JPS622213A - Optical filter element - Google Patents

Abstract

PURPOSE:To obtain a transmission type optical filter element which can select an optional wavelength near a Bragg wavelength and can be variably tuned by inserting an optically coupled phase modulation region between optical waveguides having plural distribution feedback regions and adjusting the optical phase difference of the respective distribution feedback regions from the outside. CONSTITUTION:The optical filter element is constituted of a buffer layer 2 epitaxially grown on a semiconductor substrate 1, the optical waveguide layer 3 including the distribution feedback regions 31 and the phase modulation region 32, a clad layer 4, an electrode forming layer 5, an n side electrode 6, a p side electrode 7 and an antireflection film 8. The optical waveguide layer 3 consists of undoped In0.84Ga0.16As0.36P0.64 and the average thickness in the part of the distribution feedback regions 31 is 0.1mum. The thickness in the part of the phase modulation region 32 is 0.2mum. The electrode forming layer 5 and the p side electrode 7 positioned in the part of the distribution feedback regions 31 are removed by chemical etching so that current is not injected to the regions 31.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an optical filter element.

(Prior Art) Optical filter elements, which have the function of selecting an optical signal of an arbitrary wavelength from a wavelength multiplexed optical signal, are key devices that can be applied to a wide range of applications such as optical transmission, optical conversion, and optical information processing. There is one. In any of these applications, the characteristics of the optical filter element are required to have sufficient wavelength selectivity and a wide range of selective wavelengths and variable tuning width. Furthermore, since optical integrated circuit structure is essential, it is also necessary to be a transmission type wavelength selection filter that transmits only a desired wavelength.

Conventionally, several studies have been made regarding transmission type wavelength selection filters. Among these, an optical filter element has a structure in which a wavelength-selective optical feedback structure is provided in an optical amplification element using a semiconductor active layer, and the selected wavelength can be tunable by changing the concentration of carriers injected into the active layer. It is expected to be an optical filter element suitable for transmission-type optical integration. In particular, as an optical feedback structure, a distributed feedback structure consisting of a diffraction grating is more advantageous than a Fapley-Bello resonator using a cleavage in terms of wavelength selectivity and optical integration, and optical filter elements using these structures Proposals and theoretical studies have also been carried out (Optics-Communication).
s Communication) Volume 10, page 120).

(Problems to be Solved by the Invention) However, these optical filter elements that have a distributed feedback structure in the optical amplification element that have been proposed and studied conventionally have a problem in that the active layer is When adjusting the injected carrier concentration, the optical gain for the selected wavelength,
Since the spontaneous emission light intensity also changes, the range of carrier concentration injected into the active layer is narrowly limited in principle in order to obtain the wavelength selectivity and signal intensity ratio to noise required for an optical filter element, and as a result, the range of the carrier concentration injected into the active layer is narrowly limited. This method has the disadvantage that a variable tuning width of the selected wavelength cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide an easily manufactured optical filter element that can provide a wide variable tuning width of selected wavelengths.

(Means for Solving the Problems) The optical filter element of the present invention includes a plurality of distributed feedback regions, and an optical filter element which is inserted between the distributed feedback regions and whose modulation degree can be controlled from an optically coupled external device. It consists of a phase modulation region.

(Function) The optical structure characteristics of a guiding waveguide having multiple distributed feedback structures optically coupled are such that when there is no optical gain in the transmission wavelength region, when the optical phase of each distributed feedback region is aligned, A transmission blocking wavelength range of several to several tens of degrees is formed around the Bragg wavelength determined by the optical period of the diffraction grating, but if the optical phase of each distributed feedback region is shifted, transmission blocking occurs. The wavelength range is divided, and a narrow transmission wavelength range of about 1 to 2 wavelengths is generated between the transmission blocking wavelength ranges. If an optically coupled phase modulation region is inserted between a leading waveguide having a plurality of distributed feedback regions, and the optical phase of each distributed feedback region is adjusted from the outside, it is possible to adjust the wavelength from several to several tens of times around the Bragg wavelength. A tunable transmission optical filter element that can select any wavelength in a wavelength range to a certain extent is obtained. In addition, since there is no need to have optical gain in the transmission wavelength range, if the leading waveguide is made of a semiconductor with a composition shorter than the transmission wavelength, a large wavelength selection range can be obtained by carrier injection, and furthermore, noise reduction due to spontaneous emission can be achieved. No deterioration of signal strength ratio occurs.

(Example) Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of an embodiment of the present invention in the direction of amplifying light. The optical filter element of this embodiment includes a buffer layer 2 epitaxially grown on a semiconductor substrate 1, an optical waveguide layer 3 including a distributed feedback region 31 and a phase modulation region 32, a cladding layer 4, an electrode forming layer 5, an n-side electrode 6,
It is composed of a p-side electrode 7 and an antireflection film 8. The semiconductor substrate 1 has a (100) orientation, and Sn is 1×1018c.
The buffer layer is made of InP doped with m-3 to a thickness of 10011 m, the buffer layer is made of InP doped with Sn to a thickness of lpm, and the optical waveguide layer 3 is made of undoped '0.84GaO, 16As0.36P0. The average thickness of the distributed feedback region 31 is 0.1.
pm, and the thickness of the phase modulation region 32 is 0.2 pm. The cladding layer 4 is made of InP doped with 5 x 1017 cm-3 of Zn and has a thickness of 2 pm, and the electrode forming layer 5 is made of InP doped with 5 x 1017 cm-3 of Zn.
InO, 84G doped with n of I x 1019 cm-3
It is made of aO, 16As0.36P0.64 and has a thickness of 0.
It is 5pm.

The n-side electrode 6 is made of An-Ge-Ni alloy and has a thickness of 0.3
pm, the p-side electrode 7 is made of an An-Zn alloy and has a thickness of 0.5 mm.
3pm, and the antireflection film 8 is made of 5L3N4 and has a thickness of 19
There are 00 people. A diffraction grating created by three-beam interference method is formed in the distributed feedback region 31, and the period is 1805.
The depth of the grid is 600 people. Also, the length of the element is 3
00pm, and the phase modulation region 32 is located at the center and has a length of 1100p. Then, the electrode formation layer 5 and the p-side electrode 7 located in the distributed feedback region 31 are removed by chemical etching, so that no current is injected into the distributed feedback region 31.

During operation, this optical filter element has a p-side electrode 7
A control current injected into the phase modulation region 32 from the control current selects and extracts an optical signal of an arbitrary wavelength from the wavelength multiplexed optical signal near the Bragg wavelength of the distributed feedback structure, which is incident from one end face of the element. be able to. In order to explain the operating principle of the present invention, FIG. FIG. 3 is a diagram showing a phase difference as a parameter. When the optical phase difference is zero, it becomes a waveguide type optical filter with a conventional distributed feedback structure, and there is one transmission blocking wavelength region near the Bragg wavelength, and all optical signals with wavelengths near the Bragg wavelength are reflected. and does not pass through. On the other hand, if the refractive index of the waveguide in the phase modulation region is changed to give an optical phase difference of, for example, 1/8 wavelength, two divided transmission blocking wavelength bands will appear, large and small.
The light of wavelength λ1 sandwiched between them is completely transmitted without being reflected. This transmission wavelength can be changed from λ1 to λ3 in accordance with the optical phase difference, as shown in FIG.

That is, in FIG. 2, λ1. λ2. If a three-wave multiplexed optical signal of λ3 is input to one end of an optical filter element, an optical signal of an arbitrary wavelength can be tuned by the phase modulation region and selectively extracted.

Specifically, to describe the design value calculated for the example, the coupling coefficient of the distributed feedback structure is about 200 cm-1.

If the wavelength selectivity required for an optical filter element is 10 dB, the amount of optical phase modulation that always provides a wavelength selectivity of 10 dB for transmitted waves is between 1/8 wavelength and 3/8 wavelength, and the corresponding transmitted wavelength The range of change is 16 people. On the other hand, a current of 1×101 is applied to the phase modulation region by current injection.
By injecting carriers of about 8 cm -3 , the refractive index of the waveguide changes, and the optical phase of the bone can be changed by up to half a wavelength. Therefore, since the 10 dB attenuation width of the transmitted wavelength is two, it becomes possible to select any wavelength from optical signals wavelength-multiplexed with a maximum of about 8 channels around the Bragg wavelength.

Note that the material and composition of the element need not be limited to the above-mentioned embodiments, and may be other semiconductor materials or dielectric materials. The phase modulation mechanism does not need to be limited to carrier injection; it may be any phenomenon that can obtain the necessary refractive index change, such as the electro-optic effect or the temperature dependence of the refractive index of a dielectric material. It's okay. Further, the guiding waveguide structure may be of any structure, not limited to a planar structure or a buried structure, as long as it has the function of guiding light, and may be a solid structure that allows light to enter and pass in the stacking direction. . Further, the distributed feedback structure is not limited to a waveguide type in which a diffraction grating is formed in the leading waveguide, but may be a solid structure in which layers having different refractive indexes are alternately laminated.

(Effects of the Invention) Finally, to summarize the features of the present invention, each distributed feedback can be An object of the present invention is to obtain a transmissive optical filter element capable of variable tuning that allows selection of any wavelength in the vicinity of the Bragg wavelength by externally adjusting the optical phase difference of the regions.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is a diagram showing transmittance characteristics of an optical filter element of the embodiment. In the figure, 1
is a semiconductor substrate, 2 is a buffer layer, 3 is a leading waveguide, 31 is a distributed feedback region, 32 is a phase modulation region, 4 is a cladding layer,
5 is an electrode formation layer, 6 is an n-side electrode, 7 is a p-side electrode, and 8 is an antireflection film. 31, Distribution return '11L Kasumi'

Claims (1)

[Claims] An optical filter element comprising a plurality of distributed feedback regions and a phase modulation region which is inserted in an optically coupled state between the distributed feedback regions and whose degree of modulation can be controlled from the outside.