JPS63253335A - Optical filter element - Google Patents

Abstract

PURPOSE:To obtain an optical filter element having tens of channels or more that can provide the variable tuning width of a large selective wavelength by optically connecting a distribution feedback area with a phase, shift structure and an active area serially, and making to the both end surfaces of the element into non-reflection structure and controlling a phase shifting amount. CONSTITUTION:The distribution feedback area with the phase shift structure is composed of a DBR area 200 and a phase control area 210. The phase shifting amount can be adjusted by pouring a current to the phase shifting area from the outside. Firstly, a lambda/4 shift diffraction grating is formed in the DBR area 200 of an n-InP substrate 110. Secondly, a 1st LPE growth leads a non-dope InGaAsP light guide layer 120, an n-InP buffer layer 130, a non-dope active layer 140 and a p-InP clad layer 150 to grow in that order. Thirdly, the InP clad layer 150 and the active layer 140 apart from the active area 100 are selectively removed, and during the 2nd LPE growth a p-InP clad layer 160 is fully formed. After that, an SiN film 170 is formed in order to keep the reflectance of the both ends of the element below 1%. Thus any wavelength can be selected.

Description

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

(Prior Art) Optical filter elements, which have the function of selecting an arbitrary optical signal from wavelength-multiplexed optical signals, are one of the key devices that can be applied to a wide range of applications such as optical transmission, optical exchange, and optical information processing. be. In any application, the characteristics of the optical filter element include sufficient wavelength selectivity and wide tunability of selected wavelengths.
Tuning range is required. Further, since optical integrated circuit structure is essential, it is also necessary that the transmission type wavelength selection 7 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 an optical feedback structure with wavelength selectivity is provided within 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 also attracting high expectations because it is suitable for transparent integration. In particular, as an optical feedback structure, a distributed feedback structure consisting of a diffraction grating is more advantageous than a Fap I Leuberot resonator between folds in terms of wavelength selectivity and optical integration, and optical filters using such a structure Element proposals and theoretical studies have also been made. (Optix Communications (Opt.
ics Communications) Volume 10 12
(See page 0) (Problems to be Solved by the Invention) However, these optical filter elements that have a distributed feedback structure in the optical amplification element that has been proposed and studied in the past do not have an active layer for tuning the selected wavelength. When adjusting the concentration of carriers injected into the filter, the optical gain and spontaneous emission intensity for the selected wavelength also change. In principle, the carrier concentration injected into the active layer is narrowly limited, and as a result, the variable range of the selected wavelength is as small as a few wavelengths, so it has the disadvantage that it can only be used as a filter for a few channels.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical filter element having several tens of channels or more, which has an amplification function and can obtain a large variable tuning width of a selected wavelength, eliminating the above-mentioned drawbacks.

(Means for solving the problem) In the optical filter element of the present invention, a distributed feedback region having a phase shift structure and an active region are optically coupled and arranged in series, and both end surfaces of the element are non-reflective. The phase shift region is characterized in that the shift amount of the phase shift region can be controlled from the outside.

(Function) The optical transmission characteristics of a guiding waveguide having a distributed feedback structure are determined by the optical period of the diffraction grating when there is no optical gain in the transmission wavelength region, and when the optical phase of each distributed feedback region is the same. One transmission-blocking wavelength range of about several dozen is formed around the Bragg wavelength determined by . On the other hand, if the optical phase is shifted by n on both sides of the center of the distributed feedback region (in this case, if the wavelength of the light propagating in the element is λ, then the pitch of the diffraction grating is shifted by v4) Therefore, M
In the 4-shift groove structure), the transmission blocking wavelength range is divided, and a narrow transmission wavelength range of about 2 wavelengths or less is generated in the center of the transmission blocking wavelength range of about 10 wavelengths described above. If the optical waveguide layer with a distributed feedback region having a J4 shift structure is constructed of a semiconductor with a composition on the shorter wavelength side than the transmission wavelength, there will be no optical gain. A large wavelength selection width can be obtained with the narrow width at the bottom, and furthermore, the deterioration of the noise intensity ratio due to spontaneous emission light does not occur.

Furthermore, by injecting a current into the phase shift region from the outside, the amount of phase shift can be adjusted. Depending on the amount of phase shift, the transmission characteristics change as shown in Figure 3, and a tunable transmission optical filter element can select any wavelength in the wavelength range of several to several tens of degrees centered around the Bragg wavelength. can get. In other words, by varying the phase shift amount, compared to the case where the phase shift amount is fixed only to M4,
Furthermore, the variable wavelength width can be increased.

Since the above-mentioned leading waveguide layer has no gain, the active region and the distributed feedback region may be optically coupled to form an optical filter element having an amplification function.

That is, if the structure is such that light is injected into the active region, amplified, and then transmitted through the distributed feedback region, an optical filter element having an amplification function can be obtained.

There is one thing to note here. That is, both end faces of the element must have a non-reflection structure. The reason for this is that if it were not made to have a non-reflective structure, it would oscillate as a DBR laser.

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

FIG. 1 is a perspective view showing the structure of an optical filter element according to an embodiment of the present invention. The structure of this embodiment will be explained below while following the manufacturing procedure. First, n-type InP substrate 11
An A/4 shift diffraction grating with a period of 2400 is formed in the DBR region 200 above 0. Next, the non-doped InGaAsP optical guide layer 120 (λg=
1°3 pm, thickness 0.3 pm), n-type InP buffer layer 130 (thickness 0°1 pm), non-doped active layer 140 (
λg=1.53 pm, thickness 0°1 pm), and a p-type InP cladding layer 150 (thickness 0.2 pm) is sequentially grown. Next, the InP cladding layer 150 and the active layer 140 other than the active region 100 are selectively removed. Next, in the second LPE growth, the entire p-type InP cladding layer 1 is
Form 60.

Next, in order to form a buried structure, mesa etching is performed, and then buried growth is performed by a third LPE growth. Here, a double channel planar embedding structure was used as the embedding structure.

Finally, after forming electrodes on the substrate side and the growth layer side, in order to electrically isolate between the active region 100 and the DBR region 200, and between the DBR @ region 200 and the phase control region 210, A groove with a width of 20 pm is formed except for. Thereafter, a SiN film 170 is formed using a plasma CVD apparatus in order to reduce the reflectance at both ends of the element to 1% or less. The lengths of the active region 100, DBR region 200, and phase control region 210 are 1100p and 240pm, respectively.
, 20 μm. In this embodiment, the distributed feedback region having a phase shift structure is a DBR region 200 and a phase control region 2.
It consists of 10.

An example of the characteristics of the device prototyped in this way is shown below. When a current of 50 mA is injected into the amplification region 100, the extinction ratio is 20.
dB or more, the 10 dB attenuation width of the transmitted wavelength was 0.5 people. Further, when no current is applied to the DBR region 200 and the phase control region 210, the transmission wavelength is 1.5563 pm.

80m for both DBR area 200 and phase control area 210
When the current of A is increased, the transmitted wavelength is 1.5505 pm.
Therefore, the transmitted wavelength changed continuously by 58 people. moreover,
When the current injected into the DBR region 200 is fixed at 80 mA and the current injected into the phase control region 210 is increased from 80 mA to 160 mA, the transmission wavelength continuously shifts to the shorter wavelength side and becomes 1.5497 pm. Ta. The phase shift amount at this time corresponds to 3υ16. The depth of the diffraction grating after crystal growth is 500 mm, and the transmission blocking wavelength range is 65 mm.
It was a person.

FIG. 2 shows the transmission characteristics when the same magnitude of current is injected into both the DBR region 200 and the phase control 210.

From this figure, it is possible to select any wavelength from signals wavelength-multiplexed at intervals of about 0.5 degrees within about half of the transmission blocking wavelength range, that is, within a range of about 30 people. Furthermore, by fixing the injection current to the DBR region 200 and injecting the current into the phase control region, the range of 0.5 to 0.
It is possible to select any wavelength from signals wavelength-multiplexed at intervals of seven people. That is, it can be used as a wavelength tunable filter with about 70 channels.

Note that the material and composition of the element need not be limited to the above-mentioned embodiments, and may be other semiconductor materials, dielectric materials, or the like. Further, the phase shift structure may also be a so-called isometric phase shift structure, which has a uniform diffraction grating and has a waveguide having a different width or a different thickness. In addition, the guiding waveguide structure is not limited to a planar structure or a buried structure, but may be any structure as long as it has the function of guiding light; for example, it may be a solid structure that allows light to enter and pass in the stacking direction. good. 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. Further, the non-reflective structure may also be a window structure or a multilayer coating.

(Effects of the Invention) Conventional optical filter elements were limited to a few channels, but the optical filter element of the present invention makes it possible to select any wavelength from a wavelength-multiplexed optical signal of up to 70 channels. .

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the structure of an optical filter element according to an embodiment of the present invention. FIG. 2 shows the transmission characteristics when the same magnitude of current is passed through the DBR region and the phase control region of the optical filter element of this example. FIG. 3 shows the transmission characteristics when the amount of phase shift changes. In the figure, 100 - active region, 200 - DBR region 110 - substrate,
120~light guide layer 130~buffer layer, 140~active layer 150~cladding layer, 160~cladding layer IIN
T! Figure 2 Wavelength (pm)

Claims (1)

[Claims] A distributed feedback region having a phase shift structure and an active region are optically coupled and arranged in series, both end faces of the element have a non-reflection structure, and the amount of shift of the phase shift region can be controlled from the outside. An optical filter element characterized by: