Standard filter denomination

Nomenclature of standard filters

Read the following nomenclature description to know more about how Delta Optical Thin Film specifies filter names.

Bandpass Filters

Denomination
All types of bandpass filters (Laserline, narrow band, broad band) use the same denomination standard:
BP λc / Δλ

Centre wavelength λC
λC is the arithmetic mean of the two wavelengths where the filter transmits: ½ x Taverage.
λC = (λFWHM2 - λFWHM1) / 2
λFWHM1= λ1 (½ x Taverage)
λFWHM2= λ2 (½ x Taverage)

Where Taverage is the average transmission in the passband.

Bandwidth: FWHM Δλ
The FWHM (Full Width Half Maximum) is described as follows:
FWHM = Δλ = (λFWHM2 - λFWHM1)

Transmission band: T(λ1 - λ2)
T (λ1 - λ2) is the wavelength bandwidth where the transmission is high and T is the associated minimum average transmission in the passband. This may also be divided into several bands, e.g.

λ1 - λ2 with minimum average transmission T1
λ3 - λ4 with minimum average transmission T2
λ5 - λ6 with minimum average transmission T3

Rejection band: Tb(λ1 - λ2)
Tb (λ1 - λ2) is the wavelength bandwidth where the transmission is low and Tb is the associated average transmission in the band. This may also be divided into several bands, e.g.

λ1 - λ2 with minimum average blocking (OD5 for example) Tb1
λ3 - λ4 with minimum average blocking (OD5 for example) Tb2
λ5 - λ6 with minimum average blocking (OD5 for example) Tb3

Tolerance numbers
Typical tolerance numbers are given on the center wavelength and the bandwidth.

Example: BP 450/40 with 450 +/- 2nm and 40 +/- 2nm

Edge Filters

Denomination
- Long Wave Pass: LP λC
- Short Wave Pass: SP λC

Edge wavelength λC
λC is the wavelength where the transmission T of the filter has reached 50% of the filter's maximum transmission level.

Example: The nomenclature for an edge filter is e.g. LP 510 where λC = 510 nm.

Rejection band
Tb (λ1 - λ2) is the wavelength bandwidth where the transmission is low and Tb is the associated average transmission in the band. This may also be divided into several bands, e.g.

λ1 - λ2 with minimum average blocking (OD5 for example) Tb1
λ3 - λ4 with minimum average blocking (OD5 for example) Tb2
λ5 - λ6 with minimum average blocking (OD5 for example) Tb3

Transmission band
T(λ1 - λ2) is the wavelength bandwidth where the transmission is high and T is the associated average transmission in the passband. This may also be divided into several bands, e.g.

λ1 - λ2 with minimum average transmission T1
λ3 - λ4 with minimum average transmission T2
λ5 - λ6 with minimum average transmission T3

Tolerance numbers
Typical tolerance numbers are given on the edge wavelength.

Example: LP 490 +/- 2nm.

Dichroics / Colour Beamsplitters

Denomination
- Long Wave Pass Dichroic: DCLP λC
- Short Wave Pass Dichroic: DCSP λC

Edge wavelength λC
λC is the wavelength where the transmission T of the filter has reached 50% of the average transmission level.

Example: The nomenclature for a dichroic is e.g. DCLP 395 where λC = 395 nm.

Reflection band R (λ1 - λ2)
R (λ1 - λ2) is the wavelength bandwidth where the reflection is high and R is the associated average reflection in the band. This may also be divided into several bands, e.g.

λ1 - λ2 with minimum average reflection R1
λ3 - λ4 with minimum average reflection R2
λ5 - λ6 with minimum average reflection R3
Transmission band T (λ1 - λ2)
T (λ1 - λ2) is the wavelength bandwidth where the transmission is high and T is the associated average transmission in the passband. This may also be divided into several bands, e.g.

λ1 - λ2 with minimum average transmission T1
λ3 - λ4 with minimum average transmission T2
λ5 - λ6 with minimum average transmission T3

Tolerance numbers
Typical tolerance numbers are given on the edge wavelength.

Example: DCLP 490 +/- 2nm.