Dual transmission band interference filter

• US 6,407,863 B1
• Filed: 04/17/2000
• Issued: 06/18/2002
• Est. Priority Date: 04/20/1999
• Status: Expired due to Term

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Pelekhaty, Vladimir, Archambault, Jean Luc
• Primary Examiner(s): HENRY, JON W
• Application Number:
  US09/551,141
• Time in Patent Office: 792 Days
• Field of Search: 359/589, 359/588, 359/586, 359/580
• US Class Current: 359/589
• CPC Class Codes: G02B 5/288 comprising at least one thin film resonant cavity, e.g. in bandpass filters

Abstract

A dual-band optical filter is disclosed which has two transmission bands. The first band is relatively narrow (about 1 nm) and encompasses a wavelength of about 1550 nm, while the second band is relatively broad (greater than 50 nm) to transmit wavelengths in a range of 1300-1400 nm. Accordingly, the filter can be used in wavelength division multiplexed communication systems to simultaneously select a payload channel having a wavelength of approximately 1550 nm, and a 1310 nm service channel.

Claims

1. An optical filter, comprising:

a first mirror layer;

a second mirror layer; and

a spacer layer provided between said first mirror layer and said second mirror layer;

said filter having a transmission spectrum, a first portion and a second portion, said second portion having a peak transmissivity of substantially 100% at a wavelength substantially equal to 1550 nm, and said first portion of said transmission spectrum having a transmissivity of substantially 100% over q band of wavelengths including 1310 nm.

2. An optical filter in accordance with claim 1, wherein said first mirror layer includes a plurality of dielectric layers.

3. An optical filter in accordance with claim 1, wherein a first wavelength (λ

₀) lies within said first portion of said transmission spectrum, and a second wavelength (λ

₁) lies within said second portion of said transmission spectrum, said first mirror comprising;

alternating first and second dielectric layers, each said first dielectric layers having a first refractive index (n_H(λ

₁)), and each said second dielectric layers having a second refractive index (n_L(λ

₁)), said first refractive index being greater than said second refractive index, said first and second refractive indices satisfying the following formula;

$\frac{n_H<br><br>\left({\mathrm{\lambda <br><br>}}_1\right)}{n_L<br><br>\left({\mathrm{\lambda <br><br>}}_1\right)}=\frac{1+r}{1-r}$

where r satisfies the following formula;

$r=\sqrt{1-{\left(\frac{\sin <br><br>\left(\frac{\mathrm{\pi <br><br>}}{2}<br><br>\frac{{\mathrm{\lambda <br><br>}}_0}{{\mathrm{\lambda <br><br>}}_1}\right)}{\sin <br><br>\left(\frac{\mathrm{\pi <br><br>}}{2}<br><br>\frac{\left(q-1\right)}{\left(q+1\right)}\right)}\right)}^2}$

where q is a sum of the number of said first and second dielectric layers.

4. An optical filter in accordance with claim 2, wherein said plurality of dielectric layers includes a first plurality of layers and a second plurality of layers, each said first plurality of layers including SiO₂ and each said second plurality of layers including Ta₂O₅.

5. An optical filter in accordance with claim 1, wherein said second portion of said transmission spectrum having a bandwidth of at least 50 nm.

6. An optical filter in accordance with claim 1, wherein said first mirror includes q dielectric layers, where q is an integer at least equal to 7, each of a first plurality of said q dielectric layers having a first refractive index and each of a second plurality of said q dielectric layers having a second refractive index, said first refractive index being greater than said second refractive index, each of a third plurality of said q dielectric layers having a third refractive index intermediate between said first and second refractive indices.

7. An optical filter in accordance with claim 6, wherein said q dielectric layers constitute a stack of layers having a first outermost layer and a second outermost layer, a first one of said third plurality of q dielectric layers being spaced from said first outermost layer by a first intermediate one of said q dielectric layers, and a second one of said third plurality of said q dielectric layers being spaced from said second outermost layer by a second intermediate one of said q dielectric layers.

8. An optical filter in accordance with claim 6, wherein said first one of said third plurality of said q dielectric layers is a substantially homogenous layer.

9. An optical filter in accordance with claim 6, wherein said first one of said third plurality of said q dielectric layers includes a plurality of dielectric layers collectively having a refractive index substantially equal to said third refractive index.

10. An optical filter in accordance with claim 9, wherein at least a first one of said plurality of dielectric layers within said first one of said third plurality of said q dielectric layers includes a material identical to that of said first plurality of q dielectric layers, and a second one of said plurality of dielectric layers within said first one of said third plurality of said q dielectric layers includes a material identical to that of said second plurality of q dielectric layers.

11. An optical filter in accordance with claim 6, wherein said first plurality of said q dielectric layers each includes SiO₂, and each said second plurality of said q dielectric layers includes Ta₂O₅.

12. An optical filter in accordance with claim 1, wherein a wavelength lies within said first portion of said transmission spectrum, said first mirror includes q dielectric layers, said q dielectric layers constitute a stack of layers having a first outermost layer and a second outermost layer, a first one of said q dielectric layers adjacent said first outermost layer having an optical thickness substantially equal to ¾

times said wavelength, and a second one of said q dielectric layers adjacent said second outermost layer having an optical thickness substantially equal to ¾

times said wavelength.

13. An optical filter in accordance with claim 1, wherein said first bandwidth has a magnitude of about 1 nm and said second bandwidth has a magnitude of at least 20 nm.

14. An optical filter in accordance with claim 1, wherein a wavelength within said first bandwidth has a value greater than a value of a wavelength within said second bandwidth.

15. An optical filter in accordance with claim 6, wherein said first refractive index is substantially equal to 2.05, said second refractive index is substantially equal to 1.44 and said third refractive index is substantially equal to 1.58.