JPH03282433A - Wavelength conversion device - Google Patents

Abstract

PURPOSE:To simplify an optical isolator and an optical system by imposing optical intensity modulation upon a frequency-modulated signal which has specific wavelength in a multiplexed converted light group, and making this intensity-modulated light incident on a laser which oscillates with the wavelength of a transmission destination not in the direction of the optical axis of the laser resonator. CONSTITUTION:A wavelength filter 4 whose light output is adjustable with multiplexed different-wavelength wavelenth-converted light beams 1 which have frequency modulated signals converts the frequency-modulated signal light 2. Then the signal is made incident on the flank of the semiconductor laser 5 which oscillates with the target wavelength. The laser intensity is varied with the incident light 2 which varies in incidence intensity and wavelength variation is caused at the same time to cause frequency variation. The optical axis 3-3' of the oscillation laser and the optical axis 2-2' of the incident light are different from each other, so oscillation light beams 3 and 3' are not coupled with the frequency filter 4 by the flank incidence method and the optical isolator is therefore needed. Consequently, the optical system is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of transmitting frequency modulated signals during exchange using wavelength conversion in optical communications.

[Conventional technology]

One method of increasing the transmission capacity of optical communications is wavelength division multiplexing, in which multiple wavelengths are transmitted through a single optical fiber.

If it becomes possible to exchange signals between these multiplexed signal lights, that is, to perform "wavelength exchange," the functionality of optical communication will further improve.The key to wavelength exchange is as follows.
It is a means for transmitting information (signal) in the converted light to the converted light.

Direct transmission of optical signals without converting them into electrical signals is strongly desired from the viewpoint of ease of construction, speed, etc.

As a method of transmitting this signal, a method using four-wave mixing that takes advantage of nonlinearity within an optical amplifier is described in IOC '89 Technical Digest Volume 2 (
1989) pp. 136-137 (I OOC'
8 9 Technical DigestVo
12.2 pp, 136-137 (1989))
It is stated in The principle of this method is that excitation light called pump light, which has a wavelength close to the wavelength of signal light, is superimposed and input into an optical amplifier, and then light called probe light, which has a wavelength to which the signal is to be transferred, is input. Light that reflects the signal light appears at a location where the wavelength of the difference in light is shifted from the probe light, and the information in the signal light is transmitted to light of a different wavelength.

However, in the above method, the wavelength ranges of the converted light and the converted light must be different, so it cannot be directly applied when the multiplexed wavelength ranges are the same, and the modulated light output is on the order of μW. There were problems such as low

On the other hand, a method is described in Electronics Letters, Vol. 1989) No. 136
Shown on pages 0 to 1362.

In this method, the light that has been converted to 1-intensity modulation is made incident perpendicularly to the polarization of the laser that emits the converted light so as not to cause interference with the converted light, and it is confirmed that the converted light is actually frequency modulated. ing.

[Problem to be solved by the invention]

The above-mentioned conventional technology has a configuration in which intensity-modulated light that is perpendicular to the polarization of the laser is incident from on the optical axis of a semiconductor laser that emits modulated light. Since the structure is such that the intensity is adjusted using an optical amplifier before inputting the light, it was necessary to insert an optical isolator with high isolation to prevent the light from the modulated light from coupling to the optical amplifier and disturbing the amplification characteristics. The situation is the same even if this configuration is partially changed and an active filter is used instead of the optical amplifier and filter. Since it is necessary to incorporate this optical isolator, a one-chip configuration is not possible. Furthermore, in order to obtain information from optical signals that are on the same optical axis, it was necessary to insert an optical branch to intercept some of the light and receive it at the optical receiver.

The purpose of the present invention is to separate the optical axis of the signal light that has converted the converted light into intensity modulated light and the optical axis of the laser that emits the converted light,
The objective is to simplify optical isolators and optical systems related thereto.

Another object of the present invention is to extract signals without using optical branches.

A further object of the present invention is to enable transmission of a frequency modulated signal between input light and output light using a single chip.

Still another object of the present invention is to provide a structure that can sufficiently modulate the frequency of a semiconductor laser even with a weakened input signal after transmission.

[Means to solve the problem]

In order to achieve the above object, the device of the present invention takes means for converting a frequency modulated signal of a specific wavelength into light intensity modulation from among a multiplexed group of converted light, and then transmits this intensity modulated light. As a method of inputting light into a laser that oscillates at the destination wavelength, the laser resonator has a structure in which the light is input from a direction other than the optical axis of the laser resonator.

In addition, in order to achieve the other objects mentioned above, a light receiver is arranged so as to receive the intensity-modulated light transmitted by the laser.

In order to achieve yet another purpose, on one substrate, (1) select the light to be converted, (2) change the frequency modulation to intensity modulation, and (3) irradiate the laser that emits the converted light. It forms a structure with two functions.

In order to achieve the fourth objective above, the optical waveguide constituting the wavelength filter and the optical waveguide of the semiconductor laser are diagonally crossed, or the wavelength filter is made into a λ/4 phase shift distributed feedback laser structure, and the center This crosses the semiconductor laser.

[Effect]

The basic configuration and operating principle will be explained using FIG.

The basic configuration includes a frequency filter 4 and a laser 5.
The arrangement is such that the light 2 emitted from the frequency filter 4 is transmitted to the laser 5.
The purpose of the present invention is to arrange the light so that it enters from a side direction that does not coincide with the optical axis direction 3-3' of the separated light.

The principle of operation is that a wavelength filter 4 whose optical power can be adjusted from a multiplexed wavelength-converted light 1 of a plurality of different wavelengths having a frequency modulation signal, for example, a combination of a Matsu A-Zender interference system and an optical amplifier, or a semiconductor laser. A frequency modulated signal of a specific wavelength is converted into intensity modulated signal light 2 by an active filter that operates below the oscillation threshold.

Next, the semiconductor laser 5 oscillating at the wavelength to which you want to transfer the signal
incident from the side. For example, the applied physics letter 51. (
1987) pp. 1780-1782 (Appl.
Phys, Lett, 51 (22) p p.

1780-1782 (1987)), the laser light intensity changes. Since this output fluctuation is accompanied by carrier fluctuation, a wavelength change occurs at the same time, resulting in a frequency change. Conventionally, the purpose was to stop laser oscillation. For this reason, there was no description at all for use in frequency modulation. In this way,
Conveys frequency modulated signals.

In the side injection method, since the optical axis 33' of the oscillating laser and the optical axis 2-2' of the incident light are different, the oscillating lights 3 and 3' are never coupled to the frequency filter 4. Therefore, an optical isolator is not required. Further, by receiving the transmitted light 2' of the intensity modulated light 2 with the light receiver 6, it is possible to simultaneously collect information to be transmitted.

Furthermore, in this configuration, by configuring the frequency filter with a semiconductor laser and having a configuration in which the semiconductor laser 5 for converted light and the waveguide intersect, it becomes possible to integrate the frequency filter into one chip.

Furthermore, in order to effectively couple the light from the wavelength filter and the semiconductor laser for weak input light, when the optical waveguides for both are diagonally crossed, the crossing angle is set to θ.

If the width df of the wavelength filter and the width d of the semiconductor laser are set, the intersection area S becomes S '' d i・d,/cosθ, and the intersection area can be expanded.Also, as a wavelength filter, a λ/4 phase shift distribution feedback type is used. By adopting the laser structure, the light intensity becomes concentrated in the λ/4 phase shift region.By arranging the optical waveguide of the semiconductor laser in this λ/4 phase shift region, the light inside the wavelength filter and the semiconductor Lasers can be effectively coupled.

〔Example〕

Example 1 An example will be described with reference to FIG. In the figure (a), a signal light l from an optical fiber 11 through which a plurality of modulated light beams propagate is coupled to a wavelength conversion element that includes a wavelength filter 40, a semiconductor laser 50, and a light receiver 60 formed on one chip, and the converted light is 3
FIG. 2 is a top view of a configuration for outputting. FIG. 2B is a sectional view taken along line AA' of the semiconductor laser section at 5 degrees. (c) is a BB' cross-sectional view of the wavelength filter 40 and the light receiver 60 part.

The configuration seen from the top will be explained using FIG.

The wavelength conversion element is a semiconductor laser 5 consisting of one electrode 51.
The electrode 51 of the semiconductor laser is arranged so as to be approximately perpendicular to 0.
An active wavelength filter 40 consisting of two electrodes 41 and 42 separated from each other and arranged on an extension line of the wavelength filter,
It is composed of a light receiver 60 having an independent electrode 61.

Next, the cross-sectional structure and its manufacturing method will be described using (b) and (c).

First, on an n-type InP substrate, in the area of the semiconductor laser 50, a diffraction grating 17 having uneven undulations in the stripe direction A-A' of the semiconductor laser 50, and in the area of the wavelength tunable filter 40, unevenness perpendicular to the direction of the unevenness are formed. Form. This can be patterned by using an electron beam drawing device or by phase projection method, performing two-beam interference exposure without partially masking, and changing the exposure direction in each region.

After that, for example, InGaAsP with a bandgap wavelength λg of 1.3 μm is grown by liquid phase wavelength method or vapor phase crystal growth method.
A quaternary mixed crystal is used as the guide layer 13, and the λ-thickness is 1.55 μm.
InGaAsP quaternary mixed crystal active layer height is 15, anti-melt butt layer 15 is p-type InP cladding layer 16.1g is p
Crystal growth is performed using a 1.15 μm type InGaAsP quaternary mixed crystal as a cap N17. After that, the semiconductor laser 5
0. Wavelength filter 40. A width of 1 to several μ in the area of the photoreceiver 60
The region of the crystal growth layer other than the stripes is removed by etching so that m stripes remain.

In particular, in the region of the semiconductor laser 50, the active layer 14 is made to have a width of about 1 μm so that it oscillates at a single wavelength. On the other hand, the wavelength filter 40 has a width of several μm and may have a plurality of natural oscillation wavelengths, but there is no problem if it is set so that one oscillation wavelength can be obtained within the selected wavelength range.

For example, the thickness of the guide layer 13 is ~0.25 μm, the thickness of the active layer 14 is ~0.13 μm, and the anti-meltback layer 1 is
When the thickness of the semiconductor laser 5o is ~0.04 μm, and the pitch of the diffraction grating 19 of the semiconductor laser 5o is 0.238 μm, the oscillation wavelength is approximately 1.540 μm when the width of the active layer is 1 μm.
It becomes μm. On the other hand, the width of the active layer of a wavelength filter cannot be made as narrow as 1 μm due to the influence of the crystal orientation on the etching shape, and may be as wide as 4 μm, but the pitch of the diffraction grating can be set to 0.233 μm. The wavelength range of the optical filter 40 can be made to match 1.540 μm. After forming the stripes, a current blocking layer is crystal-grown in areas other than the stripes. Finally, P electrodes 51, 41, 42° 61 are formed in each region, and an N electrode 71 is formed. The wavelength filter and semiconductor laser are DFB (
It is a distributed feedback (distributed feedback) laser structure.

A current was applied to this device to cause the semiconductor laser 50 to oscillate at the oscillation threshold current No. 2, and the wavelength of the main mode at the oscillation threshold was measured by changing the current ratio of the electrodes 41 and 42 of the wavelength filter, and it was 1.54 μm ± o, oosμm changed. In order to use this as a wavelength filter, the oscillation threshold is set to about 0.98 below the oscillation threshold.
The injection currents of electrodes 41 and 42 were set. In this state, 2 GHz with a wavelength of 1.542 μm is transmitted from the optical fiber 11.
A signal light with frequency modulation was input. Light receiver 60
Add reverse bias to and monitor this signal.

By changing the ratio of the currents injected into the wavelength filter 40, it was possible to extract an electrical output corresponding to the signal of the input light 1 from the light receiver at a specific ratio.

By adjusting the current ratio of the wavelength filter so that the output of the photoreceiver becomes a specific value, the output light 3 of the semiconductor laser 50 having a wavelength of 1.540 μm is received as a frequency modulation of 2 GHz. Other input light within a wavelength of 1.540±0.005 μm was also investigated, and a frequency modulated signal was similarly transmitted to the semiconductor laser output light 3 having a wavelength of 1.540 μm.

Example 2 Another example will be described using FIG. 3. The difference from Example 1 is that the semiconductor laser 50 has three electrodes, namely:
This point is separated into 52, 53, and 54 points. By separating the electrodes in this way, the oscillation wave of the semiconductor laser 50 can be changed within the range of 1.540 μm±o, o s μm. The same measurements as in Example 1 were performed, and it was confirmed that a frequency modulated signal was transmitted at any wavelength.

Example 3 Another example will be described using FIG. 4. The difference from Examples 1 and 2 is that the semiconductor laser 50 is a three-electrode wavelength tunable DBR (Distributed Bragg Reflection) laser. This three-electrode wavelength tunable DBR laser 50 has three
It has nine regions, a Bragg reflection region (a region to which electrode 55 corresponds), nine phase adjustment regions (a region to which electrode 56 corresponds), and a light amplification region (a region to which electrode 57 corresponds). The first two are formed by passive optical waveguides, for example, λg=x, 3 μm,
The oscillation wavelength is changed using the change in refractive index caused by injected carriers. The wavelength filters 40 are arranged so as to intersect at a part of the optical amplification region of the wavelength tunable laser 50. Since this wavelength tunable DBP laser can change the wavelength range up to about 3 nm, the range of wavelength settings is wider than in the second embodiment. As a result of measurement in the same manner as in the previous example, transmission of the same numerically modulated signal was confirmed.

Example 4 This will be explained using FIG. 5. In this embodiment, the wavelength filter 4
If the intersection angle between 0 and the semiconductor laser 50 is 60 degrees, the intersection area will be doubled. In actual measurements, there was a bending loss in the optical fiber 11 and the wavelength filter 40, and although the loss was not doubled, an improvement was observed.

Example 5 This will be explained using FIG. 2. Although the structure is almost the same as that of Example 1, there are two points.

One is the structure of the diffraction grating 8 of the wavelength filter 40.

The phase of the left and right unevenness of the diffraction grating 18 is reversed with respect to the area intersecting the semiconductor laser 50 in the center.
It has a four-phase shift structure. Furthermore, a non-reflection coating of SiN is applied to eliminate the influence of reflection from the end face on the incident side. By adopting this structure, it was possible to stably obtain sufficient modulation of the semiconductor laser light 3 even at a low input level. An average level difference of 2 dB was observed between when this specific structure was used and when it was not.

〔Effect of the invention〕

According to the present invention, signal transmission when performing wavelength conversion is
At the same time as it can be done directly with light, (1) the optical system is simple, (2) the frequency modulation signal can be controlled directly by the intensity of the electrical signal at the receiver from changes in light intensity, and (3) it can be made into one chip. This makes it possible to simplify the configuration and improve reliability in optical communications.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the basic configuration of the present invention, and FIG. 3 and 4 show a device according to an embodiment of the present invention, respectively (a) is a top view, (b) and (C) are sectional views, and FIG. 5 is a device according to another embodiment of the present invention. FIG. 1... Hexagonal light to be converted with frequency modulation signal, 2゜2
′... Kugata light converted to intensity modulation signal, 3゜3′・
... Semiconductor laser output light, 4... Wavelength filter. 5... Semiconductor laser that emits light at the wavelength of the conversion destination, 6.
...Receiver, 11...Optical fiber, 12...n type I
nP substrate, 13-InGaAsP guide layer, 14 ・
・・InGaAsP active layer, 15”・InGaAsP
anti-meltback layer, 16... p-type InP cladding layer, 17... InGaAsP cap layer, 18.
... Diffraction grating for active wavelength filter, 19... Diffraction grating for semiconductor laser, 40... Wavelength filter, 41.42
... Electrode for wavelength tunable wavelength filter, 51... Electrode for semiconductor laser, 52-57... Electrode for wavelength tunable semiconductor laser, 60... Light receiver, 61... Electrode for light receiver, 7
1...n electrode, 72... wavelength filter entrance end face.

Claims (1)

[Claims] 1. There is intensity modulated light having at least one first wavelength, and this intensity modulated signal is transmitted to a semiconductor laser that oscillates at a second wavelength within the semiconductor laser gain or absorption wavelength range. 1. A wavelength conversion device having a configuration for transmitting an optical signal of a first wavelength in the form of frequency modulation of a second wavelength by irradiating from a side surface of a resonator of a semiconductor laser when there is a first wavelength. 2. The wavelength conversion device according to claim 1, wherein the intensity-modulated light having the first wavelength is light obtained by converting frequency-modulated light having the first wavelength into intensity-modulated light using a wavelength filter. . 3. The device of claim 1, wherein the irradiated first
A wavelength conversion device characterized by extracting a portion of light with a wavelength of , as an electrical signal using a light receiver. 4. The optical waveguide for the wavelength filter that selects the frequency modulated light of the first wavelength and converts it into intensity modulation is arranged so that the optical axes of the optical waveguide of the semiconductor laser that emits light at the second wavelength intersect. Featured wavelength conversion device. 5. The wavelength conversion device according to claim 4, wherein each element is formed monolithically. 6. The wavelength conversion device according to claim 5, wherein the light receiver is monolithically formed on an extension of the optical axis of the optical waveguide of the wavelength filter. 7. The wavelength conversion device according to claim 4, wherein the two optical waveguides intersect at an angle. 8. The wavelength conversion device according to claim 4, wherein the wavelength filter is composed of a λ/4 phase shift diffraction grating, and the phase shift region has a crossing region.