Re: [10GMMF] task 4 Oct. 4th call -- Polarization
Thank you, Stefano. This is helpful. If I have any questions later, I will
get back to you.
Vipul
> -----Original Message-----
> From: owner-stds-802-3-10gmmf@IEEE.ORG
> [mailto:owner-stds-802-3-10gmmf@IEEE.ORG]On Behalf Of
> Bottacchi.external@INFINEON.COM
> Sent: Monday, October 11, 2004 6:07 AM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] task 4 Oct. 4th call -- Polarization
> Importance: High
>
>
> Vipul,
>
> thank you for your pertinent comments. Let me try to explain why
> polarization works in multimode fiber when offset is taken into account.
> I completely agree with you on the fundamental mode solution for the
> axial symmetric fiber.
>
> Let us continue to assume the fiber has rotational symmetry and the
> vector wave equation reduces to the well known Helmoltz scalar equation.
> According to weakly guiding approximation WGA, all modes belonging to
> the same mode group exhibit the same propagation constant and therefore
> have the same group velocity (this is strictly true within the WGA, but
> it is not relevant for the discussion).
>
> One important statement is that the whole mode solution (geometrical
> mode structure) refers to the assumed polarization of the electric
> field. It is customary to assume the x-axis oriented along the linear
> polarization of the electric field. At this point, if mode excitation
> would be still axial symmetric (OFL), any polarization effect would be
> observed. "Everything" would be the same independently from any
> azimuthal position.
>
> What is important now is the result of the overlapping integral at the
> launching section to calculate the amount of intensity transferred to
> each mode group. If the excitation is eccentric, defined through some
> offset coordinate, the coupling coefficients will depend on the relative
> orientation of the linear polarization (reference x-axis) and the
> (r,phi) coordinate of the offset center.
>
> This is the important point. For a given mode group assembled by several
> modes with the same propagation constant, the amount of intensity
> transferred between two offset fibers depends on the relative
> orientation of the offset respect to the light polarization. In
> addition, at the same radial coordinate region belong different mode
> groups with different group velocity.
>
> Assuming the profile is not optimized we experience a polarization
> induced DMD which leads to pulse distortion after few hundreds of meters
> at the 10GbE scale.
>
> I hope to have been clearer in this picture description. This is not in
> contradiction with well known mode theory. It just consider one
> different situation where polarization, offset and profile optimization
> play the role in getting pulse distortion.
>
> Please, I apologize if something was missing or uncorrected. Looking
> forward in receiving your comments,
>
> Best regards
>
> Stefano
>
> -----Original Message-----
> From: owner-stds-802-3-10gmmf@IEEE.ORG
> [mailto:owner-stds-802-3-10gmmf@IEEE.ORG] On Behalf Of Vipul Bhatt
> Sent: Donnerstag, 7. Oktober 2004 20:34
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: Re: [10GMMF] task 4 Oct. 4th call -- Polarization
>
>
> I appreciate the work done by Joerg and his team, and the polarization
> experiment report seems well organized, but...polarization penalty for
> multimode links? I hope someone can educate me, because the way I see
> it, polarization shouldn't make any difference to DMD.
>
> I am starting with the assumption that only the input polarization was
> changed, and everything else was unchanged -- i.e., the excitation
> region didn't shift, the input field intensity pattern remained the
> same, etc.
>
> DMD changes only if the power distribution among mode groups changes. A
> mode group consists of one or more LP modes having nearly identical
> propagation constant. My contention is that a change in input
> polarization not only leaves power in each mode group intact, but it
> also leaves power in each mode intact.
>
> We normally characterize a mode as LP(m,n), where m is the azimuthal
> number and n is the radial number. But actually, each LP(m,n) mode
> consists of two (if m=0) or four (if m>0) distinguishable modes having
> the same propagation constant -- distinguishable because of two possible
> polarizations and two possible azimuthal orientations, sine and cosine.
> For example, mode group 6 consists of LP(5,1), LP(3,2) and LP(1,3), and
> has a total of 12 distinguishable modes.
>
> Power in each LP mode is the sum of the powers carried by its
> distinguishable modes. These distinguishable modes share the power, the
> proportion being decided by how the input polarization aligns with the
> polarization axes of the distinguishable modes. When the input
> polarization direction is changed, the proportion of power among these
> distinguishable modes changes, but the total power in an LP mode remains
> the same. Therefore, DMD should not be affected by changes in input
> polarization.
>
> Please tell me what I am missing. Thank you.
>
> Vipul
>
> Vipul_Bhatt@ieee.org
> +1-650-941-6290
>
> -----Original Message-----
> From: owner-stds-802-3-10gmmf@IEEE.ORG
> [mailto:owner-stds-802-3-10gmmf@IEEE.ORG]On Behalf Of yusun@IEEE.ORG
> Sent: Wednesday, October 06, 2004 9:04 AM
> To: STDS-802-3-10GMMF@listserv.ieee.org
> Subject: [10GMMF] the minitues of task 4 Oct. 4th call
>
>
> Dear colleagues,
>
> I attached the minutes of tele-conference of task 4 group on Oct. 4th. I
> would appreciate your comments. The proposed next task 4 meeting is Oct
> 11th, 2004 (Monday), 11am east coast, 8 am west coast and 4 pm UK.
>
> Best regards,
>
> Yu