How to use square camera on swift - ios

Question

When I use ios system camera, I can select the square camera type. I want to implement this on swift, but how can I do that? Below is the code I use for camera. The initialSession() is used to create the AVCaptureSession object. setUpCameraLayer() method is to show the camera on the view. How can I use square camera on below code?
func initialSession(){
self.session = AVCaptureSession()
do {
try self.videoInput = AVCaptureDeviceInput(device: self.backCamera())
} catch {
}
self.stillImageOutput = AVCaptureStillImageOutput()
self.stillImageOutput?.outputSettings = [AVVideoCodecKey:AVVideoCodecJPEG]
if self.session!.canAddInput(self.videoInput){
self.session?.addInput(self.videoInput)
}
if self.session!.canAddOutput(self.stillImageOutput){
self.session?.addOutput(self.stillImageOutput)
}
}
func setUpCameraLayer(){
if self.previewLayer == nil {
self.previewLayer = AVCaptureVideoPreviewLayer(session: self.session)
self.backView.frame = CGRectMake(0, 0, self.view.bounds.width,self.view.bounds.width)
let view:UIView = self.backView
let viewLayer:CALayer = view.layer
viewLayer.masksToBounds = true
let bounds:CGRect = view.bounds
self.previewLayer?.frame = bounds
self.previewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill//AVLayerVideoGravityResizeAspect
//viewLayer.insertSublayer(self.previewLayer!.below: viewLayer.sublayers![0])
view.layer.addSublayer(self.previewLayer!)
self.picture.frame = self.backView.frame
self.backView.addSubview(self.picture)
self.picture.hidden = true
}
}