JPS63223605A - Optical filter element - Google Patents

Abstract

PURPOSE:To obtain a variable tuning width of a large selection wavelength by forming both end faces of an element which is disposed with plural distributed feedback regions having phase shift structure and active regions in series and are coupled optically into non-reflection structure. CONSTITUTION:A lambda/4 shift diffraction grating is formed to the distributed feedback regions 201, 202 on an n-type InP substrate 110. After an InP clad layer 150 and active layer 140 of the regions 201, 202 are selectively removed, a p-type InP clad layer 160 is formed over the entire part. Grooves for electrical sepn. of amplifier regions 101, 102 and the regions 201, 202 are formed by executing mesa etching followed by embedment growth. An SiN film 170 is thereafter formed in order to decrease the reflectivity at both end faces of the element to <=1%. The oscillation of the element as a distributed feedback type laser is caused unless both end faces 170 have the nonreflection structure. Addition of the transmission prohibition wavelength region of the 2nd distributed feedback regions to the wavelength regions where the prohibition is heretofore not possible with the single distributed feedback region alone is thereby permitted and the wavelength selection width is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical filter element, and particularly to an optical filter element having a distributed feedback structure.

[Conventional technology]

Optical filter elements that have the function of selecting any optical signal from wavelength multiplexed optical signals are used in optical transmission and optical exchange.

It is one of the key devices that can be applied to a wide range of applications such as optical information processing. In any of the applications, the characteristics of the optical filter element are required to have sufficient wavelength selectivity and a wide variable tuning range of the selected wavelength. Furthermore, since optical integrated circuit structure is essential, it is also necessary to use 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 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 Fabry-Bello resonator between folds in terms of wavelength selectivity and optical integration. Element proposals and theoretical studies have also been made [Optics Communications (Opti
cs Communications) Volume 10.

See page 120].

[Problem that the invention seeks to solve]

However, in the optical filter elements that have a distributed feedback structure in the optical amplification element that has been proposed and studied in the past, when the carrier concentration injected into the active layer is adjusted to tune the selected wavelength, at the same time Since the optical gain and the spontaneous emission intensity also change, the carrier concentration injected into the active layer must be narrowly limited in principle in order to obtain the wavelength selectivity necessary for an optical filter element and to obtain the signal strength to noise ratio. As a result, the variable tuning range of the selected wavelength is as small as a few people, 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, eliminates the above-mentioned drawbacks, and is capable of obtaining a large variable tuning width of selected wavelengths.

[Means for solving problems]

In the optical filter element of the present invention, a plurality of distributed feedback regions having a phase shift structure and a plurality of active regions are arranged in series and optically coupled, and both end faces of the element have a non-reflection structure. It is characterized by

[Effect]

The optical transmission characteristic of an optical waveguide having a distributed feedback structure is that when it has no optical gain in the transmission wavelength range, when the optical phase of each distributed feedback region is aligned, the optical transmission characteristic is the Bragg wavelength determined by the optical period of the diffraction grating. A transmission-blocking wavelength range of about several dozen people is formed around the . On the other hand, if the optical phase is shifted by π 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 λ/4). Since it corresponds to
(called a λ/4 shift structure), the transmission blocking wavelength range is split, and there is a
A narrow transmission wavelength range of about two wavelengths or less is generated. This λ/
If an optical waveguide layer with a distributed feedback region with a 4-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 wide wavelength selection width can be obtained, and furthermore, the deterioration of the noise intensity ratio due to spontaneous emission light does not occur.

In addition, when a current is injected from the outside into the phase shift region, the amount of phase shift can be adjusted.The amount of phase shift can be adjusted to zero. ),
A tunable transmission optical filter element that can select any wavelength in a wavelength range of several to several dozen wavelengths centered on the Bragg wavelength can be obtained. That is, by making the phase shift amount variable, the variable wavelength width can be made larger than when the phase shift amount is fixed only to λ/4.

Since the optical waveguide layer described above has no gain, in order to construct an optical filter element with an amplification function, it is sufficient to optically couple the active region and the distributed feedback region. If the structure is such that the light is injected, amplified, and then transmitted through the distributed feedback region, an optical filter element with an amplification function can be obtained.

Here, there is one point that should be noted. That is, both end faces of the optical filter element must have a non-reflective structure. The reason for this is that if it does not have a non-reflection structure, it will oscillate as a DBR (distributed feedback) laser.

Now, the feature of the present invention is that the present invention has a configuration in which a plurality of distributed feedback (DBR) regions are arranged in series. If there is a single distributed feedback region, the wavelength selection width will be limited to half of the transmission blocking wavelength region. However, as in the present invention, by providing a plurality of distributed feedback regions and matching the transmission blocking wavelength range of the second distributed feedback region to the wavelength range that could not be blocked by a single distributed feedback region, the wavelength selection width can be increased. thick (can be)

〔Example〕

Next, embodiments of 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 1nP group wil
A λ/4 shift diffraction grating with a period of 2400 is formed in the distributed feedback (DBR) jJI region 201 and 202 on lo. Next, in the first LPE growth (liquid phase growth), the non-doped InGaAsP optical guide layer 120 (λ9 = 1.3
pta+thickness 0.3 μm), n-type InP buffer layer 130 (thickness 0.1 μm), non-doped active layer 1
40(λ, =1.537761.Thickness 0.1 #Il
+), I) type 1nP cladding layer 150 (thickness 0.2μ
m) are grown sequentially. Next, the distributed feedback area 201.202
The InP cladding layer 150 and active layer 140 are selectively removed. Next, a p-type 1nP cladding layer 160 is formed over the entire structure by a second LPE growth.

Next, mesa etching is performed to form a buried structure, 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, a groove with a width of 20 μm is formed except for the vicinity of the central mesa in order to electrically isolate the amplification region 100.101 and the distributed feedback region 201.202. form. Thereafter, a SiN film 170 is formed using a plasma CVD apparatus in order to reduce the reflectance of both end faces of the element to 1% or less.

Amplification regions 101, 102, distributed feedback regions 201, 20
The lengths of 2 are 100 μm, 100 μm, and 5
QQμm is 500μm.

An example of the transmission characteristics of the optical filter element of this example manufactured as described above will be explained with reference to FIG. When a current of 5 A is injected into the amplification regions 101 and 102, the extinction ratio is 20 dB or more, and the 10 dBl attenuation width of the transmitted wavelength is 0.5.
It was a person. Furthermore, as shown in FIG. 2, when no current is applied to the distributed feedback regions 201 and 202, the transmission wavelength is 1.5563 μm. When a current of 80 mA is injected, the transmission wavelength is 1.5505 μm. The transmitted wavelength changed continuously for 58 people.

When there is only one distributed feedback region, the width of the selected wavelength is limited to half of the transmission blocking wavelength region due to the transmission characteristics, resulting in approximately 30 wavelengths, but if there are two distributed feedback regions, each By appropriately adjusting the Bragg wavelength, the range of selected wavelengths can be approximately doubled to 58 wavelengths above the variable wavelength. This situation is shown in FIGS. 4 and 5. Fig. 4 is a diagram showing the relationship between the input waste vector and the output waste vector when there is only one distributed feedback region, and Fig. 5 is a diagram showing the relationship between the input waste vector and the output waste vector when there are two distributed feedback regions. FIG. As shown in FIG. 4, since light having a wavelength in the range A shown in the figure is also transmitted, the wavelength selection width is limited to half of the transmission-blocking wavelength range. However, when there are two distributed feedback regions, the wavelength selection width can be increased as shown in FIG. This actual measurement value is 58 people, which makes it possible to increase the wavelength selection width by about 10 times compared to the wavelength selection width of several people in the conventional optical filter element.

As can be seen from the above, the optical filter element of the present invention makes it possible to select any wavelength from signals wavelength-multiplexed at intervals of about 0.5 people within a range of 58 people. That is,
It can be used as a wavelength tunable filter with over 100 channels.

In the above embodiment, two distributed feedback regions are provided, but this need not be limited to two, and the number of distributed feedback regions may be three or more. Moreover, the number of amplification regions may also be three or more. Furthermore, the material and composition of the element are not limited to the above-described embodiments, and may be other semiconductor materials, dielectric materials, or the like. Further, if the phase shift structure is configured so that the amount of phase shift can be controlled from the outside, the wavelength tuning range can be further expanded. In addition, in the above embodiment, a phase shift diffraction grating is used as the phase shift structure, but it is not necessary to be limited to a phase shift diffraction grating, and it is possible to have a uniform diffraction grating and change the width or thickness of the waveguide. Alternatively, a so-called equivalent phase shift structure may be used. Further, the non-reflective structure may also be a window structure or a multilayer coating.

〔Effect 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 wavelength-multiplexed optical signals of 100 channels or more.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of an optical filter element according to an embodiment of the present invention, FIG. 2 is a diagram showing the transmission characteristics of the optical filter element according to the embodiment of FIG. 1, and FIG. , FIG. 4 is a diagram showing the transmission characteristics of an optical filter element when the amount of phase shift is changed, FIG. 4 is a diagram showing the relationship between the input debris vector and the output debris vector when there is only one distributed feedback region, and FIG. The figure shows the relationship between the input waste vector and the output waste vector when there are two distributed feedback regions. 101.102...Amplification region 110...Substrate 120...Light guide layer 130...Buffer layer 140...Active layers 150, 160...Clad layer 170... ...SiN film 201.202 ...Distributed return area agent Patent attorney Yoshiyuki Iwasa

1 wavelength

Claims (1)

[Claims] (1) A plurality of distributed feedback regions having a phase shift structure and a plurality of active regions are arranged in series and optically coupled, and both end faces of the element have a non-reflection structure. Optical filter element.