JPH01244431A - Variable wavelength filter - Google Patents

Abstract

PURPOSE:To increase variable tuning width and channel number by providing phase control regions which are disposed on both sides of a distribution feedback region, are optically coupled to this region and are capable of controlling the end face phase of said region from the outside. CONSTITUTION:A diffraction grating is formed in the distribution feedback region 100 of an n-InP substrate 110. An InGaAs light guide layer 120, an n-InP buffer layer 130, an active layer 140, and a p-InP clad layer 150 are successively formed thereon. After the layers 150, 140 of the phase control regions 200, 210 are selectively removed, an InP clad layer 160 is formed over the entire part. This filter is made into a flush structure for the purposes of carrier confinement and transverse mode control. Electrodes 300, 310 are formed to the substrate side and the growth layer side and grooves are formed by removing the neighborhood of the mesa at the center. A transmission wavelength moves continuously to a short wavelength side when current I1 is injected to the region 200. The transmission wave moves further to the short wavelength side when current I2 is injected in this state to the region 210.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a variable wavelength filter used for optical transmission, optical exchange, optical information processing, etc.

(Prior art) A tunable wavelength filter has the function of selecting an arbitrary optical signal from wavelength-multiplexed optical signals, and is a key device that can be applied to a wide range of applications such as optical transmission, optical exchange, and optical information processing. -It is. In either application, the characteristics of a variable wavelength filter require sufficient wavelength selectivity and a wide variable tuning width of the selected wavelength. Further, since the structure must be an optical integrated circuit, it is desirable to use a transmission type wavelength selection filter.

Conventionally, several studies have been made on transmission type wavelength selection filters. Among them, a distributed feedback semiconductor laser (DF
There has been a report on the use of a tunable wavelength filter by biasing a BLD below the oscillation threshold. This document includes Applied Physics Letters (App
I can cite the paper written in Volume 51, page 1974 of Lied Physics Letters.

(Problem to be solved by the invention) However, distributed feedback semiconductor lasers (DFB L
A variable wavelength filter in which D) is biased below the oscillation threshold has the following drawbacks.

This variable wavelength filter adjusts the density of carriers injected into the active layer in order to tune the selected wavelength, but the optical gain and spontaneous emission light intensity for the selected wavelength also change at the same time as the selected wavelength. Therefore, in order to obtain the wavelength selectivity necessary for the filter and to obtain the intensity-to-noise ratio, the density of carriers injected into the active layer has been narrowly limited in principle. Therefore, the variable width of the selected wavelength was narrow, and it could only be used as a filter for a few channels.

An object of the present invention is to provide a variable wavelength filter having an amplification function, a variable tuning width of a selected wavelength, and a large number of channels, which overcomes the above-mentioned drawbacks.

(Means for Solving the Problems) The tunable wavelength filter of the present invention includes a distributed feedback region, which is arranged to sandwich the distributed feedback region, is optically coupled to the distributed feedback region, and is externally connected to the distributed feedback region. It is characterized by being composed of a phase control region that can control the end face phase.

(Function) The filter of the present invention is characterized in that wavelength tuning operation and optical gain adjustment can be controlled almost independently. The principle of wavelength tunable operation will now be described. It is known that the transmission wavelength of a guide waveguide having a distributed feedback structure changes greatly depending on the phase at the end faces when both end faces of the distributed feedback structure have reflectance. FIG. 3 shows an example of calculation of mode changes due to the end face phase of the diffraction grating. The horizontal axis is ΔβL (corresponding to wavelength), and the vertical axis is the oscillation threshold gain α. The oscillation threshold gain αL corresponds to the minimum mode or the transmission wavelength of the filter. It can be seen from FIG. 3 that the transmission wavelength changes depending on the end face phase. That is, variable wavelength operation can be realized by controlling the end face phase. In the present invention, phase control regions are provided on both sides of the distributed feedback region in order to control the end face phase. Tunable wavelength operation can be realized with a structure in which the phase control region is provided only on one side of the distributed feedback region, but the wavelength tuning range can be further expanded by providing it on both sides. This phase control region is composed of a light guide that has a forbidden band wider than the energy of the incident light, that is, is transparent to the incident light. When carriers are injected into the phase control region, the transmission refractive index of the optical power decreases due to the plasma effect. Therefore, the phase at both ends of the distributed feedback region changes equivalently, and the equivalent wavelength also changes. On the other hand, optical gain is controlled by carrier injection into the distributed feedback region. In reality, when carriers are injected into the phase control region, the absorption coefficient slightly increases or the oscillation threshold changes, so it is necessary to fine-tune the carriers injected into the distributed feedback region or not. Wavelength and optical gain can be controlled. Therefore, compared to a variable wavelength filter in which a distributed feedback semiconductor laser (DFB LD) whose selected wavelength and optical gain change simultaneously is biased below the oscillation threshold, the wavelength variable tuning width can be increased. Therefore, a filter with a large number of channels can be obtained.

(Example) Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a perspective view showing the structure of a variable wavelength filter according to an embodiment of the present invention. The structure of this embodiment will be explained below based on the manufacturing procedure.

First, a diffraction grating with a period of 2380 is formed in the distributed feedback region +00 of the n-type 1nP substrate 110. Then once [-1
By LPE growth of undoped 1nGaAs photokite layer 120 (), g = 1.3 μm 1 thickness 0
．． 3 μm), n-type lnP buffer layer 130 (thickness
0.1 μm), non-doped active layer 140 (λ, =
+, 53. r1mi thickness 0.1 μm), p-type 1nP
A cladding layer 150 (thickness: 0.2 μm) is sequentially grown. InP cladding layer + of phase control region 200.210
After selectively removing the active layer 140 and the p-type 1nP cladding layer 160, a second LPE growth is performed to form a p-type 1nP cladding layer 160.
form.

A buried structure is used for carrier confinement and transverse mode control. After mesa etching, third LPE growth is performed to perform buried growth.

Here, a double channel planar embedding structure was used as the embedding structure. Finally, after forming electrodes 300 and 310 on the substrate side and the growth layer side, the distributed feedback region +00
In order to electrically isolate the phase control regions 200 and 210, a groove with a width of 20 μm is formed except for the vicinity of the central mesa. The length of the distributed feedback region and the phase control region on one side are each 300/1 m.

100 μm, and the total length of the element is 500 μm.

An example of the characteristics of the device prototyped in this way is shown in Figures 2(a) and (
Shown in b). When a current I of 3 mA is injected into the phase control region 200, the transmission wavelength changes continuously by 4 as shown in Fig. (a).
A: Changed to the short wave side. When a current I2 of 3 mA was injected into the phase control region 210 in this state, the transmission wavelength was further continuously shifted by 4 A to the shorter wavelength side as shown in FIG. During this time, the current injected into the distributed feedback region 100 is adjusted to be 0.98 times the oscillation threshold current. When the incident light intensity is -40 dBm, the gain is 3 of the 27 dB transmission wavelength.
The dB downhand width was 0.4A, and the 10dB downhand width was 0.7X. If -10 dB of crosstalk is allowed, it can be used as a 12-channel filter.

Note that the shrine 1 and composition that constitute the distributed feedback region and phase control region of the element need not be limited to the above-mentioned embodiments, and may be other flat conductor materials (for example, GaAs-based materials) or dielectric materials. Material (e.g. TiO□, Al2O, 3,5in2)
etc. may be used. Further, the guiding waveguide structure may have any structure other than a planar structure or a buried structure as long as it has the function of guiding light.

(Effects of the Invention) Conventional variable wavelength filters were limited to a few channels, but the variable wavelength filter of the present invention makes it possible to select any wavelength from a wavelength multiplexed optical signal of IO channels or more.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention. Second
Figures (a) and (b) are diagrams showing the transmission characteristics of the variable wavelength filter of this example. FIG. 3 is a diagram showing an example of 3A calculation of mode changes due to the end face phase of a diffraction grating. In the figure, 100 - distributed feedback region, 110 - substrate, 120 - optical guide layer, 130 - buffer layer 140 - active layer, 15θ
, 160~cladding layer 200.210~layer control region 3
00.310~electrode.

Claims (1)

[Claims] It is characterized by being composed of a distributed feedback region and a phase control region arranged to sandwich the distributed feedback region, optically coupled to the distributed feedback region, and capable of controlling the end face phase of the distributed feedback region from the outside. tunable wavelength filter.