future Science Development Workshop, 24-25 Aug 2016 To realize the ALMA 2030 vision… • As delivered, the CLOA is a complete, “holistically”