(david crampton, kei szeto, paolo spano, zhongwen hu, chao …€¦ · (david crampton, kei szeto,...

Multiplexing solutions

Shan Mignot & Rick Murowinski

on behalf of the multiplexing task force(David Crampton, Kei Szeto, Paolo Spano, Zhongwen Hu, Chao Zhai, Derrick Salmon, Alan McConnachie, Nicolas Flagey, Weimin Sun, Will Saunders, Peter Gillingham)

Waikoloa, Hawaii, 29/07/2015

Multiplexing trade study

Multiplexing solutions ― Waikoloa, Hawaii, 29/07/2015 ― Shan Mignot 2

Purpose


Multiplexing issue


3468 Robot Fiber Positioner

High ResolutionSpectrographs (2)

Low/Mid Resolution Spectrographs (4)

Low/Mid Resolution Fibre Bundle

High Resolution Fibre Bundle

• Design the fiber optics network• Identify solutions for

• light collection

• light transmission

• light distribution

• Evaluate combinations• large number of combinations

(works as a Cartesian product)

• Restrict the design space for concept studies

Cartesian product


• dedicated fibres• 1:1 HR & LR• 1:3 HR & LR

• shared HR/LR fibres

• fibre slicing

• 1-4 photonic lantern

Echidna

ϕ-θ

β-ϕ-θ

• fixed fibres

• optical switches

• moving slit

• optical relay

• fibre reconfiguration

× ×

• Plug plates & pick’n’place technologies dismissed• operations cost

• short reconfiguration

• large number of fibres

• calibration (repeatability)

• high TRL required• MSE is risk averse

• fast project development

→ fibre slicing & photonic lantern abandoned

Strategy


Combinations


Collection Transmission Distribution

Echidna 3200 3200 fibres moving slit

Echidna 3200 3200 fibres optical relay

Echidna 3200 3200 fibres optical switch (3200+800)

Echidna 3200 3200 LR + 800 HR 800 positioners with 2 fibres

ϕ-θ 3200 3200 fibres moving slit

ϕ-θ 3200 3200 fibres optical relay

ϕ-θ 3200 3200 fibres optical switch (3200+800)

ϕ-θ 3200 3200 LR + 800 HR 800 positioners with 2 fibres

ϕ-θ 3200 3200 LR + 3200 HR 3200 positioners with 2 fibres

β-ϕ-θ 800 3200 fibres moving slit

β-ϕ-θ 800 3200 LR + 800 HR 800 positioners with 2 fibres

• Performance• throughput• positioning accuracy• FRD• reconfiguration delay• target allocation yield LR / HR

• Project management• cost• TRL• simplicity• risks (performance, cost, delay)

• Reliability• mean time between failures• mean time to repair

• Usage• remotely reconfigurable

Trade-off: evaluation criteria


• Interfaces• mass• dimensions• cable wrap• slit assemblies• slit exchange

• Calibration• sky subtraction• wavelength• spectrophotometry

• Miscellaneous• simultaneous LR & HR• upgrade without interruption

of operations• compatible with IR

Trade-off: decision matrix


• Manufacturing advantage in placing 3468 positioners in a hexagonal pattern

• Dedicated HR / LR fibres• allows for placing LR spectrographs on the Nasmyth platforms to reduce fibre

length (for UV transmission)

• Tie between Echidna & ϕ-θ technologies (risk, performance, cost)

• Preferred combinations• 3468 Echidna, 3468 LR + 1156 HR fibres (1156 positioners carry two fibres)→ Echidna allows full fill factor for HR due to patrol region

• 3468 ϕ-θ, 3468 LR + 1156 HR fibres (1156 positioners carry two fibres)→ Incomplete fill factor balanced by cost saving versus having 3468 HR fibres: 4 HR spectrographs!

• The 3468 ϕ-θ, 3468 LR + 3468 HR fibres scored nearly as well but will adversely impact HR spectrograph cost unless we have an optical switch.

Outcome (I)


• Concept studies• 3468 Echidna (2 fibres per positioner)• 3468 ϕ-θ (2 fibres per positioner)• LR spectrograph (2 parallel studies)• HR spectrograph (2 parallel studies)• optical switch

• achieve full HR fill factor with ϕ-θ• assess flexibility gain• performance & risk• design to reduce 3468 to 1156 HR fibres

• fibre train system• LR spectrograph on telescope Az structure• HR spectrograph in Coudé room• study of connectors• installation/removal procedures

Outcome (II)


Discussion


• Simultaneous LR & HR observations

• Dedicated fibres• different LR/HR core diameters• Possibility of OH suppression fibres

• Performance• inter-spectra contamination• HR target allocation yield / number of spectrographs• fibre repositioning (open loop / closed loop)

• Target allocation• minimum distance between fibres• contamination (multiple stars in fibre)• complete observation of field of view• clustering of fibres• compatibility with IFUs

• Calibration• repeatability of transmission (sky subtraction and spectrophotometry)• repeatability of spectrograph illumination (both near field and far field)• opportunity for simultaneous wavelength calibration (optical switches)

Open questions


(david crampton, kei szeto, paolo spano, zhongwen hu, chao …€¦ · (david crampton, kei szeto,...

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