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measurements of the cosmic microwave background ( cmb ) temperature anisotropy successfully constrained many cosmological parameters .. the cmb is also weakly linearly polarized .
the cmb polarization could give tighter constrains on cosmological parameters and open windows for studying fundamental physics .
measurements of even parity polarization pattern , e - mode , of the cmb agree with temperature anisotropy measurements @xcite .
recently , initial measurements of the odd parity polarization pattern , b - mode , of the cmb were also reported . @xcite .
the b - mode polarization has two primary sources .
primordial gravitational waves , if present , would polarize the cmb at degree angular scale @xcite .
tighter upper limits or detection of the primordial b - mode signal will put constraints on the inflation model and energy level of the inflation potential .
weak gravitational lensing from large scale structures distorts the e - mode pattern to produce small amounts of b - mode polarization pattern @xcite . the b - mode signal from weak gravitational lensing peak around ten arcmin angular scales .
characterization of gravitationally lensed b - mode signal could constrain parameters such as the sum of neutrino masses , evolution of the dark energy equation of state , primordial magnetic fields and cosmic birefringence .
precise characterization of the gravitational lensing b - mode will be important to decouple the lensing signal from the primordial inflationary signal .
planck s report on the cmb foregrounds suggests that polarized foregrounds such as synchrotron radiation and dust emission need to be carefully subtracted for accurate cmb polarization measurements @xcite .
the polarbear-2 receiver is a highly sensitive receiver with broad frequency coverage for foreground mitigation .
the polarbear-2 receiver will observe from the james ax observatory at 5,200 meter altitude in the chilean atacama desert .
the site has access to @xmath5 of the sky .
this allows cross - correlation with other experiments .
the polarbear-2 receiver will be mounted on a telescope with same design as the huan tran telescope ( htt ) that is currently observing with the polarbear-1 receiver .
the htt features an offset gregorian design obeying the mizuguchi - dragone condition to minimize instrumental cross - polarization .
the htt has co - moving baffles to minimize sidelobes .
3.5 meter primary mirror produces a 3.5-arcmin ( 5.2-arcmin ) fwhm beam at 150  ghz ( 95  ghz ) .
the polarbear-2 receiver will have instantaneous array sensitivity of 5.8  @xmath0k@xmath1 in each frequency band .
the simons array is a project to further increase sensitivity by deploying three polarbear-2 type receivers including the polarbear-2 receiver .
the first receiver will deploy at 95  ghz and 150  ghz frequencies in 2016 .
the second receiver will cover 95  ghz and 150  ghz , and the third receiver will cover 150  ghz and 220  ghz bands .
the second and third receivers will deploy in 2017 .
sensitivity of the simons array in its final configuration is 4.1  @xmath0k@xmath1 in the 95  ghz band , 3.4  @xmath0k@xmath1 in the 150  ghz band and 11.5  @xmath0k@xmath1 in the 220  ghz band .
the simons array will be able to constrain the tensor - to - scalar ratio @xmath6 to @xmath7 when considering statistical noise alone , and @xmath2 at @xmath3 when foregrounds are cleaned @xcite .
the simons array will also be able to constrain the sum of neutrino masses to 19 mev ( @xmath8 ) when considering statistical noise alone , and 40 mev ( @xmath8 ) when foreground effect is considered with foreground cleaning by cross - correlation with spectroscopic galaxy surveys .
pitch ( bottom right ) .
the sinusoidal circular structure is a broadband antenna .
large rectangular structures are tes bolometers . the rf diplexer filter is visible between the antenna and the bolometers ( bottom right).,width=604 ]    a cross - sectional view of the polarbear-2 receiver is shown in figure  [ fig : pb2combined ] .
two cryomech pt415 pulse - tube coolers provide cooling power to the receiver . annealed 6-n aluminum strips are epoxied to receiver shells to increase thermal conductivity of the receiver .
a chase cryogenics three - stage helium sorption refrigerator provide the focal plane tower with 2  kelvin , 350  milli - kelvin and 270  milli - kelvin stages .
+ three reimaging lenses and an infrared filter are fabricated from nihon ceratec s @xmath9 purity alumina .
the high optical index of alumina ( @xmath10 ) minimizes abberation in optics .
the alumina has low loss - tangent ( @xmath11 ) , and this keeps receiver efficiency high .
high thermal conductivity of the alumina helps with overall cryogenic performance @xcite .
alumina lenses are anti - reflection coated with two - layer epoxy coating , thermal sprayed ceramic coating and expanded kapton coating @xcite .
the optical design achieves a strehl ratio greater than 0.90 over entire 365 mm diameter focal plane .
the field of view of the polarbear-2 instrument is @xmath12 .
optical efficiency of the entire system is 24% at 95  ghz and 31  % at 150  ghz .
+ the focal plane is shown in figure  [ fig : pb2combined ] . a 365  mm diameter focal plane tower houses seven detector array modules .
each module has 271 dual linear polarized pixels that simultaneously detect cmb radiation in the 95  ghz and 150  ghz bands .
each pixel has a silicon lens coupled broadband sinuous antenna that couples optical signal onto a rf circuit on a wafer .
bandpass filters on the wafer split the signal into two separate bands , then transition edge sensor ( tes ) bolometers detects the signal @xcite .
silicon lenslet array is anti - reflection coated with two layers of epoxy based coating @xcite .
readout electronics are assembled behind the detector array for a modular design .
+ tes bolometers are read - out by frequency multiplexed superconducting quantum interference device ( squid ) amplifiers @xcite .
forty channels are frequency multiplexed between 1.6 mhz to 4.2 mhz with logarithmically increasing frequency spacing .
digital active nulling technology corrects for phase delay and reduces parasitic inductance from circuit elements between the bias resistor and the squid @xcite .
superconducting resonators for frequency multiplexing are lithographed on silicon wafers for low loss , high frequency precision and kilo - channel scalability @xcite .
we developed superconducting niobium - titanium parallel plate transmission lines for wiring between the milli - kelvin and 4-kelvin stages .
the low thermal conductivity of niobium - titanium provides thermal isolation , while the high width - to - height ratio of the parallel plate transmission line provides low inductance per length ( @xmath13 ) that allows stiff voltage biases of tes bolometers .
the polarbear-2 and the simons array experiment will measure polarization of the cmb with high sensitivity . the polarbear-2 will deploy in 2016 , and the simons array will fully deploy in 2017 .
we acknowledge support from the mext kahenhi grant 21111002 , nsf grant ast-0618398 , nasa grant nng06gj08 g , the simons foundation , natural sciences and engineering research council , canadian institute for advanced research , japan society for the promotion of science , and the conicyt provided invaluable funding and support .
detectors were fabricated at the berkeley marvell nanofabrication laboratory .
we present an overview of the design and status of the polarbear-2 and the simons array experiments . 
 polarbear-2 is a cosmic microwave background polarimetry experiment which aims to characterize the arc - minute angular scale b - mode signal from weak gravitational lensing and search for the degree angular scale b - mode signal from inflationary gravitational waves . 
 the receiver has a 365  mm diameter focal plane cooled to 270  milli - kelvin . 
 the focal plane is filled with 7,588 dichroic lenslet - antenna coupled polarization sensitive transition edge sensor ( tes ) bolometric pixels that are sensitive to 95  ghz and 150  ghz bands simultaneously . 
 the tes bolometers are read - out by squids with 40 channel frequency domain multiplexing . 
 refractive optical elements are made with high purity alumina to achieve high optical throughput . 
 the receiver is designed to achieve noise equivalent temperature of 5.8  @xmath0k@xmath1 in each frequency band . 
 polarbear-2 will deploy in 2016 in the atacama desert in chile . 
 the simons array is a project to further increase sensitivity by deploying three polarbear-2 type receivers 
 . the simons array will cover 95  ghz , 150  ghz and 220  ghz frequency bands for foreground control . 
 the simons array will be able to constrain tensor - to - scalar ratio and sum of neutrino masses to @xmath2 at @xmath3 and @xmath4 to 40 mev .