Design of transceiver separation structure for orthogonal cascaded liquid crystal polarization gratings

$Diffraction properties of passive LCPG: (a) Incident light is right-handed circular polarization; (b) Incident light is left-handed circular polarization$

Fig. 2. Diffraction properties of passive LCPG: (a) Incident light is right-handed circular polarization; (b) Incident light is left-handed circular polarization

Fig. 3. Passive LCPG layer with two LC-AHWPs and two LCPGs

Fig. 4. Beam transceiver separation structure using OC-LCPGS

Fig. 5. Experimental diagram of OC-LCPGs receiving and transmitting separation structure verification

$Diffraction efficiency of different LCPG at different angles$

Fig. 6. Diffraction efficiency of different LCPG at different angles

$Diffraction efficiency of LCPG with mirror symmetry at different angles$

Fig. 7. Diffraction efficiency of LCPG with mirror symmetry at different angles

Table 1. Control coefficient and polarization state change at different angles

Table 1. Control coefficient and polarization state change at different angles

Modulation angle/(°)	Polarization state of incident light	Phase delay of AHWP1	Polarization state after AHWP1	Polarization state after LCPG1	Phase delay of AHWP2	Polarization state after AHWP2	Polarization state after LCPG2
2θ	RCPL	0	RCPL	LCPL	π	RCPL	LCPL
0		0	RCPL	LCPL	0	LCPL	RCPL
−2θ		π	LCPL	RCPL	π	LCPL	RCPL
2θ	LCPL	π	RCPL	LCPL	π	RCPL	LCPL
0		0	LCPL	RCPL	0	RCPL	LCPL
−2θ		0	LCPL	RCPL	π	LCPL	RCPL

Table 2. Control coefficient and polarization state change at different angles reverse light path

Table 2. Control coefficient and polarization state change at different angles reverse light path

Modulation angle/(°)	Polarization state before LCPG2	Polarization state before AHWP2	Phase delay of AHWP2	Polarization state before LCPG1	Polarization state before AHWP1	Phase delay of AHWP1	Polarization state before AHWP1
2θ	RCPL	LCPL	π	RCPL	LCPL	0	LCPL
0	LCPL	RCPL	0	RCPL	LCPL	0	LCPL
−2θ	LCPL	RCPL	π	LCPL	RCPL	π	LCPL
2θ	RCPL	LCPL	π	RCPL	LCPL	π	RCPL
0	RCPL	LCPL	0	LCPL	RCPL	0	RCPL
−2θ	LCPL	RCPL	π	LCPL	RCPL	0	RCPL

Table 3. Control parameters of AHWP in each layer

Table 3. Control parameters of AHWP in each layer

Realization angle	0°（MD 1.25° layer）		−1.25°（SD 1.25° layer）
Wave plate serial number	0.625°	0.625°	0.625°	0.625°
Control coefficient	0	0	1	1
Realization angle	2.5°（MD 2.5° layer）		2.5°（SD 2.5° layer）
Wave plate serial number	1.25°	1.25°	1.25°	1.25°
Control coefficient	0	1	0	0
Realization angle	0°（MD 5.0° layer）		−5°（SD 5.0° layer）
Wave plate serial number	2.5°	2.5°	2.5°	2.5°
Control coefficient	0	0	0	1
Realization angle	0°（MD 10.0° layer）		−10°（SD 10.0° layer）
Wave plate serial number	5.0°	5.0°	5.0°	5.0°
Control coefficient	0	0	1	1
Realization angle	20°（MD 20.0° layer）		0°（SD 20.0° layer）
Wave plate serial number	10.0°	10.0°	10.0°	10.0°
Control coefficient	0	1	0	0

Table 4. Polarization states before and after each element of OC-LCPGS

Table 4. Polarization states before and after each element of OC-LCPGS

Layer	MD 1.25° layer	SD 1.25° layer	MD 2.5° layer	SD 2.5° layer	MD 5.0° layer	SD 5.0° layer	MD 10.0° layer	SD 10.0° layer	MD 20.0° layer	SD 20.0° layer
Realization angle/(°)	0	−1.25	2.5	2.5	0	−5	0	−10	20	0
Polarization state after layer	RCPL	RCPL	LCPL	LCPL	LCPL	RCPL	RCPL	RCPL	LCPL	LCPL

Table 5. Polarization states before and after each element of OC-LCPGS under the condition of reverse incidence

Table 5. Polarization states before and after each element of OC-LCPGS under the condition of reverse incidence

Layer	SD 20.0° layer	MD 20.0° layer	SD 10.0° layer	MD 10.0° layer	SD 5.0° layer	MD 5.0° layer	SD 2.5° layer	MD 2.5° layer	SD 1.25° layer	MD 1.25° layer
Realization angle/(°)	0	−20	10	0	5	0	−2.5	−2.5	1.25	0
Polarization state after layer	LCPL	RCPL	RCPL	RCPL	RCPL	LCPL	LCPL	LCPL	RCPL	LCPL

Table 6. Composition and index of test system

Table 6. Composition and index of test system

Component	Parameter	Value
Laser 1	Wavelength/nm	630
Laser 1	Optical power/mW	3.20
Laser 2	Wavelength/nm	630
Laser 2	Optical power/mW	1.50
PBS	Transmittance	P：96%; S：94%
QWP	Transmittance	96%
HWP	Transmittance	96%
Grating	Linear density of grating 1/lp·mm⁻¹	159
	Linear density of grating 2/lp·mm⁻¹	159
	Linear density of grating 3/lp·mm⁻¹	286
	Linear density of grating 4/lp·mm⁻¹	286
	Transmittance	As shown in Fig.6
	Thickness/mm	0.45±0.04
	Material	D263

Table 7. Transmittance at different modulation angles

Table 7. Transmittance at different modulation angles

Main order angle/(°)	Transmittance of 1^st measurement of S light	Transmittance of 2^nd measurement of S light	Transmittance of 3^rd measurement of S light	Average transmittance of S light	Average transmittance of P light
0	81%	82%	81%	81%	＜1%
10	61%	61%	61%	61%	＜1%
−10	61%	61%	61%	61%	＜1%
20	52%	50%	53%	52%	＜1%
−20	50%	50%	51%	50%	＜1%
30	41%	39%	40%	40%	＜1%
−30	36%	37%	36%	36%	＜1%

Table 8. Incident angle at different modulation angles