Components for Optical Parametric Oscillators (OPO)

Mirrors for OPOs are optimized for separation of the pump laser, signal and idler wavelengths. This application requires a broad reflectance band for the signal wavelength and a wide range of high transmittance for the idler and pump wavelengths. Moreover, most of the optics show smooth group delay (GD) and group delay dispersion (GDD) spectra. Thus, wide tuning ranges for the signal and the idler wavelengths can be achieved. This enables the operation of OPOs with fs-pulses. Broadband output couplers are also available. Center wavelength and tuning range can be adjusted according to customer specifications. All OPO coatings are produced by magnetron sputtering. This process guarantees that the optical parameters are environmentally stable, because the coatings are compact, free of water and adhere strongly to the substrate in spite of the extreme coating thickness of 20 – 30 μm. This makes sputtered OPO coatings ideal for application in harsh environments.

Cavity Mirrors for AOI = 0°

Fig.1:Reflectance, GD and GDD spectra of a broadband HR mirror for the signal wavelength: HR (0°, 1000 – 1600 nm) > 99.9 %

a)Reflectance vs. wavelength

b)GDD vs. wavelength

Fig.2:Reflectance, GD and GDD spectra of a dual HR mirror for the signal and idler wavelengths:
HR (0°, 1400 – 1800 nm) > 96 % + HR (0°, 2900 – 4900 nm) > 93 %

a)Reflectance vs. wavelength

b)GD and GDD vs. wavelength

Pump Mirrors and Separators for AOI = 0°

Fig.3:Reflectance, GD and GDD spectra of an OPO pump mirror

a)Reflectance vs. wavelength

b)GD and GDD vs. wavelength

This type of mirror separates the pump and signal wavelengths while suppressing the idler wavelength:
R (0°, 700 – 850 nm) < 10 % + HR (0°, 900 – 1600 nm) > 99.8 % + R (0°, 1800 – 5000 nm) < 60 %.

Fig.4:Reflectance, GD and GDD spectra of a separator for the signal and idler wavelengths

a)Reflectance vs. wavelength

b)GD and GDD vs. wavelength

Edge filters separating signal and idler wavelengths can be used as broadband out-coupling mirrors for the idler:
HR (0°, 1100 – 1600 nm) > 99.8 % + R (0°, 1730 – 2900 nm) < 10 %
These filters can also be provided with a band of high reflectance or high transmittance for the pump wavelengths or for the second harmonic of the signal wavelengths
LAYERTEC recommends undoped YAG or sapphire as substrate material if high transmittance for the idler wavelengths is required (see also page Fused Silica for transmittance curves)

Fig.5:Reflectance spectrum of a broadband mirror for the NIR:
HR (0°, 2300 – 4000 nm) > 99 %

Fig.6:Reflectance spectrum of a separator for the signal and idler wavelengths:
HR (0°, 2050 – 3500 nm) > 99 % + R (0°, 1600 – 1930 nm) < 5 %

Output Couplers

Fig.7:Reflectance and GDD spectra of different broadband output couplers for the signal wavelength range.

a)Reflectance vs. wavelength

b)GDD vs. wavelength (The spectra shown are calculated for the 75 % output coupler, but the spectra for other reflectance values are very similar.)

The reflectance of output couplers and beam splitters can be adjusted according to customer specifications.

Beam Splitters for AOI = 45°

Fig.8:Reflectance and GDD spectra of a broadband beam splitter for p-polarized signal and idler radiation: PRp (45°, 1100 – 2400 nm) = 50 % ±5 %

a)Reflectance vs. wavelength

b)GDD vs. wavelength

Special Output Couplers for AOI = 0°

Fig.9:Reflectance spectrum of a special output coupler:
PR (0°, 2000 – 3150 nm) = 90 % ±3 %
+ R (0°, 1400 – 1700 nm) < 3 %

Fig.10:Reflectance spectrum of a special output coupler:
PR (0°, 1350 – 2000 nm) = 98 % ±0.5 %
+ R (0°, 1000 – 1100 nm) < 3 %
+ R (0°, 2200 – 5000 nm) < 20 %

The output couplers for the signal wavelengths Fig. 9 can suppress the idler and vice versa Fig. 10. These output couplers may also have a pump window.

Turning Mirrors and Separators for AOI = 45°

Fig.11:Reflectance, GD and GDD spectra of a turning mirror HRp (45°, 1450 – 2000 nm) > 99.8 %

a)Reflectance vs. wavelength

b)GD-Rp and GDD-Rp vs. wavelength

Turning mirrors and separators for pump, signal and idler are key components of OPOs. The spectral position of the reflectance and transmittance bands can be adjusted according to customer specifications. Please note that GD and GDD can only be optimized for s- or p-polarization while the reflectance is usually very high for both polarizations.

Fig.12:Reflectance, GD and GDD spectra of a separator for signal and idler

a)Reflectance vs. wavelength

b)GD and GDD vs. wavelength

A broad reflectance band for the signal is combined with a broad transmittance band for the idler:
HRp (45°, 1450 – 2000 nm) > 99.8 % + Rp (45°, 2350 – 4000 nm) < 10 %.

Fig.13:Reflectance, GD and GDD spectra of a separator for the signal and idler with high transmittance for the pump radiation

a)Reflectance vs. wavelength

b)GD and GDD vs. wavelength

This separator can be used to couple the pump radiation into the resonator:
HRs (45°, 770 – 930 nm) > 99.8 % + Rp (45°, 510 – 550 nm) < 1 % + Rp (45°, 1160 – 1900 nm) < 10 %.

Ultra Broadband Components for AOI = 45°

Fig.14:Reflectance spectrum of an ultra broadband separator for signal and idler wavelengths:
HRu (45°, 1000 – 2500 nm) > 98 %
+ Ru (45°, 4400 – 5000 nm) < 5 %

Edge Filters for AOI = 45°

Fig.15:Reflectance spectrum of an edge filter for the idler and signal wavelength range with high transmittance for the pump wavelength:
HRs (45°, 2150 – 2700 nm) > 99.9 %
+ Rs (45°, 2000 – 2070 nm) < 10 % + Rs (45°, 1064 nm) < 1 %

Fig.16:Reflectance spectrum of a broadband edge filter for the idler wavelength range with high transmittance for the pump wavelength:
HRs (45°, 3300 – 4200 nm) > 99.9 %
+ Rs (45°, 4500 – 4900 nm) < 6 % + Rs,p (45°, 1064 nm) < 5 %

Coatings on Nonlinear Optical Crystals AOI = 0°

Fig.17:Reflectance spectrum of an AR coating on lithium niobate:
R (0°, 1064 nm) < 0.5 % + R (0°, 1750 – 2750 nm) < 1 %

Fig.18:Reflectance spectrum of an AR coating on lithium niobate:
R (0°, 1910 – 2030 nm) < 0.5 % + R (0°, 3200 – 4200 nm) < 1 %

Fig.19:Reflectance spectrum of an AR coating on lithium niobate:
R (0°, 1064 nm) < 0.5 %
+ R (0°, 1420 – 1640 nm) < 0.5 %
+ R (0°, 3150 – 3700 nm) < 2 %

Fig.20:Reflectance spectrum of a double reflector with two regions of high transmittance on lithium niobate:
HR (0°, 1010 – 1075 + 2750 – 3450 nm) > 99.8 %
+ R (0°, 700 – 900 + 1200 – 2400 nm) < 10 %