JPS61224384A - Wavelength selecting optical switch - Google Patents

Abstract

PURPOSE:To eliminate the necessity of dividing the light including multiple wavelengths in advance and to enable the use of plural means for a control CONSTITUTION:A wavelength selecting switch is composed of a semiconductor P-N junction element 1, an active layer 2 of that, an injection current source 3, an input fiber 4, and an output fiber 5. An impurity concentration of the active layer 2 is restrained to be about 1X10<17>cm<-3> or under. When a signal light including two wavelengths lambda1 and lambda2 from the input fiber 4 is connected to the active layer 2 of the P-N junction element 1, the relative intensity of the P-N junction element 1, the relative intensity of the light of wavelengths lambda1 and lambda2 changes according to the change of the injection current in forward direction to the element 1 and the light is outputted from the output fiber 5. As the impurity concentraion of the active layer 2 is made about 1X10<17>cm<-3>, the absorption of the long wavelength light by free carriers can be prevented. The control of wavelength selection by free carriers enables the high-velocity operation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a compact wavelength-selective light that can switch the wavelength of transmitted signal light at high speed and is used in optical communication and the construction of optical logic circuits. It is related to switches.

Conversion forms between the TB mode and the 7M mode are known. (References, R900Alferness et al.
'Appl.

Phys, Lett,, Vol, MO, PP,
lr & / -r 62. /12) Figure 3 shows an example of the J/FiTi diffused optical waveguide, CocoF.
i ground electrode, 23 is a control electrode, 2 is a mode conversion electrode, 2J- is LiNb0. It is a crystal substrate. To operate this, an analyzer is placed at the output end of waveguide 21, and when a TE monide optical signal enters at a certain wavelength λ, it is converted to 7M mode, emitted, and passes through the analyzer. .

Next, when a voltage is applied to the control electrode 23, LiNb0. Due to the electro-optic effect of , the TE mode is converted to a hull mode at another wavelength λ2. Hence the voltage on.

When turned off, it can be operated as a wavelength selective optical switch. As is clear from the above explanation, in this type of wavelength selection element, the signal light needs to be in either the TFf mode or 7M mode polarization state, which is the polarization state transmitted by a general fiber for optical communication. It does not operate normally in response to disturbed signal light. Also, this element operates by controlling the phase of light.

High manufacturing precision is required. Unstable due to temperature changes,
It has drawbacks such as high insertion loss. In addition, the control width of the center wavelength was 20V and had the disadvantage that it operated only in a very small range of about 2 planes.

The inventor has filed an application for an optical multiplexer/demultiplexer that selectively demultiplexes light of a specific wavelength from light containing multiple wavelengths using a semiconductor PN junction element (Patent Application No. ／♂≠). 6th
The figure shows an example of this, in which a current source 3! is injected in the forward direction of a semiconductor PN junction device 3jC (specifically, a semiconductor laser device). This method takes advantage of the fact that when a bias current is passed through the injected current, an inverted population of carriers is formed, which has an optical amplification function for a specific wavelength range.
In other words, the output of that particular wavelength can be switched. However, with this device, light containing multiple wavelengths must be separated in advance by branch path 3≠, and semiconductor PN junction elements with different specific wavelengths must be prepared for the wavelength of the light to be demultiplexed, and input to each of them. There were drawbacks.

[Problem that the invention seeks to solve]

The present invention uses a single semiconductor PN junction element to configure a wavelength-selective optical switch, so there is no need to pre-divide light containing multiple wavelengths, and multiple control means are used to perform switching. It has the feature that it can use the following means.

[Means and effects for solving the problem] The present invention does not control the phase information of light, but controls the wavelength characteristics of the loss of the semiconductor material when performing switching to select the wavelength. It's something to remember. in particular,
Using a semiconductor PN junction device (specifically, a semiconductor laser device) in which the impurity concentration of the active layer is limited to a certain level or less, when light containing a predetermined wavelength is incident on the active layer of the device and the inflow current is O, the semiconductor Light with a wavelength corresponding to the oscillation wavelength of the laser element is absorbed, and light with a wavelength longer than the oscillation wavelength and corresponding to the band gap energy of the active layer of the element has a small absorption coefficient. Output as transmitted light. At this time, the impurity concentration of the active layer is kept below a certain level (approximately / x / Q"
0flk -3 or less). When a current is injected into the active layer of the device in the forward direction, the number of free carriers increases, and for light with a wavelength corresponding to the oscillation wavelength.

Absorption characteristics are reversed to amplification characteristics. The light on the long wavelength side that was transmitted when the injection current was O becomes absorbed due to the increase in the number of free carriers due to the injection, and is no longer transmitted. By controlling the number of free carriers in the active layer in this way,
Using a single element, it is possible to selectively output light of one of the three wavelengths. In addition to the method using injection current as described above, methods for controlling the number of free carriers in the active layer include a method of injecting control light having a photon energy higher than the band gap energy into the active layer. In this case, direct control of light by light would be realized.Also, by injection of electron beams, application of heat, etc.
It is possible to control the number of free carriers in the active layer, which is the basis of the wavelength selective optical switch and operation of the present invention.

〔Example〕

0 Example/ FIG. 7 shows the first example of the present invention, l is the semiconductor P
N junction element, 2 active layers, 3 is an injection current source, Hiroshi is 7 fibers for input, and Y is an output fiber. The input fiber ≠ and the output fiber pari are processed into a hemispherical shape to create a cylindrical lens effect, and the input fiber ≠
, a signal light including two wavelengths λ1 and λ is coupled to the active layer 2 of the semiconductor PN junction element l. Semiconductor PN junction element
The output from is coupled to output fiber j.

FIG. 2 shows an example of the configuration of an experimental system for confirming the operation of the wavelength selective optical switch of the present invention. t is a light source, 7#'i light receiver, and r is a selection level meter.

As the semiconductor PN junction device, a semiconductor laser device that oscillates at 7.30 μm with an anti-reflection film applied to both end faces is used, and the impurity concentration in the active layer is approximately /X/Q1.
7 (jljk-").The light source 6 has light of 43 μm (λ,), which is the oscillation wavelength of element l, and a longer wavelength of tj μm.
A device that generates light of (λ,) was used. The reason why the impurity concentration of the active layer 2 is limited as described above is to prevent this light of tj' μm from being absorbed by free carriers generated by the impurities.

Ge-APD was used as the IO photodetector.

Using the experimental system shown in Figure 2, light of 43 μm and/or 3 μm is input into a wavelength selective optical switch, the output light is detected by photodetector 7, and a current is injected in the forward direction of the PN junction.

The output characteristics were measured using a selective level meter. FIG. 3 shows the results of measuring the dependence of optical output on injection current. The horizontal axis is the injected current, and the vertical axis is the optical output normalized to the input optical signal level, expressed in decibels. As is clear from this figure, when the injection current is 0, /
, 33 μm wavelength light is output, /, 30 μm optical signal has an attenuation of about 70 dB, but as the injection current increases, this relationship is reversed, and at an injection current of 100 mk, /, 30 μm optical signal The output optical signal of /, 33 μm is about ≠ 0. This results in a dB decrease or attenuation. /, J For an optical signal of 04 m, this corresponds to the oscillation wavelength of a semiconductor laser, so when a forward current is injected into the active layer, free carriers increase and the absorption characteristic reverses to an amplification characteristic for the input signal light. It is. On the other hand, since the signal light of tjj μm has a longer wavelength than the wavelength determined by the band gap energy of the active layer, its absorption coefficient is originally small, and when the current is O, it is transmitted and output although there is some absorption. The increase in absorption as the injection current increases is due to the increase in free carriers. Absorption by free carriers is proportional to the number of free carriers. In this case an increase in absorption of approximately j OdB was observed. As is clear from this figure, the wavelength selective optical switch can be operated by controlling the injection current. Regarding the coupling of signal light to the active layer 2 and the extraction of transmitted light.

It is also effective to use an optical system using general lenses.

0 Example 2 Figure μ shows the second example of the present invention.
N junction element, 10 is an active layer, 11 is an optical waveguide film, /2 is an input lens, 13 is an output lens, 1≠ is a cylindrical lens, 11 is a control light, and /4 is a signal light.

In this example, the active layer 10 of the semiconductor PN junction element is left and etched into a square shape (with a convex cross section).
Slab-type optical waveguide film by applying polyide with a spinner//
was created. Control light /j is incident on this optical waveguide film from the lateral direction via a cylindrical lens l≠, and the optical waveguide film ll
The number of free carriers in the active layer is controlled by irradiating the control light onto the side surface of the active layer io through the active layer io. In this configuration example, a lens/2. /3 was used. It is also possible to use a 7-way IP as in the first embodiment. Light of t μm was input as the signal light, and light of 43 μm was used as the control light. When the control light is not incident, the signal light passes through, but by injecting the control light of about /mW, the signal light can be attenuated by about /OdB, and the effect of the control light that confirmed the switching operation is as follows. This can be achieved by improving the coupling efficiency to the optical waveguide layer 11 by the optical lens lμ and optimizing the thickness of the optical waveguide layer with respect to the thickness of the active layer 10. Furthermore, if the signal light includes light of wavelengths tjjlm and 43 μm, it becomes possible to selectively transmit light of each wavelength as in the first embodiment.

In the above embodiments, the structure using injected current, current, and light as free carrier control means has been described, but it is also possible to use an electron beam, heat, etc. as a control means. The effect of electron beam irradiation is the same as that of light irradiation. In thermal control, since the range in which the temperature of the semiconductor PN junction element can be varied is limited, it is not possible to expect a significant change in the number of free carriers. However, if a configuration for measuring the level or wavelength of the output light is added, it is possible to input a constant signal light and detect heat from changes in the output light. This is also one of the effective ways to utilize the phenomenon that is the basis of the present invention.

〔Effect of the invention〕

As explained above, the wavelength selective optical switch of the present invention has the following advantages because the wavelength selective function is based on the carrier number dependence of the absorption characteristics of the semiconductor material.

(1) Since the structure of the semiconductor PN junction element is similar to that of a laser diode, it can be easily miniaturized and integrated, and can be economically realized through mass production.

(2) To perform wavelength selection control using free carriers/ns
It is possible to operate at relatively high speeds.

(3) Insertion loss is low and gain can be obtained.

(4) Since wavelength selection control can be performed directly using optical signals, it is resistant to electromagnetic induction noise.

(5) Long lifespan as there are no moving parts.

(6) The center wavelength to be switched can be set to a very large value of 2!00 or more.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of the wavelength selective optical switch of the present invention, FIG. 2 is a configuration diagram of an experimental system for confirming the operation of the wavelength selective optical switch of the present invention, and FIG. 3 is a diagram showing a first embodiment of the wavelength selective optical switch of the present invention. Figures illustrating the operation of the wavelength-selective optical switch of the present invention are diagrams illustrating the second embodiment of the wavelength-selective optical switch of the present invention.
The figure shows an example of the configuration of a conventional wavelength selective optical switch, and the second figure shows an example of the configuration of a conventional optical multiplexer/demultiplexer. l, ri, 36... semiconductor PN junction element, 2.10...
・Active layer, 3, 3j... Injection current source, ≠... Input fiber,! ...7 for output, t... light source, 7
...Light reception a, r...Selection level meter, l/...
Optical waveguide film, Ll...Incidence lens, 13...Output lens, l≠...Cylindrical lens, l! ... Control light, 16 ... Signal light, 21 ... Ti diffused optical waveguide, 2
2... Ground electrode, 23... Control electrode, 2≠... Mode conversion electrode, 31/L... Branch path, 37... Output waveguide. Fig. 1 1 ft 2 rgi ¥ 3 fig. 0 5θ / θθ Lightning paste (Hoil A) Kuzu 4 tatami 5th section 2/, z 4 mon modified rhinoceros clay confectionery 6 ta

Claims (1)

[Claims] It consists of a semiconductor PN junction element, a means for inputting signal light into the active layer of the semiconductor PN junction element, a means for extracting the signal light that has passed through the active layer, and a means for controlling the number of free carriers in the active layer. The impurity concentration in the active layer is 1×10^
A wavelength selective optical switch characterized in that the wavelength is 1^7cm^-^3 or less.