[1] Cakmakci O, Rolland J. Head-worn displays: a review[J]. Journal of Display Technology, 2, 199-216(2006). http://ieeexplore.ieee.org/document/1677544/

[2] Okuyama A, Yamazaki S. Optical system, image observing apparatus. -01-06[P]. image pickup apparatus using it: US5706136.(1998).

[4] Ye J F, Chen L, Li X H et al. Review of optical freeform surface representation technique and its application[J]. Optical Engineering, 56, 110901(2017). http://spie.org/Publications/Journal/10.1117/1.OE.56.11.110901

[5] Cakmakci O, Rolland J. Design and fabrication of a dual-element off-axis near-eye optical magnifier[J]. Optics Letters, 32, 1363-1365(2007). http://www.opticsinfobase.org/abstract.cfm?URI=ol-32-11-1363

[6] Cakmakci O, Vo S, Foroosh H et al. Application of radial basis functions to shape description in a dual-element off-axis magnifier[J]. Optics Letters, 33, 1237-1239(2008). http://www.opticsinfobase.org/abstract.cfm?uri=ol-33-11-1237

[7] Cheng D W, Wang Y T, Hua H et al. Design of an optical see-through head-mounted display with a low f-number and large field of view using a freeform prism[J]. Applied Optics, 48, 2655-2668(2009).

[8] Zheng Z R, Liu X, Li H F et al. Design and fabrication of an off-axis see-through head-mounted display with an x-y polynomial surface[J]. Applied Optics, 49, 3661-3668(2010).

[9] Tong J B, Cui Q F, Xue C X et al. Optical design of a off-axis dual-channel helmet mounted display[J]. Acta Optica Sinica, 30, 2662-2667(2010).

[10] Yang B, Wei X N, Zhang W et al. Design method of a free-form HMD system with large pupil size[J]. Acta Photonica Sinica, 40, 1051-1054(2011).

[11] Li H, Zhang X, Wang C et al. Optical design of an avionic helmet-mounted displays using freeform surface[J]. Acta Optica Sinica, 34, 0322001(2014).

[12] Pan J W, Chiang C W, Huang K D et al. Demonstration of a broad band spectral head-mounted display with freeform mirrors[J]. Optics Express, 22, 12785-12798(2014). http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-11-12785

[13] Bauer A, Rolland J P. Visual space assessment of two all-reflective, freeform, optical see-through head-worn displays[J]. Optics Express, 22, 13155-13163(2014). http://www.opticsinfobase.org/abstract.cfm?URI=oe-22-11-13155

[14] Pang Z H, Fan X W, Ma Z et al. Free-form optical elements corrected aberrations of optical system[J]. Acta Optica Sinica, 36, 0522001(2016).

[15] Shi H D, Zhang X, Wang L J et al. Aberration properties of off-axis freeform surface optical system[J]. Acta Optica Sinica, 36, 0708001(2016).

[16] Liu X L, Zhang X D, Xu H Y et al. Machining error analysis of freeform surface off-axis three-mirror system based on optical performance evaluation[J]. Acta Optica Sinica, 37, 0812005(2017).

[17] Cakmakci O, Thompson K, Vallee P et al. Design of a free-form single-element head-worn display[J]. Proceeding of SPIE, 7618, 761803(2010). http://spie.org/Publications/Proceedings/Paper/10.1117/12.840716